The Fast Software Encryption 2005 Workshop was the twelfth in a series of annual workshops on symmetric cryptography, sponsored for the fourth year by the International Association for Cryptologic Research (IACR). The workshop concentratedonallaspectsoffastprimitivesforsymmetriccryptology,including thedesign,cryptanalysisandimplementationofblockandstreamciphersaswell as hash functions and message authentication codes. The ?rst FSE workshop was held in Cambridge in 1993, followed by Leuven in 1994, Cambridge in 1996, Haifain1997,Parisin1998,Romein1999,NewYorkin2000,Yokohamain2001, Leuven in 2002, Lund in 2003, and New Delhi in 2004. This year, a total of 96 submissions were received. After an extensive review by the Program Committee, 30 submissions were accepted. Two of these s- missions were merged into a single paper, yielding a total of 29 papers accepted for presentation at the workshop. Also, we were very fortunate to have in the programan invited talk byXuejia Laion Attacks andProtection ofHash Fu- tions and a very entertaining rump session that Bart Preneel kindly accepted to chair. These proceedings contain the revised versions of the accepted papers; the revised versions were not subsequently checked for correctness.

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New Designs.- A New MAC Construction ALRED and a Specific Instance ALPHA-MAC.- New Applications of T-Functions in Block Ciphers and Hash Functions.- The Poly1305-AES Message-Authentication Code.- Stream Ciphers I.- Narrow T-Functions.- A New Class of Single Cycle T-Functions.- F-FCSR: Design of a New Class of Stream Ciphers.- Boolean Functions.- Cryptographically Significant Boolean Functions: Construction and Analysis in Terms of Algebraic Immunity.- The ANF of the Composition of Addition and Multiplication mod 2 n with a Boolean Function.- Block Ciphers I.- New Combined Attacks on Block Ciphers.- Small Scale Variants of the AES.- Stream Ciphers II.- Unbiased Random Sequences from Quasigroup String Transformations.- A New Distinguisher for Clock Controlled Stream Ciphers.- Analysis of the Bit-Search Generator and Sequence Compression Techniques.- Some Attacks on the Bit-Search Generator.- Hash Functions.- SMASH A Cryptographic Hash Function.- Security Analysis of a 2/3-Rate Double Length Compression Function in the Black-Box Model.- Preimage and Collision Attacks on MD2.- Modes of Operation.- How to Enhance the Security of the 3GPP Confidentiality and Integrity Algorithms.- Two-Pass Authenticated Encryption Faster Than Generic Composition.- Padding Oracle Attacks on CBC-Mode Encryption with Secret and Random IVs.- Stream Ciphers III.- Analysis of the Non-linear Part of Mugi.- Two Attacks Against the HBB Stream Cipher.- Two Linear Distinguishing Attacks on VMPC and RC4A and Weakness of RC4 Family of Stream Ciphers.- Impossible Fault Analysis of RC4 and Differential Fault Analysis of RC4.- Block Ciphers II.- Related-Key Rectangle Attacks on Reduced Versions of SHACAL-1 and AES-192.- New Attacks Against Reduced-Round Versions of IDEA.- Implementations.- How toMaximize Software Performance of Symmetric Primitives on Pentium III and 4 Processors.- A Side-Channel Analysis Resistant Description of the AES S-Box.- DPA Attacks and S-Boxes.