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Transcript of Tomáš Foltýnek [email protected] Faculty of Business and Economics Steganography. CyberWars...
![Page 1: Tomáš Foltýnek foltynek@pef.mendelu.cz Faculty of Business and Economics Steganography. CyberWars Tomas Foltynek Department of Informatics Faculty of Business.](https://reader030.fdocuments.net/reader030/viewer/2022032516/56649c775503460f9492c979/html5/thumbnails/1.jpg)
Tomáš Foltýnek
Facultyof Business and Economics
Steganography. CyberWars
Tomas Foltynek
Department of Informatics
Faculty of Business and Economics
Mendel University in Brno
Czech republic
![Page 2: Tomáš Foltýnek foltynek@pef.mendelu.cz Faculty of Business and Economics Steganography. CyberWars Tomas Foltynek Department of Informatics Faculty of Business.](https://reader030.fdocuments.net/reader030/viewer/2022032516/56649c775503460f9492c979/html5/thumbnails/2.jpg)
Steganography
What is steganography
• Part of cryptology• Art/science about hiding the very existence of
message• Word origin from Greek
– Stegos = hidden– Graphein = write
• Hidden message doesn’t attract attention– No need to encrypt– Combination of steganography and cryptology
ensures discreetness and security
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Steganography
Using steganograpghy
• In countries, where cryptography is illegal• When we want to hide the existence of
message• Secret services – monitoring people
– printer tracking dots• Private companies – copyright protection
– WoW – hidden information in screenshots
![Page 4: Tomáš Foltýnek foltynek@pef.mendelu.cz Faculty of Business and Economics Steganography. CyberWars Tomas Foltynek Department of Informatics Faculty of Business.](https://reader030.fdocuments.net/reader030/viewer/2022032516/56649c775503460f9492c979/html5/thumbnails/4.jpg)
Steganography
Steganography v antiquity
• Salamis battle (480 B.C.)– Persians were about to attack Greece– Greek Damaratus hid a message under wax on empty
tables– Greeks won
• Mesage in hair (described by Herodotos)– Histiaios wanted to encourage Aristagor of Milet to revolt
against Persians– Shaved messenger‘s hair, tattooed a message, waited
until hair grew backg, then sent the messenger• Romans
– Secret inks based on fruit juice or milk
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Steganography
Steganography in middle ages
• Ancient China– message on silk in wax bullet– messenger swallowed
• Giovanni Porta (16. century)– special ink– write message to egg, boil– message penetrates the shell to
eggwhite
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Steganography
Boer war
• Lord Robert Baden-Powell– founder of scout movement
• Needed to draw a plan of boerean artillery configuration
• For the case of capture, plan had to be discrete
• Drawed a meadow with butterflies• Butterfles encoded artillery objects
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Steganography
Twentieth century
• WW2– microdots– null messages
• messages without real meaning• carry just hidden message• messages in radio, etc.
– Common paranoia led to ban of sending newspaper clippings, flowers and childrens‘ drawings
• Digital steganography– new opportunities
![Page 8: Tomáš Foltýnek foltynek@pef.mendelu.cz Faculty of Business and Economics Steganography. CyberWars Tomas Foltynek Department of Informatics Faculty of Business.](https://reader030.fdocuments.net/reader030/viewer/2022032516/56649c775503460f9492c979/html5/thumbnails/8.jpg)
Steganography
N O T I C E
Upper people try catching star kites. Do Indians ask at far trains? Attach asterisk to any of error file. Add last byte.
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Steganography
N O T I C E
Upper people try catching star kites. Do Indians ask at far trains? Attach asterisk to any of error file. Add last byte.
