Comparison AES-Rijndael/Serpent 2G1704: Internet Security and Privacy Weltz Max 2G1704: Internet Security and Privacy Weltz Max

Outline Historical perspective Description of AES-Rijndael Description of Serpent Comparison Historical perspective Description of AES-Rijndael Description of Serpent Comparison

Historical perspective 1998 Advanced Encryption Standard contest 1999 Serpent and Rijndael among the last 5 finalist algorithms –Along with Mars, RC6 and Twofish 2000 Rijndael selected as AES algorithm 1998 Advanced Encryption Standard contest 1999 Serpent and Rijndael among the last 5 finalist algorithms –Along with Mars, RC6 and Twofish 2000 Rijndael selected as AES algorithm

Main elements –Parameters Key size: 128, 160, 192, 224, 256bits Block size: 128, 160, 192, 224, 256bits Number of rounds: 6+max(Bs,Ks) –Operations  Two substitutions tables Rearrangement of octets Key schedule Main elements –Parameters Key size: 128, 160, 192, 224, 256bits Block size: 128, 160, 192, 224, 256bits Number of rounds: 6+max(Bs,Ks) –Operations  Two substitutions tables Rearrangement of octets Key schedule Description of Rijndael

Description of Rijndael State array –Size of Bs –Organized in 4- octet columns State array –Size of Bs –Organized in 4- octet columns

Description of Rijndael Rounds 1.Octets through the S-Box 2.Rows shifted 3.Columns mixed Rounds 1.Octets through the S-Box 2.Rows shifted 3.Columns mixed

Description of Rijndael Key expansion –As many round as required –Obtain (Nr+1)Bs/32 columns Key expansion –As many round as required –Obtain (Nr+1)Bs/32 columns

What is AES-Rijndael? AES’ recommendations for Rijndael –Block size: 128-bits –Key size: 128bits -> AES-128 -> 10 rounds 196bits -> AES-196 -> 12 rounds 256bits -> AES-256 -> 14 rounds AES’ recommendations for Rijndael –Block size: 128-bits –Key size: 128bits -> AES-128 -> 10 rounds 196bits -> AES-196 -> 12 rounds 256bits -> AES-256 -> 14 rounds

Description of Serpent Parameters –Key size: 128, 192, 256 bits 128 and 192bit keys are padded with 100… –Block size: 128bits –Number of rounds: rounds are supposedly enough Operations –  –8 substitution tables (S-boxes) –Linear transformation –Key schedule Parameters –Key size: 128, 192, 256 bits 128 and 192bit keys are padded with 100… –Block size: 128bits –Number of rounds: rounds are supposedly enough Operations –  –8 substitution tables (S-boxes) –Linear transformation –Key schedule

Description of Serpent Process –Initial permutation –32 Rounds –Final permutation Permutations –Statically defined –Simplifying the optimized implementation Process –Initial permutation –32 Rounds –Final permutation Permutations –Statically defined –Simplifying the optimized implementation

Description of Serpent Rounds 1.Key mixing 2.Pass through S-box 3.Linear transformation Except for the last round –(  33rd subkey) Rounds 1.Key mixing 2.Pass through S-box 3.Linear transformation Except for the last round –(  33rd subkey)

Description of Serpent Linear transformation –Left-rotations –  ’ing –Left-shifts Linear transformation –Left-rotations –  ’ing –Left-shifts Source: Wikipedia

Description of Serpent Key expansion –Padding (100…) –Affine expansion –S-boxes –Collapsing Key expansion –Padding (100…) –Affine expansion –S-boxes –Collapsing

Comparison Process Security Hardware performance Software performance Process Security Hardware performance Software performance

Comparison: Process RijndaelSerpent Round 10x 12x 14x S-boxes Raw shifting Columns mixed  Round Key 31x Key mixing S-boxes Linear t. Final t. Key mixing S-boxes Key mixing Adapted from [Lutz02]

Comparison: Security RijndaelSerpent Margins (rounds) 6 insecure 10/12/14 suggested AES 15 insecure 17 suggested Authors 16: secure 32 suggested Best known attacks (2006) 7/8/9 rounds11 rounds Comments Known side channel attacks (timing) Better than or equivalent to any other 128bit block cipher Old design

Comparison: Hardware Rijndael 88.5MHz –Assets Small number –Of rounds –Of subkeys Identical rounds –Drawbacks Variable number of rounds Key length matters Large S-boxes Rijndael 88.5MHz –Assets Small number –Of rounds –Of subkeys Identical rounds –Drawbacks Variable number of rounds Key length matters Large S-boxes Serpent 122.9MHz –Assets Fixed number of rounds Key lengths does not matter Small S-boxes –Drawbacks Different S-Box types Larger number –Of rounds –Of subkeys No hardware shared between encryption and decryption Serpent 122.9MHz –Assets Fixed number of rounds Key lengths does not matter Small S-boxes –Drawbacks Different S-Box types Larger number –Of rounds –Of subkeys No hardware shared between encryption and decryption

