Network Security
(Course Details)
By
ASIM SHAHZAD
Assistant Professor
University Of Engineering And Technology Taxila
Name Asim Shahzad MS Telecom Engineering (ICT) MS Computer Engineering (UET Taxila) Currently started PhD in area of Solitons
propagation in Fiber Optics Communication from UET Taxila
Emailasimshahzaduettaxilaedupk
Contact no 0300 9755694
Theme of Course
1 Module 1 (Cryptography) Introduction to Security terms and Algorithms Overview of Symmetric and Asymmetric Cryptographic Algorithms
2 Module 2 (Security Architectures and Models) Security in Network Multilayer Security
3 Module 3 (Operations Security) TCSEC (Trusted Computer Security Evaluation Criteria) The Orange Book Vulnerabilities of Networked Applications Worms viruses malicious codes arriving from networks attack on infrastructure
4 Module 4 (Defense Technologies) Protection of information in transit Application and Transport Layer security
Protocols Protection of Networked Applications Firewalls and IPS
5 Module 5 (Application and System Development) Kerberos IPSec SSLTLS (Case Studies)
6 Module 6 (Security Management) Security Planning Physical Security Disaster Recovery Law Investigation Ethics Ethical Hacking
Marks Breakdown
Total Marks 150
External marks 25 Final 100 Internal Sessional Work 25
Passing Marks 75
Two parts of your course How to secure data (data security) How to secure your networks (network security) we start from data security talk
about its various aspects major concern will be ciphers designing
Desirable Security Properties
Authenticity Confidentiality Integrity Availability Accountability and non-repudiation Freshness Access control Privacy of collected information
Cryptology
1048708 Some Terminologies 1048708 Plain text The original message 1048708 Cipher Text The coded message 1048708 Cipher algorithm for transforming plaintext
to cipher text 1048708 Key info used in cipher known only to
senderreceiver 1048708 Encipher (encrypt) converting plaintext to
cipher text 1048708 Decipher (decrypt) recovering cipher text
from plaintext
Contdhellip
Cryptography study of encryption principlesmethods
Cryptanalysis (code breaking) the study of principles methods of deciphering cipher text without knowing key
Cryptology the field of both cryptography and cryptanalysis
Contd
1048708 Unconditional security No matter how much computer power is
available the cipher cannot be broken since the cipher text provides insufficient information to uniquely determine the corresponding plaintext
Computational security Given limited computing resources (eg time
needed for calculations is greater than age of universe) the cipher cannot be broken
Conventional Encryption Principles
1048708 An encryption scheme has five ingredients
1048708 Plaintext 1048708 Encryption algorithm 1048708 Secret Key 1048708 Cipher text 1048708 Decryption algorithm 1048708 Security depends on the secrecy of the
key not the secrecy of the algorithm
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Name Asim Shahzad MS Telecom Engineering (ICT) MS Computer Engineering (UET Taxila) Currently started PhD in area of Solitons
propagation in Fiber Optics Communication from UET Taxila
Emailasimshahzaduettaxilaedupk
Contact no 0300 9755694
Theme of Course
1 Module 1 (Cryptography) Introduction to Security terms and Algorithms Overview of Symmetric and Asymmetric Cryptographic Algorithms
2 Module 2 (Security Architectures and Models) Security in Network Multilayer Security
3 Module 3 (Operations Security) TCSEC (Trusted Computer Security Evaluation Criteria) The Orange Book Vulnerabilities of Networked Applications Worms viruses malicious codes arriving from networks attack on infrastructure
4 Module 4 (Defense Technologies) Protection of information in transit Application and Transport Layer security
Protocols Protection of Networked Applications Firewalls and IPS
5 Module 5 (Application and System Development) Kerberos IPSec SSLTLS (Case Studies)
6 Module 6 (Security Management) Security Planning Physical Security Disaster Recovery Law Investigation Ethics Ethical Hacking
Marks Breakdown
Total Marks 150
External marks 25 Final 100 Internal Sessional Work 25
Passing Marks 75
Two parts of your course How to secure data (data security) How to secure your networks (network security) we start from data security talk
about its various aspects major concern will be ciphers designing
Desirable Security Properties
Authenticity Confidentiality Integrity Availability Accountability and non-repudiation Freshness Access control Privacy of collected information
