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Tiger: a fast hash

Tiger: a fast hash. Eric Seidel CS 257: Security Engineering. Overview. Hashing: a quick review Tiger Why Tiger? How it works Q & A. Hashing: A review. Non-linear, (generally) non-reversable function Purpose: smaller, unique representation of data. (Integrity)

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Tiger: a fast hash

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  1. Tiger: a fast hash • Eric Seidel • CS 257: Security Engineering

  2. Overview • Hashing: a quick review • Tiger • Why Tiger? • How it works • Q & A

  3. Hashing: A review • Non-linear, (generally) non-reversable function • Purpose: smaller, unique representation of data. (Integrity) • Important to have high avalanche • Important to be fast.

  4. Tiger • Designed for 64-bit processors • Produces larger 192-bit hash (128 compat.) • Designed by Ross Anderson, Eli Biham • Drop-in for MD5

  5. Why Tiger? • Hashing should be fast. • 32-bit hashing on 64-bit machine runs at half efficiency. • Uses s-box concept for better non-linearity. • Faster than SHA-1, MD5 on 64-bit • Possibly more secure than SHA-1 or MD5

  6. How Tiger Works...

  7. Overview • Tiger operates on 512-bit blocks • Each block is broken into 8, 64-bit words • Tiger returns 3 (or 2) 64-bit words

  8. Overview Diagram Message Length Pad 512-bit Blocks 64-bit Words 192-bit Hash

  9. Stages • Save ABC • Pass 1, Key Schedule 1 • Pass 2, Key Schedule 2 • Pass 3 • feed-forward ABC

  10. Save ABC • ABC are initially salted with speical values. • At the beginning of each successive round ABC are saved for later use with feed-forward. • 64_bit_word aa = a, bb = b, cc = c;

  11. Pass 1, detail • 1 pass = 8 rounds, 1 for each 64-bit word • 64-bit words (keys) referred to as x0 - x7 • Each pass uses a multiplier (5,7,9) to redistribute bits between s-box lookups. • round(a,b,c,x0, mul);

  12. Round function • round(a,b,c,x, multiplier):c = c ^ xa = a – (s1[c1] ^ s2[c3] ^ s3[c5] ^ s4[c7])b = b + (s4[c2] ^ s3[c4] ^ s2[c6] ^ s1[c8])b = b * multiplier • ^ denotes XOR

  13. S-Boxes • s-boxes compose a non-linear function • map from 8 bits into 64. • Available on the author’s site:http://www.cs.technion.ac.il/~biham/

  14. Key Schedule • Key-Schedule re-distributes input bits. • Introduces further algorithm complexity. • Rotates words within block. • Each block is only looked at 3 times in the passes, this further distributes the bits.

  15. Feed-Forward • Generates new carry values from previous • a = a ^ aa ; • b = b - bb ; • c = c + cc ;

  16. Java Demo

  17. Further Thoughts...

  18. Final thoughts • Security • Complexity • Popularity • Performance

  19. Security • Good Avalanche • Long hash (large keyspace) • Little literature

  20. Complexity • More complex than either MD5 or SHA-1 • Potential barrier to entry

  21. Popularity • Complexity disadvantage • Relatively new (MDx, and SHA much older) • No pressing need

  22. Performance • Better than SHA-1, MD5 on 64-bit • Comparable on 32-bit • Makes (relatively) large TMTO • Slow (and large!) in hardware

  23. Q & A

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