FEATURE/Add: add TRAX-L-17 tweakable block cipher - #508
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Implements TRAX-L-17 (256-bit block, 256-bit key, 128-bit tweak, 17 steps), Aumasson/Beierle et al.'s Alzette-based tweakable block cipher from [BBBGPUV2020]_. Fixes two round-function bugs present in an earlier in-progress draft: the ELL diffusion function used a rotation instead of a true zero-filling left shift for the "v << 16" term, and the post-ELL word shuffle used the wrong permutation of the four branches. Both are corrected to match the designers' reference C code (traxl17_genkeys_ref / traxl17_enc_ref, Appendix D.2 of [BBBGPUV2020]_, also published at https://sparkle-lwc.github.io/trax), and validated bit-for-bit against an independent Python transcription of that reference code since no independently-published numeric test vectors for TRAX-L-17 exist.
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August 24, 2026 11:25
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Summary
TraxBlockCipher(claasp/ciphers/block_ciphers/trax_block_cipher.py), TRAX-L-17 — Beierle, Biryukov, Cardoso dos Santos et al.'s tweakable ARX block cipher from the same paper/family as Alzette and CRAX.traxl17_enc_ref, Appendix D.2 of the eprint):ELL(x) = ROT(x ^ (x << 16), 16)—x << 16is a plain left shift, not a rotation.(x3, x2, x0, x1), not a simple cyclic rotation (the reference C's sequential, not simultaneous, assignments produce a different permutation than a naive reading suggests).Note on test vectors
No officially-published third-party KAT exists for TRAX-L-17 (only source code, no separate KAT appendix/third-party port like CRAX has). Validated against an independent line-by-line Python transcription of the designers' reference C implementation — flagged explicitly as self-derived (not third-party-published) in the class docstring and test file, with the source URL, so a reviewer can re-verify independently.
Test plan
sage -t claasp/ciphers/block_ciphers/trax_block_cipher.py— 10 doctests, all passedpytest -v tests/unit/ciphers/block_ciphers/trax_block_cipher_test.py— 4 passed