Anthropic says Claude found new attacks on HAWK and reduced-round AES

Anthropic said an unreleased version of its Claude Mythos model uncovered two previously unknown cryptographic attacks, including one against HAWK, a post-quantum digital signature scheme now in the third round of the U.S. National Institute of Standards and Technology’s competition. According to the company, Claude identified a symmetry in HAWK’s structure that cuts the cost of recovering a secret key in the smallest configuration from 2^64 operations to 2^38, a roughly 67 million-fold reduction. Anthropic said fixing the issue would require roughly doubling HAWK’s key size, which would undercut the compactness and speed that make the scheme attractive for blockchains and other systems sensitive to signature size. The company also described a separate result on a 7-round research version of AES-128, where Claude was asked to avoid all five established families of AES cryptanalysis and invent a new approach. Anthropic said the model eventually produced a technique called “Möbius Bridge,” reducing one of the nine key bytes an attacker previously needed to guess. It also reported that Claude broke 13 rounds of LEA, though deployed LEA uses 24 rounds. Anthropic said it disclosed the findings to the algorithms’ authors and relevant U.S. government and industry partners before publication, and coordinated the HAWK finding with NIST.