International Association
for Cryptologic Research

In this paper, we present a new efficient stand-alone MAC construct named SMAC, based on processing using the Finite State Machine (FSM) part of the stream cipher family SNOW, which in turn uses the AES round function. It offers a combination of very high speed in software and hardware with a truncatable tag. Three concrete base versions of SMAC are proposed, each offering a different security level. SMAC can also be directly integrated with an external ciphering engine in an AEAD mode. Every design decision is thoroughly justified and supported by the results of our cryptanalysis and simulations. Additionally, we introduce an aggregated mode version, SMAC-1xn, in which software performance reaches up to 925 Gbps (around 0.038 cycles per byte) for long messages in a single thread. To the best of our knowledge, SMAC achieves a record-breaking software performance compared to all known MAC engines.

In Addition-Rotation-Xor (ARX) ciphers, the large domain size obstructs the application of the boomerang connectivity table. In this paper, we explore the problem of computing this table for a modular addition and the automatic search of boomerang characteristics for ARX ciphers. We provide dynamic programming algorithms to efficiently compute this table and its variants. These algorithms are the most efficient up to now. For the boomerang connectivity table, the execution time is 42(n − 1) simple operations while the previous algorithm costs 82(n − 1) simple operations, which generates a smaller model in the searching phase. After rewriting these algorithms with boolean expressions, we construct the corresponding Boolean Satisfiability Problem models. Two automatic search frameworks are also proposed based on these models. This is the first time bringing the SAT-aided automatic search techniques into finding boomerang attacks on ARX ciphers. Finally, under these frameworks, we find out the first verifiable 10-round boomerang trail for SPECK32/64 with probability 2−29.15 and a 12-round trail for SPECK48/72 with probability 2−44.15. These are the best distinguishers for them so far. We also perceive that the previous boomerang attacks on LEA are constructed with an incorrect computation of the boomerang connection probability. The result is then fixed by our frameworks.