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Tomáš Foltýnek foltynek@pef.mendelu.cz Faculty of Business and Economics Steganography. CyberWars Tomas Foltynek Department of Informatics Faculty of Business and Economics Mendel University in Brno Czech republic

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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

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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

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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.

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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.

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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 = AAAAAN = ABBAA B = AAAABO = ABBAB C = AAABAP = ABBBA D = AAABBQ = ABBBB E = AABAAR = BAAAA F = AABABS = BAAAB G = AABBAT = BAABA H = AABBBU + V = BAABB I + J = ABAAAW = BABAA K = ABAABX = BABAB L = ABABAY = BABBA M = ABABBZ = 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 – TAMNADAYYAAO IAIGOBTEE – NKNDMYHSA TAAADNHRLVDHMOMYNW – HTMIETEEIEWOYUAKO BTEAEFNAELE – YHNMOANBLE Solution: It was many and many a year ago In a kingdom by the sea That a maiden there lived whom you may know By 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 3 5 = 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 3 abcdefghijklmnopqrstuvwxyz DEFGHIJKLMNOPQRSTUVWXYZABC 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 alphabet abcdefghijklmnopqrstuvwxyz JULISCAERTVWXYZBDFGHKMNOPQ More than 4 10 10 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 substitution cipher 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 length KINGKINGKINGKINGKINGKING thesunandthemaninthemoon DPRYEVNTNBUKWIAOXBUKWWBT 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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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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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 –2 128 possible values –1GHz processor: 2 30 operations per second –Breaking time: 2 98 seconds –The age of the Universe: 2 60 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 Y x (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 = Y A (mod P), Bob counts β = Y B (mod P) –Alice and Bob exchange α and β –Alice counts k A = β A (mod P), Bob counts k B = α B (mod P) –Since k B = k A, 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

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Steganography RSA enciphering and deciphering Enciphering –c = m e mod n Deciphering –m = c d mod n Proof of correctness –c d (m e ) d m e·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 m ed m 1 (mod p·q)... Euler‘s theorem –And finally c d 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 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?

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Section 2.1: Shift Ciphers and Modular Arithmetic Practice HW from Barr Textbook (not to hand in) p.66 # 1, 2, 3-6, 9-12, 13, 15.

Section 2.1: Shift Ciphers and Modular Arithmetic Practice HW from Barr Textbook (not to hand in) p.66 # 1, 2, 3-6, 9-12, 13, 15.

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