![Page 10: Tomáš Foltýnek foltynek@pef.mendelu.cz Faculty of Business and Economics Steganography. CyberWars Tomas Foltynek Department of Informatics Faculty of Business.](https://reader030.fdocuments.net/reader030/viewer/2022032516/56649c775503460f9492c979/html5/thumbnails/10.jpg)
Steganography
Second letters
• „Apparently neutral's protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affects pretext for embargo on by-products, ejecting suets and vegetable oils.“
• Used by German spy• PERSHING SAILS FROM NY JUNE 1
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Steganography
Digital Steganography
• Any data can serve as a carrier• Human senses mustn’t notice a message
• Hiding to text• Hiding to images• Hiding to audio files• Hiding to video files• Hiding to executables
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Steganography
Hiding to formatted text
• Using different fonts• Bacon cipher
– Francis Bacon (1561-1626)– Carrier 5 times longer than a message– Carrier written by two fonts– SOME TWENTY FIVE
LETTERS HERE
A = AAAAA N = ABBAA
B = AAAAB O = ABBAB
C = AAABA P = ABBBA
D = AAABB Q = ABBBB
E = AABAA R = BAAAA
F = AABAB S = BAAAB
G = AABBA T = BAABA
H = AABBB U + V = BAABB
I + J = ABAAA W = BABAA
K = ABAAB X = BABAB
L = ABABA Y = BABBA
M = ABABB Z = BABBB
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Steganography
What is cryptology
• Science of Cryptography and cryptanalysis• Cryptography
– science of secret codes, enabling the confidentiality of communication through an insecure channel
– e.i. how to make a message uncomprehensible for unauthorised persons• Cryptanalysis
– theory of (in)security analysis of cryptographic systems– e.i. how to break ciphers and read secret messages
• Also includes Steganography & Steganalysis– how to hide a message– how to find a hidden message
• Word origin from Greek: crypto = hidden
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Steganography
The Paradigms of Cryptography
• Confidentiality– the content of a message remains secret– information should’n leak to third party
• Data integrity– to avoid any malicious data manipulation
• insertion, deletion, substitution
• Authentication– identification of the author– signature authentication, access control, etc.
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Steganography
Other Goals of Cryptography
• Authorisation– confirmation about data origin
• Non-repudiation– nobody can deny previous action
• Practical notions– Anonymity, electronic payment, electronic
votes, zero-knowledge protocol,…
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Steganography
Where to use cryptography?
• Internet banking• Phone calls• Paid TV• Multi-user OS• Business• Communication with the government
• Love letters
• Quizzes, games, etc.
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Steganography
Cryptographic methods
• Transposition– change the position of letters– letters remain the same
• Substitution– position of letters remain the same– letters in the message are changed
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Steganography
Transposition
• The position of letters is changed• Example:
IWSAYNMNAERG – TAMNADAYYAAOIAIGOBTEE – NKNDMYHSATAAADNHRLVDHMOMYNW – HTMIETEEIEWOYUAKOBTEAEFNAELE – YHNMOANBLE
• Solution:It was many and many a year agoIn a kingdom by the seaThat a maiden there lived whom you may knowBy the name of Annabel Lee
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Steganography
Scytale (Sparta)
• First military cipher in history• Leather tape wound on a pole of given
thickness
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Steganography
Substitution
• The letters are changed• Codes
– binary code– Morse code
• Ciphers– Alphabet shifting (Caesar cipher)– Polyalfabetic substitution (Vigenère
cipher)
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Steganography
Let’s play a game…
• Make groups of three– Alice– Bob– Eve (sitting between Alice and Bob)
• First round– Eve shuts her ears– Alice and Bob agree on the way of coding– Eve can hear from now on– Alice sends a message to Bob– Eve tries to understand this message
• Second round– Eve can hear all the communication from the beginning– Alice and Bob agree on the way of coding (Eve hears them)– Bob has to send a message secretly to Alice
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Steganography
General encryption process
• Sender applies encryption algorithm to a plain text• S/he gains a cipher text, sends it to the receiver• Recipient applies decryption algorithm to the
cipher text• S/he gains the plain text again
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Steganography
Division of Cryptography
• Symmetric cryptography– both sender and recipient have the same key– deciphering is an inversion of enciphering
• Asymmetric cryptography– sender and recipient have different keys– mathematic relation– algorithms are generally different– useful for both encryption and digital signature