Cryptology
1048708 Some Terminologies 1048708 Plain text The original message 1048708 Cipher Text The coded message 1048708 Cipher algorithm for transforming plaintext
to cipher text 1048708 Key info used in cipher known only to
senderreceiver 1048708 Encipher (encrypt) converting plaintext to
cipher text 1048708 Decipher (decrypt) recovering cipher text
from plaintext
Contdhellip
Cryptography study of encryption principlesmethods
Cryptanalysis (code breaking) the study of principles methods of deciphering cipher text without knowing key
Cryptology the field of both cryptography and cryptanalysis
Contd
1048708 Unconditional security No matter how much computer power is
available the cipher cannot be broken since the cipher text provides insufficient information to uniquely determine the corresponding plaintext
Computational security Given limited computing resources (eg time
needed for calculations is greater than age of universe) the cipher cannot be broken
Conventional Encryption Principles
1048708 An encryption scheme has five ingredients
1048708 Plaintext 1048708 Encryption algorithm 1048708 Secret Key 1048708 Cipher text 1048708 Decryption algorithm 1048708 Security depends on the secrecy of the
key not the secrecy of the algorithm
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Theme of Course
1 Module 1 (Cryptography) Introduction to Security terms and Algorithms Overview of Symmetric and Asymmetric Cryptographic Algorithms
2 Module 2 (Security Architectures and Models) Security in Network Multilayer Security
3 Module 3 (Operations Security) TCSEC (Trusted Computer Security Evaluation Criteria) The Orange Book Vulnerabilities of Networked Applications Worms viruses malicious codes arriving from networks attack on infrastructure
4 Module 4 (Defense Technologies) Protection of information in transit Application and Transport Layer security
Protocols Protection of Networked Applications Firewalls and IPS
5 Module 5 (Application and System Development) Kerberos IPSec SSLTLS (Case Studies)
6 Module 6 (Security Management) Security Planning Physical Security Disaster Recovery Law Investigation Ethics Ethical Hacking
Marks Breakdown
Total Marks 150
External marks 25 Final 100 Internal Sessional Work 25
Passing Marks 75
Two parts of your course How to secure data (data security) How to secure your networks (network security) we start from data security talk
about its various aspects major concern will be ciphers designing
Desirable Security Properties
Authenticity Confidentiality Integrity Availability Accountability and non-repudiation Freshness Access control Privacy of collected information
Cryptology
1048708 Some Terminologies 1048708 Plain text The original message 1048708 Cipher Text The coded message 1048708 Cipher algorithm for transforming plaintext
to cipher text 1048708 Key info used in cipher known only to
senderreceiver 1048708 Encipher (encrypt) converting plaintext to
cipher text 1048708 Decipher (decrypt) recovering cipher text
from plaintext
Contdhellip
Cryptography study of encryption principlesmethods
Cryptanalysis (code breaking) the study of principles methods of deciphering cipher text without knowing key
Cryptology the field of both cryptography and cryptanalysis
Contd
1048708 Unconditional security No matter how much computer power is
available the cipher cannot be broken since the cipher text provides insufficient information to uniquely determine the corresponding plaintext
Computational security Given limited computing resources (eg time
needed for calculations is greater than age of universe) the cipher cannot be broken
Conventional Encryption Principles
1048708 An encryption scheme has five ingredients
1048708 Plaintext 1048708 Encryption algorithm 1048708 Secret Key 1048708 Cipher text 1048708 Decryption algorithm 1048708 Security depends on the secrecy of the
key not the secrecy of the algorithm
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Marks Breakdown
Total Marks 150
External marks 25 Final 100 Internal Sessional Work 25
Passing Marks 75
Two parts of your course How to secure data (data security) How to secure your networks (network security) we start from data security talk
about its various aspects major concern will be ciphers designing
Desirable Security Properties
Authenticity Confidentiality Integrity Availability Accountability and non-repudiation Freshness Access control Privacy of collected information
Cryptology
1048708 Some Terminologies 1048708 Plain text The original message 1048708 Cipher Text The coded message 1048708 Cipher algorithm for transforming plaintext
