1. CSE 5/7353 – January 25 th 2006 Cryptography

2. Conventional Encryption Shared Key Substitution Transposition

3. 5 Types Cryptanalysis

4. Strength of Cipher Unconditionally Secure Computationally Secure

5. Steganography List Types

6. General Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations

7. Caesar Cipher

8. Caesar Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations

9. Letter Substitution

10. Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations

11. Play Fair Cipher

12. Play Fair Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations

13. Vigenere Cipher

14. Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations

15. Vernam Cipher

16. Vernam Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations

17. Transposition Ciphers

18. Transposition Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations

19. Rotor Machines

20. Rotor Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations

21. Shannon

22. Diffusion –Plain Text “Smearing” –Not Permutation Confusion –Key Obfuscation

23. Feistel Cipher

24. Fiestel Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations

25. Modern Ciphers

26. DES Currently the most widely used block cipher in the world IBM’s LUCIFER was the precursor One of the largest users of the DES is the banking industry, particularly with EFT Although the standard is public, the design criteria used are classified

27. DES Security Recent analysis has shown that DES is well designed (diffusion & confusion) Rapid advances in computing speed though have rendered the 56 bit key susceptible to exhaustive key search –1999 in 22hrs! –3 DES DES also theoretically broken using Differential or Linear Cryptanalysis In practice, unlikely to be a problem yet

28. Overview of DES Encryption Basic process consists of: –An initial permutation (IP) –16 rounds of a complex key dependent calculation F –A final permutation, being the inverse of IP

29. 64-bit key (56-bits + 8-bit parity) 16 rounds Initial permutation Round 1 Round 2 Round 16 56-bit key Final permutation … + F L i – 1 R i – 1 R i K i L i Each Round

30. DES Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations

31. Advanced Encryption Standard AES

32. Origins of AES In 1999, NIST issued a new standard that said 3DES should be used –168-bit key length –Algorithm is the same as DES 3DES had drawbacks –Algorithm is sluggish in software –Only uses 64-bit block size

33. Origins of AES (Cont’d) In 1997, NIST issued a CFP for AES –security strength >= 3DES –improved efficiency –must be a symmetric block cipher (128-bit) –key lengths of 128, 192, and 256 bits

34. Origins of AES (cont’d) First round of evaluation –15 proposed algorithms accepted Second round –5 proposed algorithms accepted Rijndael, Serpent, 2fish, RC6, and MARS Final Standard - November 2001 –Rijndael selected as AES algorithm

35. The AES Cipher Block length is 128 bits Key length is 128, 192, or 256 bits NOT a Feistel structure Processes entire block in parallel during each round using substitutions and permutations The key that is provided as input is expanded Array of forty-four 32-bit words (w[i]) Four distinct words serve as round key (128 bits)

36. Decryption Not identical to encryption Equivalent structure exists May need different implementations if encryption and decryption are needed Quite often only encryption needed –Digest

37. AES Cipher Characteristics Key Size Transposition / Substitution Block / Stream Avalanche Effect Surviving Plain Text Structure – Attacks Historical Uses Practical Observations