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Steganography
Modular arithmetics
• Arithmetics on a cyclic set
• 2 + 3 = 5 (mod 7)• 5 + 4 = 2 (mod 7)• 5 · 4 = 6 (mod 7)
– because 20/7 = 2, remainder 6• 11 · 9 = 1 (mod 7)
– because 99/7 = 14, remainder 1• 35 = 5 (mod7)
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Steganography
XOR operation
• eXclusive OR• Logical OR, only one of two given expression can
be true– 0 0 = 0– 0 1 = 1– 1 0 = 1– 1 1 = 0
• Sum modulo 2• Simple enciphering and deciphering
C = M K, M = C K
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Steganography
Kerckhoffs’ principle
• Basic cryptographic principle• Dutch lingvist Auguste Kerckhoffs von
Nieuwenhoff (1883)
“A cryptosystem is secure even if everything about the system, except the key, is public knowledge”
• Security shouldn’t depend on the secrecy of algorithm, but on the secrecy of the key
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Steganography
Cryptology in Antiquity
• Hebrew scholars (600 to 500 BC)– Atbash cipher
• The battle of Salamis (480 BC)– message hidden under wax on empty tables
• The revolat against Persians– The message tattooed to the shaved head of a slave,
hiddeb by regrown hair • China
– message writen on silk in a wax bullet, messenger swallowed the bullet…
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Steganography
Caesar Cipher
• Alphabet shifted by 3abcdefghijklmnopqrstuvwxyzDEFGHIJKLMNOPQRSTUVWXYZABC
• Example– veni, vidi, vici YHQL, YLGL, YLFL
• Algorithm: alphabet shift• Key: by how many letters
– 25 possible keys (English)
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Steganography
Improvements of Caesar Cipher
• Unsorted cipher alphabetabcdefghijklmnopqrstuvwxyzJULISCAERTVWXYZBDFGHKMNOPQ
• More than 41010 possibilities• Monoalphabetic substitution cipher• Kryptanalysis via frequency analysis
– found by arabic theologists
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Steganography
Monoalphabetic cipher improvements
• Zero letters– no meaning, change frequency
• Code words• Homophonic substitution cipher
– each letter has more representations according to its frequency
– polygram frequency analysis
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Steganography
Vigenère cipher
• Polyalphabetic substitutioncipher
• 1586 Blaise de Vigenère• Enciphering:
– Key WHITEWHITEWHITEWHITEWHI– Plain text diverttroopstoeastridge– Cipher text ZPDXVPAZHSLZBHIWZBKMZNM
• Usage of tabula recta– sum mod 26
• Unbroken for 300 years
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Steganography
Breaking Vigenère cipher
• Charles Babbage (1791 – 1891)– Inventor of Difference Engines– Ciphers as a hobby
• Kasiski examintaion – guessing key lengthKINGKINGKINGKINGKINGKINGthesunandthemaninthemoonDPRYEVNTNBUKWIAOXBUKWWBT
• Guessing the key– divide message to groups enciphered by the same
letter– shifted alphabet – frequency analysis
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Steganography
The unbreakable cipher
• Problem of Vigenère cipher: repeating– we need a sequence of random letters– same length as the message
• One time pad cipher– Gilbert Vernam (1890 – 1960)– unbreakability proved by C. Shannon– key distribution problem, practically
useless
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Steganography
Why was a computer invented?
• New inventions mostly come of– human laziness– wars
• First computer– 1943 Colossus– Great Britain, Bletchley Park– Breaking German ENIGMA code
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Steganography
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Steganography
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Steganography
Breaking the Enigma
• Poland – Marian Rejewski– codebooks for day key inference
from repeated message key– mechanical decipherer – “bomb”
• Alan Turing (1912 – 1954)– Inventor of Turing machine,
founder of the theory of computation– Analysed plenty of messages
• given structure (weather info)
– New type of “bomb” guessing the key from ciphertext and supposed plaintext
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Steganography
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Steganography
Computers in Cryptology
• Breaking ciphers = trying huge amount of possibilities– computer does this in quite short time– the end of “classical” ciphers
• One-way functions– computation of every input
in polynomial time– computation of inverse in
exponential time– P != NP problem
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Steganography
Symmetric encryption algorithms
• DES, 3DES, AES, IDEA– Block ciphers– Many rounds consisting of transpositions, permutations,
substitutions, XOR with key, etc.• Security depends on the key length
– Let’s consider 128 bit key– 2128 possible values– 1GHz processor: 230 operations per second– Breaking time: 298 seconds– The age of the Universe: 260 seconds– 1 more bit => breaking time doubles
• Problem: How to distribute the key?
