Anthropic Mythos AI Discovers Cryptographic Weaknesses in NIST Post-Quantum Candidate Hawk and Reduced-Round AES

Anthropic reported that its Claude Mythos Preview model produced two new cryptanalytic results, detailed in a company blog post and accompanying technical papers 1. Working with a human researcher over roughly 60 hours, Mythos found a previously unexploited lattice symmetry in HAWK-256, a NIST round-three post-quantum signature candidate that had survived two rounds of expert human review over two years, reducing key-recovery cost from roughly 2^64 to 2^38 operations, cutting the scheme's effective key strength in half and requiring key sizes to double to restore the original security level 12. Working largely autonomously, Mythos separately devised a technique called "Mobius Bridge" that made the strongest known meet-in-the-middle attack on seven-round AES-128 between 200 and 800 times faster, under a chosen-plaintext model requiring roughly 2^105 queries, though validating the result's correctness then took Anthropic researchers nearly a month, longer than the discovery itself 13. Anthropic said it disclosed the HAWK finding to the scheme's designers in June and coordinated public release with the NIST mailing list, and stated neither result affects deployed systems 12. The Hacker News reported Anthropic's published HAWK-256 attack code runs in about three hours 42 minutes on a 96-core server 4.