to cipher text 1048708 Key info used in cipher known only to
senderreceiver 1048708 Encipher (encrypt) converting plaintext to
cipher text 1048708 Decipher (decrypt) recovering cipher text
from plaintext
Contdhellip
Cryptography study of encryption principlesmethods
Cryptanalysis (code breaking) the study of principles methods of deciphering cipher text without knowing key
Cryptology the field of both cryptography and cryptanalysis
Contd
1048708 Unconditional security No matter how much computer power is
available the cipher cannot be broken since the cipher text provides insufficient information to uniquely determine the corresponding plaintext
Computational security Given limited computing resources (eg time
needed for calculations is greater than age of universe) the cipher cannot be broken
Conventional Encryption Principles
1048708 An encryption scheme has five ingredients
1048708 Plaintext 1048708 Encryption algorithm 1048708 Secret Key 1048708 Cipher text 1048708 Decryption algorithm 1048708 Security depends on the secrecy of the
key not the secrecy of the algorithm
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Two parts of your course How to secure data (data security) How to secure your networks (network security) we start from data security talk
about its various aspects major concern will be ciphers designing
Desirable Security Properties
Authenticity Confidentiality Integrity Availability Accountability and non-repudiation Freshness Access control Privacy of collected information
Cryptology
1048708 Some Terminologies 1048708 Plain text The original message 1048708 Cipher Text The coded message 1048708 Cipher algorithm for transforming plaintext
to cipher text 1048708 Key info used in cipher known only to
senderreceiver 1048708 Encipher (encrypt) converting plaintext to
cipher text 1048708 Decipher (decrypt) recovering cipher text
from plaintext
Contdhellip
Cryptography study of encryption principlesmethods
Cryptanalysis (code breaking) the study of principles methods of deciphering cipher text without knowing key
Cryptology the field of both cryptography and cryptanalysis
Contd
1048708 Unconditional security No matter how much computer power is
available the cipher cannot be broken since the cipher text provides insufficient information to uniquely determine the corresponding plaintext
Computational security Given limited computing resources (eg time
needed for calculations is greater than age of universe) the cipher cannot be broken
Conventional Encryption Principles
1048708 An encryption scheme has five ingredients
1048708 Plaintext 1048708 Encryption algorithm 1048708 Secret Key 1048708 Cipher text 1048708 Decryption algorithm 1048708 Security depends on the secrecy of the
key not the secrecy of the algorithm
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Desirable Security Properties
Authenticity Confidentiality Integrity Availability Accountability and non-repudiation Freshness Access control Privacy of collected information
Cryptology
1048708 Some Terminologies 1048708 Plain text The original message 1048708 Cipher Text The coded message 1048708 Cipher algorithm for transforming plaintext
to cipher text 1048708 Key info used in cipher known only to
senderreceiver 1048708 Encipher (encrypt) converting plaintext to
cipher text 1048708 Decipher (decrypt) recovering cipher text
from plaintext
Contdhellip
Cryptography study of encryption principlesmethods
Cryptanalysis (code breaking) the study of principles methods of deciphering cipher text without knowing key
Cryptology the field of both cryptography and cryptanalysis
Contd
1048708 Unconditional security No matter how much computer power is
available the cipher cannot be broken since the cipher text provides insufficient information to uniquely determine the corresponding plaintext
Computational security Given limited computing resources (eg time
needed for calculations is greater than age of universe) the cipher cannot be broken
Conventional Encryption Principles
1048708 An encryption scheme has five ingredients
1048708 Plaintext 1048708 Encryption algorithm 1048708 Secret Key 1048708 Cipher text 1048708 Decryption algorithm 1048708 Security depends on the secrecy of the
key not the secrecy of the algorithm
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Cryptology
1048708 Some Terminologies 1048708 Plain text The original message 1048708 Cipher Text The coded message 1048708 Cipher algorithm for transforming plaintext