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Steganography
Data Encryption Standard
• Block symmetric cipher• 1973 – 1974 Horst Fiestel• 16 rounds, Fiestel funciton
– expansion, XOR, substitution, permutation• Better methods
than brute force attack are known
• 3DES– good for the
present
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Steganography
Advanced Encryption Standard
• Block symmetric cipher• 4 steps:
– AddRoundKey– SubByte– ShiftRows– MixColumns
• NSA top secret
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Steganography
Key exchange algorithm
• 1976 Diffie, Hellman, Merkle• One-way function Yx (mod P)
– if we know the result, Y and P, it‘s infeasible to compute x• How to generate a common value
– Alice and Bob agree on Y and P• via untrusted channel => Y and P are publicly known
– Each of them has his/her own x• denoted A for Alice and B for Bob
– Alice counts α = YA (mod P), Bob counts β = YB (mod P)– Alice and Bob exchange α and β– Alice counts kA = βA (mod P), Bob counts kB = αB (mod P)
– Since kB = kA, both of them know the value of the key
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Steganography
Asymmetric cryptography: RSA
• A pair of keys is needed• How to generate a keypair
– choose two distinct prime numbers p,q– compute n = p·q– compute φ(n) = φ(p)·φ(q) = (p-1)·(q-1)– choose an integer e (1<e<φ(n); GCD(e,φ(n)) = 1)– determine an integer d such that d·e 1 (mod φ(n))
• The public key is the pair (n,e)• The private key is the pair (n,d)• It’s impossible to determine one key from another without
knowing p,q• Try to
– count 13*37– factorize 527
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Steganography
RSA enciphering and deciphering
• Enciphering– c = me mod n
• Deciphering– m = cd mod n
• Proof of correctness– cd (me)d me·d (mod n)– Because e·d 1 (mod p-1) and e·d 1 (mod q-1) – Then e·d m (mod p-1) and e·d m (mod q-1)– Therefore med m1 (mod p·q) ... Euler‘s theorem– And finally cd m (mod n)
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Steganography
Using RSA for Encryption and Digital Signature
• Using RSA for encryption– Sender encrypts the message with receiver’s public key
(everyone can do this)– Only receiver is able to decrypt the message (s/he is the
only one having private key)• Using RSA for digital signature
– Author encrypts the message (hash) with his own private key (only he can do this)
– Anybody can examine his/her authorship by decrypting the message by author’s public key
• Combination (encryption and signature)– Sender encrypts the message both with receiver’s public
key and his own private key– Only receiver can decrypt the message and examine
authorship
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Steganography
Digital signature scheme
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Steganography
Verification of the Digital Signature
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Steganography
Public key certification I.
• Let’s imagine Alice wants to send a secret and signed message to Bob
• Eve stands between them and controls the whole communication
• Eve substitutes Alice’s public key with hers– Bob has Eve’s public key considering it as Alice’s
• Eve substitutes Bob’s public key with her (another) key– Alice has Eve’s public key considering it as Bob’s
• Neither Alice nor Bob know the real owner of the key• Eve can then control and change the whole
communication considered to be secret.
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Steganography
Public key certification II.
• Solution: Public key certification• Certification authority (CA) verifies key
owner’s identity• Certification = digitally signed message
saying “This key belongs to Alice”• We need to trust the certification authority• CAs are certified by the government• CAs watch their confidentiality because of
business
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Steganography
Bypassing cryptography
• Cryptanalysis stands behind cryptography• “Unbreakable” ciphers are known
– Meant unbreakable in reasonable time• Electromagnetic tapping
– Messages are captured before encryption– Tapping can be shielded; In USA special
permission from FBI is required• Viruses, Trojan horses
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Steganography
Steganography
• Hiding the existence of the message• Hiding messages to almost all file types is possible
– Images, Music, Video, Executables, Text, …
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Steganography
Sources
• Literature– Simon Singh: The Code Book– David Kahn: The Codebreakers– Serge Vaudenay: A Classical Introduction to
Cryptography: Applications for Communications Security
• Internet– computer.howstuffworks.com/computer-internet-
security-channel.htm– en.wikipedia.org/wiki/Category:Computer_security– www.stegoarchive.com– Google
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Steganography
The end
• Thank you for your attention• Questions?