Comparison: Software RijndaelSerpent Encryption1276 | 440/ | 1030/900 Decryption Performance (see figures) –Serpent 2 to 6 times slower Non-symmetrical performances But stable performances when changing architecture Performance (see figures) –Serpent 2 to 6 times slower Non-symmetrical performances But stable performances when changing architecture Pentium 133Mhz MMX | Pentium Pro C/Pentium Pro ASM

Conclusion Rijndael chosen by AES: why? –Fastest for small blocks and hashes encryption –Second fastest for bulk encryption But –Security issues In 1999, Schneier et al. claimed there was no possible timing attacks against Rijndael… In 2006, a timing attack is found –Serpent is more secure if you are ready to spend more time Rijndael chosen by AES: why? –Fastest for small blocks and hashes encryption –Second fastest for bulk encryption But –Security issues In 1999, Schneier et al. claimed there was no possible timing attacks against Rijndael… In 2006, a timing attack is found –Serpent is more secure if you are ready to spend more time

Questions Opposition

Sources Network Security, Private Communication in a Public World, C. Kaufman, R. Perlman, M. Speciner, 2002 Wikipedia’s articles (French and English) on Rijndael, Bitwise operators, AES process and Serpent Cryptographic Hardware and Embedded Systems, Pawel Chodowiec, 2002 Network Security, Private Communication in a Public World, C. Kaufman, R. Perlman, M. Speciner, 2002 Wikipedia’s articles (French and English) on Rijndael, Bitwise operators, AES process and Serpent Cryptographic Hardware and Embedded Systems, Pawel Chodowiec, 2002 Serpent, a Proposal for the AES, R. Anderson, E. Biham, L. Knudsen, 1998 Serpent homepage [Lutz02]2Gbit/s Hardware Realizations of RIJNDAEL and SERPENT: A Comparative Analysis, Lutz, Treichler, G ü rkaynak, Kaeslin, Basler, Erni, Reichmuth, Rommens, Oetiker, Fichtner, 2002 Serpent, a Proposal for the AES, R. Anderson, E. Biham, L. Knudsen, 1998 Serpent homepage [Lutz02]2Gbit/s Hardware Realizations of RIJNDAEL and SERPENT: A Comparative Analysis, Lutz, Treichler, G ü rkaynak, Kaeslin, Basler, Erni, Reichmuth, Rommens, Oetiker, Fichtner, 2002

Sources (cont.) A Note on Comparing AES Candidates (Revised), Biham, 1998 (?) Performance Comparison of the AES Submissions, B. Schneier, J. Kelsey, D. Whiting, D. Wagner, C. Hall, N. Ferguson, 1999 Performance Evaluation fo the AES Finalists on the High- End Smart Card, F. Sano, M. Koike, S. Kawamura, M. Shiba, 2000 A Note on Comparing AES Candidates (Revised), Biham, 1998 (?) Performance Comparison of the AES Submissions, B. Schneier, J. Kelsey, D. Whiting, D. Wagner, C. Hall, N. Ferguson, 1999 Performance Evaluation fo the AES Finalists on the High- End Smart Card, F. Sano, M. Koike, S. Kawamura, M. Shiba, 2000 Performance Comparison of 5 AES Candidates with New Performance Evaluation Tool, M. Takenaka, N. Torii, K. Itoh, J. Yajima, 2000 Instruction-level Parallelism in AES Candidates, C.S.K. Clapp, 1999 How Well Are High-End DSPs Suites for the AES Algorithms, T. J. Wollinger, M. Wang, J. Guajardo, C. Paar, 2000 Performance Comparison of 5 AES Candidates with New Performance Evaluation Tool, M. Takenaka, N. Torii, K. Itoh, J. Yajima, 2000 Instruction-level Parallelism in AES Candidates, C.S.K. Clapp, 1999 How Well Are High-End DSPs Suites for the AES Algorithms, T. J. Wollinger, M. Wang, J. Guajardo, C. Paar, 2000

Comments Non-exhaustive listing and extracts of sources are available here: – DRkjSwoQiJ-sle4hhttp:// DRkjSwoQiJ-sle4h Interesting links for both Serpent and Rijndael (and others) can be found here: – Figures where realized specially for this presentation, except stated otherwise Non-exhaustive listing and extracts of sources are available here: – DRkjSwoQiJ-sle4hhttp:// DRkjSwoQiJ-sle4h Interesting links for both Serpent and Rijndael (and others) can be found here: – Figures where realized specially for this presentation, except stated otherwise