Claude Mythos Preview finds new cryptanalytic attacks on post-quantum HAWK and 7-round AES
On July 28, 2026 Anthropic reported that Claude Mythos Preview found two new cryptanalysis results. One attack on HAWK, a post-quantum lattice signature scheme in NIST's additional-signatures process, exploits a previously unnoticed automorphism and halves the effective key size (HAWK-256 from 2^64 to 2^38). The other is a 200–800x faster attack on 7-round (reduced-round) AES-128. Neither affects deployed systems, but it is a clear case of an AI model improving the state of the art in cryptanalysis.
Key facts
- HAWK: found in about 60 hours; a nontrivial automorphism in the lattice structure cuts effective key size by a factor of two; HAWK-256 security from 2^64 to 2^38 (per Anthropic)
- HAWK is a candidate, not deployed; restoring security requires roughly doubling key sizes
- AES: new 'Möbius Bridge' fingerprinting algorithm, 200–800x faster than the previous best meet-in-the-middle attack on 7-round AES-128; chosen-plaintext, needs 2^105 plaintexts; full 10-round AES unaffected
- Each result cost roughly $100,000 in API usage (per Anthropic's post)
- Preliminary results: 13-round LEA, 6-round Serpent-128 full key recovery, small improvements on Salsa20, Poseidon and SHA-1
- Disclosure coordinated with US government and industry partners; HAWK authors notified in June 2026
- Cryptographer Matthew Green published commentary on the results (July 29)
Science result
- Field
- computer-science / cryptanalysis
- Problem
- Security of the HAWK post-quantum signature scheme and of reduced-round AES-128
- Result
- Key-size-halving attack on HAWK via a lattice automorphism (HAWK-256: 2^64 to 2^38); 200–800x faster attack on 7-round AES-128
- AI system
- Claude Mythos Preview
- Human role
- AI-assisted: Anthropic researchers ran and checked Mythos Preview's search; the depth of human guidance is not quantified
- Verification
- Company-reported; HAWK authors notified; independent expert commentary (Matthew Green), no peer-reviewed paper found
- Status
- pending
- Why surprising
- HAWK had survived about two years of expert review before the model found the symmetry in roughly 60 hours.
What happened
Anthropic's researchers pointed Claude Mythos Preview at cryptographic primitives. The two headline results are attacks that beat the best published ones: a structural weakness in HAWK and a much faster distinguisher-based attack on 7-round AES. Anthropic stresses that neither breaks anything in production.
Why it matters
Cryptanalysis is a field where progress is rare and highly expert. An AI model producing publishable improvements is evidence that frontier models now contribute to original security research, and it raises the question of how post-quantum candidates should be reviewed from now on.
Unverified: whether the HAWK result has been written up as a paper or acknowledged by NIST was not checked.
Changelog
- 2026-10-01: created (leads run, from the Anthropic uncited-posts audit)
Related events
- Anthropic reveals Claude Mythos Preview, withholds it over cyber risk and launches Project Glasswing ★★★★★
- Anthropic releases Claude Fable 5 and Claude Mythos 5 — first generally available Mythos-class model ★★★★★
Sources (5)
- officialAnthropic: Discovering cryptographic weaknesses with Claude
- discussionMatthew Green: Some thoughts about Anthropic's new cryptanalysis results
- pressThe Quantum Insider: AI finds new weaknesses in cryptographic algorithms
- pressThe Batch: Claude weakens a quantum lock
- pressThe Decoder: Mythos found vulnerabilities in cryptographic algorithms
id: 2026-07-28-claude-mythos-cryptanalysis-hawk-aes · updated 2026-10-01 · open in the interactive timeline