Claude Mythos HAWK attack challenges post-quantum crypto candidate

Anthropic says an unreleased version of its most powerful AI model found new weaknesses in cryptographic systems, making the Claude Mythos HAWK attack a notable development for anyone watching crypto’s long-term security. The immediate impact appears limited: HAWK has not been deployed, according to Decrypt, and Bitcoin still uses ECDSA, a pre-quantum digital signature system.

The broader point is harder to ignore. Crypto networks will eventually need defenses against quantum computers, and the systems meant to replace today’s cryptography need to be tested before they protect real money.

What did Claude Mythos find in HAWK?

Anthropic said Claude Mythos Preview found two previously unknown attacks on cryptographic algorithms. One of those attacks targeted HAWK, a digital signature system designed for the post-quantum era.

A digital signature is the math that proves a transaction was authorized by the holder of a private key without revealing that private key. Post-quantum cryptography refers to systems built to resist future quantum computers, which could threaten some of today’s widely used encryption and signature methods.

HAWK had been advanced by the National Institute of Standards and Technology, or NIST, into the third round of its post-quantum competition in May, according to Decrypt. The same report said HAWK was the last lattice-based candidate remaining in that process.

Anthropic said Claude identified a symmetry in HAWK’s math that had not previously been used by human researchers. That discovery lowered the estimated work needed to steal HAWK’s smallest key from 2^64 operations to 2^38 operations, roughly 67 million times less work, according to Decrypt.

Why does key size matter for blockchains?

Anthropic said fixing HAWK would require roughly doubling key sizes and that doing so “eliminates many of the reasons” the system was attractive. HAWK’s appeal came from compact keys and fast signing, according to Decrypt.

For blockchains, signature size is more than a technical detail. Bigger signatures take up more block space, and block space is the scarce capacity networks use to process transactions. When demand rises, that space can affect fees.

That trade-off matters because any blockchain looking for a quantum-resistant replacement must weigh security, speed and data size. A fix that makes signatures larger can reduce the advantage that made one candidate stand out.

Is Bitcoin or crypto broken?

No current deployment was reported as broken. Decrypt noted that HAWK has not been deployed anywhere and that Bitcoin continues to use ECDSA, the older signature scheme that post-quantum candidates may eventually replace.

The finding does raise a practical concern for the industry. Recent work on quantum defenses, including efforts discussed by firms and crypto developers, depends on the assumption that replacement cryptographic schemes are sound enough to secure future systems.

Anthropic’s result also shows the two-sided role AI may play in security research. The same kind of model that can uncover flaws may also help researchers test and harden systems before they are put into production.

This story draws on original reporting from Decrypt.