to cipher text 1048708 Key info used in cipher known only to
senderreceiver 1048708 Encipher (encrypt) converting plaintext to
cipher text 1048708 Decipher (decrypt) recovering cipher text
from plaintext
Contdhellip
Cryptography study of encryption principlesmethods
Cryptanalysis (code breaking) the study of principles methods of deciphering cipher text without knowing key
Cryptology the field of both cryptography and cryptanalysis
Contd
1048708 Unconditional security No matter how much computer power is
available the cipher cannot be broken since the cipher text provides insufficient information to uniquely determine the corresponding plaintext
Computational security Given limited computing resources (eg time
needed for calculations is greater than age of universe) the cipher cannot be broken
Conventional Encryption Principles
1048708 An encryption scheme has five ingredients
1048708 Plaintext 1048708 Encryption algorithm 1048708 Secret Key 1048708 Cipher text 1048708 Decryption algorithm 1048708 Security depends on the secrecy of the
key not the secrecy of the algorithm
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Contdhellip
Cryptography study of encryption principlesmethods
Cryptanalysis (code breaking) the study of principles methods of deciphering cipher text without knowing key
Cryptology the field of both cryptography and cryptanalysis
Contd
1048708 Unconditional security No matter how much computer power is
available the cipher cannot be broken since the cipher text provides insufficient information to uniquely determine the corresponding plaintext
Computational security Given limited computing resources (eg time
needed for calculations is greater than age of universe) the cipher cannot be broken
Conventional Encryption Principles
1048708 An encryption scheme has five ingredients
1048708 Plaintext 1048708 Encryption algorithm 1048708 Secret Key 1048708 Cipher text 1048708 Decryption algorithm 1048708 Security depends on the secrecy of the
key not the secrecy of the algorithm
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Contd
1048708 Unconditional security No matter how much computer power is
available the cipher cannot be broken since the cipher text provides insufficient information to uniquely determine the corresponding plaintext
Computational security Given limited computing resources (eg time
needed for calculations is greater than age of universe) the cipher cannot be broken
Conventional Encryption Principles
1048708 An encryption scheme has five ingredients
1048708 Plaintext 1048708 Encryption algorithm 1048708 Secret Key 1048708 Cipher text 1048708 Decryption algorithm 1048708 Security depends on the secrecy of the
key not the secrecy of the algorithm
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Conventional Encryption Principles
1048708 An encryption scheme has five ingredients
1048708 Plaintext 1048708 Encryption algorithm 1048708 Secret Key 1048708 Cipher text 1048708 Decryption algorithm 1048708 Security depends on the secrecy of the
key not the secrecy of the algorithm
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Cryptology
Classified along three independent dimensions 1)Type of encryption operations used for transforming plaintext to cipher text substitution transposition product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption
3)Way in which plaintext is processed1048708 Block1048708 stream
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Cryptanalysis
Two general approaches to attack an encryption scheme
1) Cryptanalysis needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher
text pair
2) Brute-Force attack1048708 attacker tries every possible key to decrypt1048708 needs to check so many keys
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Types of Cryptanalysis
1048708 Ciphertext only1048708 attacker only knows the encryption algorithm amp
ciphertext 1048708 Known plaintext1048708 knows the encryption algorithm amp ciphertext1048708 additionally knows some sample plaintext-
ciphertext pairs 1048708 Chosen plaintextattacker selects plaintext and obtain ciphertext to
attack cipher 1048708 Chosen ciphertext1048708 select ciphertext and obtain plaintext to attack
cipher
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Classical Ciphers
Where letters of plaintext are replaced by other letters or by numbers or symbols
Or if plaintext is viewed as a sequence of bits then substitution involves replacing plaintext bit patterns with cipher text bit patterns
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Caesar Cipher
