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Cybersecurity cyberlab3
- 1. Cryptology DUH BRX UHDGB? Slidesby Raymond Borges 1
- 2. Outline • Background • Ancient Cryptography • Frequency Analysis • Modern Cryptography • Secure Communication • Tools of the trade • Conclusion 2
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- 5. The Ancient Artof Secret Messages 5
- 6. Background Principles and methodsfor: 1. Transforming message into unintelligible 2. Transforming message back to original form 6
- 7. Background Principles and methodsfor: • Retransforming message back to original form • Without knowledge of key 7
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- 9. Encryption • Plaintext: Thisis what you want to encrypt • Ciphertext: The encrypted output • Enciphering or encryption: process which converts plaintext to ciphertext • Encryption algorithm: Sequence processing steps to transform plaintext into ciphertext • Secret key: Sets some or all parameters used by encryption algorithm 9
- 10. Practice (transposition) Caesar Cipher Ciphertext:DUH BRX UHDGB Solution: c = E(k, p) = (p + k) mod 26 c = E(3, p) = (p + 3) mod 26 for k=key=3 4 mod 26 = 4 so A=D p = D(k, c) = (c − k) mod 26 D=4 (4-3) mod 26 = 1 10
- 11. Practice (substitution) Monoalphabetic cipher •plaintext letters: a b c d e f ..... • substitution letters: t h i j a b ..... Key is sequence of substitution letters 26 ! = 4.03291461 × 1026 Impossible to crack? No…. Polyalphabetic tougher… 11
- 12. ETAOIN SHRDLU (Frequencyanalysis) • ‘E’ is the most common letter in the English language, • ‘Th’ is the most common bigram • ‘The’ most common trigram • Letter frequency English 12
- 13. Frequency analysis • Mostfrequently occurring trigrams ordered by decreasing frequency are: 13
- 14. Polyalphabetic Ciphers • The Vigenère cipher • First letter use key 1 • Second uses key 2 • Third uses key 3 To Decrypt go backwards 14
- 15. Modern Cryptography Data EncryptionStandard (DES) 1976 • 64 bit key (uses 56bits) • 16 stages • Block divided into two 32-bit halves • XOR • Subkeys made key schedule 15
- 16. Modern Cryptography Feistel function: 1.Expansion- the 32-bit half-block is expanded to 48 bits by duplicating half of the bits 2. Key mixing — the result is combined with a subkey using an XOR operation. 3. Substitution —block divided into eight 6-bit pieces then uses substitution boxes 4. Permutation 16
- 17. Modern Cryptography Advanced EncryptionStandard (AES) 2001 • Substitution-permutation network • Not Feistel • Fixed block size 128 bits • Key size of 128, 192, or 256 bits 17
- 18. Modern Cryptography Advanced Encryption Standard (AES) 1. KeyExpansion 2. Initial Round 1. AddRoundKey 3. Rounds 1. SubEytes 2. ShiftRows 3. MixColumns 4. AddRoundKey 4.Final Round 1. SubBytes 2. ShiftRows 3. AddRoundKey 18
- 19. Public-key cryptography RSA- RonRivest, Adi Shamir, Leonard Adleman 1978 • Uses factoring problem (large primes) • Two large primes of similar size > 100 digits Example: Public (n = 3233, e = 17) Private key is (n = 3233, d = 2753) n=p1*p2, e=coprime number to (p1-1)(p2-1) d =modular multiplicative inverse of e 19
- 20. Public-key cryptography Encryption Decryption c = me (mod n) m = cd (mod n) Example: To encrypt m = 65 c = 6517 (mod 3233) = 2790 To decrypt c = 2790, we calculate m = 27902753 (mod 3233) = 65 20
- 21. Secure Communication • AES256 bit key • 15360-bit RSA keys are equivalent 256-bit symmetric keys • 2^256 = 1.15792089 × 1077 brute-force? Use RSA then AES for secure communication HTTPS, SSH, SFTP, SSL and TLS and others 21
- 22. Some Tools ofthe trade File Encryption • Axantum • WinZip Disk encryption • TrueCrypt Network • Open SSH 22
- 23. References • http://www.axantum.com/axcrypt/Downloads .html • http://dottech.org/freeware-reviews/15996/ • http://technet.microsoft.com/en- us/library/cc757819(v=ws.10).aspx 23
- 24. Questions? 24