Bitcoin's quantum plan assumes some algorithms break. AI just weakened one in 60 hours

Anthropic's AI model Claude Mythos Preview has discovered a significant cryptanalytic weakness in HAWK, a proposed post-quantum digital signature scheme designed to replace current web and banking signatures vulnerable to quantum computers. The AI-driven attack reduced the required computational effort to break HAWK's smallest key parameter from about 2^64 operations to roughly 2^38 operations. This effectively halves the key strength and undermines the attractiveness of HAWK’s smallest key sizes, while compensating by doubling key sizes reduces its efficiency benefits. The attack took approximately 60 hours and cost around $100,000 in computing resources.

HAWK has not been deployed in practice and is not among the quantum-resistant schemes considered for Bitcoin’s migration. Bitcoin and Ethereum currently use elliptic curve signatures, which remain unaffected by this new attack. Bitcoin’s quantum-resistant proposal, BIP-360, relies on three algorithms already standardized by NIST and emphasizes the use of multiple options to guard against future cryptanalytic advances. However, the improved speed of classical attacks, as demonstrated by Anthropic’s AI, underscores the urgency of moving toward quantum-resistant cryptography. BIP-361, another proposal related to Bitcoin’s quantum migration, highlights a closing window for migration due to accelerating attack improvements.

In addition to weakening HAWK, Anthropic’s AI also achieved notable improvements in attacking a deliberately weakened version of AES, the industry-standard encryption cipher widely used to secure wallet files, achieving speedups between 200 to 800 times. Against Poseidon, a hash function important in zero-knowledge proof systems used for privacy protocols and rollups, the model’s improvements were more modest, under tenfold. Claude initially declined the AES challenge but succeeded after iterative prompting, highlighting both the complexity and potential of AI in cryptanalysis.

These findings arrive just as the privacy-focused cryptocurrency Zcash implemented an upgrade aimed at maintaining recoverability against future quantum computers, illustrating the real-time pressure on cryptographic schemes to withstand both classical and quantum advances. Anthropic coordinated disclosure of the HAWK attack with its authors and NIST’s public mailing list to ensure transparency and encourage timely responses. Overall, these developments emphasize how AI is rapidly accelerating classical cryptanalysis, influencing the crypto industry’s preparations for a quantum future.