1

CRYPTOGRAPHY

PRESENTED BY : NILAY JAYSWAL

BRANCH : COMPUTER SCIENCE & ENGINEERING

ENTRY NO. : 14BCS033

2OVERVIEW

Cryptography Vocabulary Encryption and Decryption Transmission Technique Symmetric Cryptography Asymmetric Cryptography Conclusion

3What is Cryptography ?

Cryptography is the science of using mathematics to encrypt and decrypt data.

Benefit ?

Cryptography enables you to store sensitive information or transmit it across insecure networks so that it cannot be read by anyone except the intended recipient.

4VOCABULARY

Plaintext: Data that can be read and understood without any special measures.

Encryption: The method of disguising plaintext in such a way as to hide its substance is called encryption.

Cipher text: Encrypting plaintext results in unreadable gibberish called cipher text.

Decryption: The process of reverting cipher text to its original plaintext is called decryption.

Key: some secret piece of information that customizes how the cipher text is

5…continued

Cryptanalysis: The art of breaking ciphers, i.e. retrieving the plaintext without knowing the proper key.

Cryptographers: People who do cryptography Cryptanalysts: Practitioners of cryptanalysis. Cryptology: The branch of mathematics that studies

the mathematical foundations of cryptographic methods.

Cipher: The Encoder

6ENCRYPTION & DECRYPTION

• encryptionplaintext

• decryptionciphertex

t

plaintext

7Why Cryptography ?

For “secret writing” To establish a shared secret when other people

(eavesdroppers) are listening.

Types of Cryptography

1. Symmetric key cryptography

2. Asymmetric key cryptography

8Transmission Technique

Sender

Plaintext in Encoder

Ciphertext out Eavesdroppe

r

Ciphertext in Decoder

Plaintext in Receiver

9CLASSIFICATION

Cryptography

Symmetric Key Cryptography

Asymmetric Key

Cryptograph

10Symmetric

Key Cryptography

Classical Approach

Modern Approach

Classical Approach

Transposition Cipher

Substitution Cipher

Modern Approach

Stream Cipher Block Cipher

11SYMMETRIC KEY CRYPTOGRPHY

Symmetric Key Cryptography are algorithms for that use the same key for both  encryption of plaintext and decryption of ciphertext. They may be identical or there may be a simple transformation to go between the two.

Plai

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Encr

yption

Ke

y “

X “

Cip

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Dec

rypt

ion

Key

“ X ”

Plai

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12TRANSPOSITION CIPHER

In classical cryptography, a transposition cipher changes one character from the plaintext to another

i.e. the order of the characters is changed

e.g.

1 2 3 4 5 6 7 8 9

Plaintext : T O P S E C R E T

Ciphertext : 2 1 4 3 5 7 6 8 9

O T S P E R C T E

13SUBSTITUTION CIPHER

Substitution cipher is a method of encryption by which units of plaintext are substituted with

ciphertext according to a regular system.

e.g.

Plaintext : A B C D X Y Z

Ciphertext : A B C D E F X Y Z

14STREAM CIPHER

A Stream Cipher is a symmetric or secret-key encryption algorithm that encrypts a single bit at a time. With a Stream Cipher, the same plaintext bit or byte will encrypt to a different bit or byte every time it is encrypted.

e.g. :Plain text: Pay 100Binary of plain text : 010111101 (hypothetical)Key : 100101011

Perform XORCipher text : 110010110

15BLOCK CIPHER

Block cipher technique involves encryption of one block of text at a time. Decryption also takes one block of encrypted text at a time. Length of the block is usually 64 or 128 bits.

e.g. :

Plain text : four and five

Four and five

Key Key Key

wvfa ast wvfe

Ciphertext : wvfa ast wvfe

16ASYMMETRIC KEY CRYPTOGRAPHY

Asymmetric Key Cryptography is an asymmetric scheme that uses a Pair of keys for encryption: a Public key, which encrypts data, and a corresponding Private key (secret key) .

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Encr

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: Pu

blic

Key

Cip

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Dec

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: Pr

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e ke

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Plai

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17CRYPTANALYSIS

Cryptanalysis refers to the study of ciphers, cipher text, or cryptosystems (that is, to secret code systems) with a view to finding weaknesses in them that will permit retrieval of the plain text from the cipher text, without necessarily knowing the key or the algorithm. This is known as breaking the cipher, cipher text, or cryptosystem.

Unlike cryptography which is a clearly defined science, Cryptanalysis is as much an art as it is a science.

18Cryptanalysis Techniques

Known - plain text analysis

Chosen – plain text analysis (Differential cryptanalysis)

Cipher text - only analysis

Man – in – the - middle attack

19ACOUSTIC CRYPTANALYSIS

It is a side channel attack which exploits sounds emitted by computers or machines.

Modern acoustic cryptanalysis mostly focuses on sounds emitted by computer keyboards and internal computer components

Historically it has also been applied to impact printers and electromechanical cipher machines.

20CONCLUSION

Cryptography, being an art of encrypting and decrypting confidential information and private messages, should be implemented in the network security to prevent any leakage and threat.

It can be done by using any of these techniques discussed above for fortifying the personal data transmission as well as for secure transaction.

Acoustic cryptanalysis, being an art of decrypting or leaking confidential information from the sound generated from the CPU, Keyboard, printers, etc may be used in both constructive as well as destructive

21REFERENCE

Yang, Sarah (14 September 2005), "Researchers recover typed text using audio recording of keystrokes", UC Berkeley News.

Adi Shamir & Eran Tromer. "Acoustic cryptanalysis". Blavatnik School of Computer Science, Tel Aviv University. Retrieved 1 November 2011.

http://en.wikipedia.org/wiki/Cryptography https://www.coursera.org/course/crypto

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THANK YOU…

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Q & A