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TRAX, a Tweakable Block Cipher |
/trax |
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Trax is a tweakable block cipher operating on a larger state of 256-bit blocks.
It applies a 256-bit key and 128-bit tweak. To the best of our knowledge, the only
other large tweakable block cipher is Threefish which was used as a building for
the SHA-3 candidate Skein [33]. Unlike this cipher, Trax uses 32-bit words that
are better suited for vectorized implementation as well as on micro-controllers.
Another improvement of Trax over Threefish is the fact that we provide strong
bounds for the probability of all linear trails and all (related-tweak) differential trails.
Because of its Substitution-Permutation Network structure, Trax is
indeed inherently easier to analyze. Such a large tweakable block cipher can provide robust authenticated encryption, meaning that it can retain a high security
level even in case of nonce misuse or in the presence of quantum adversaries, as
argued in [15]. The performance penalty of such guarantees can be minimized
using vectorization and/or parallelism.