1048708 Earliest known substitution cipher 1048708 Devised by Julius Caeser 1048708 First attested use in military affairs 1048708 Replaces each letter by 3rd letter of alphabets 1048708 Example 1048708 Plaintext MEET ME AFTER THE TEA PARTY Cipher text PHHW PH DIWHU WKH WHD SDUWB
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Contdhellip
1048708 We can generalize Caesar cipher as 1048708 C = E( p) = ( p + k) mod (26) 1048708 p = D(C) = (C ndash k) mod (26) 1048708 Where k is the offset eg 3 as in our example 1048708 p is the letter to be converted into
cipher text and C is cipher text
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Cryptanalysis of Caeser Cipher 1048708 Only have 26 possible ciphers 1048708 A maps to ABZCould simply try each in turn ie usinga brute force search Given cipher text just try all shifts ofletters
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
CAUTION QUIZ AHEAD
You are free to leave the class room but if seated then please
be silent If eyes tried to tilt to fellows paper either for
correction or for soliciting info will cancel you quiz on immediate basis Exams also checks ability honesty zeal and struggle
towards problem solving attitude Initial thesis ldquoeveryone is honest unless he proves
himself otherwiserdquo Hope that initial conditions (thesis) will remain steady
state
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
QUIZ NO 01 1048708 Find the plain text and Key from
the given cipher text 1048708 Cipher Text 1048708 TUSBCMRK MW HMWLSRIWXC
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Attacks Services and Attacks Services and MechanismsMechanisms
Security Attack Any action that compromises the security of information
Security Mechanism A mechanism that is designed to detect prevent or recover from a security attack
Security Service A service that enhances the security of data processing systems and information transfers A security service makes use of one or more security mechanisms
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Security AttacksSecurity Attacks
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
CIPHERS
Now we will discuss various ciphers and their working
Cipher is an algorithm that provides encryption to your data
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Transposition Ciphers
now consider classical transposition or permutation ciphers
these hide the message by rearranging the letter order
without altering the actual letters used can recognise these since have the
same frequency distribution as the original text
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Rail Fence cipher
write message letters out diagonally over a number of rows
then read off cipher row by row eg write message out as
m e m a t r h t g p r y
e t e f e t e o a a t
giving ciphertextMEMATRHTGPRYETEFETEOAAT
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Row Transposition Ciphers
a more complex scheme write letters of message out in rows
over a specified number of columns then reorder the columns according to
some key before reading off the rowsKey 3 4 2 1 5 6 7Plaintext a t t a c k p o s t p o n e d u n t i l t w o a m x y zCiphertext TTNAAPTMTSUOAODWCOIXKNLYPETZ
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Product Ciphers
ciphers using substitutions or transpositions are not secure because of language characteristics
hence consider using several ciphers in succession to make harder but two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes
a new much harder cipher this is bridge from classical to modern ciphers
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Rotor Machines
before modern ciphers rotor machines were most common product cipher
were widely used in WW2 German Enigma Allied Hagelin Japanese Purple
implemented a very complex varying substitution cipher
used a series of cylinders each giving one substitution which rotated and changed after each letter was encrypted
with 3 cylinders have 263=17576 alphabets
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Steganography
an alternative to encryption hides existence of message
using only a subset of letterswords in a longer message marked in some way
using invisible ink hiding in LSB in graphic image or sound file
has drawbacks high overhead to hide relatively few info
bits
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
Summary
have considered classical cipher techniques and
terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography
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