2026-07-28 22:45 UTCOriginal source1 min readUpdated: 2026-07-28 22:51 UTC

Discovering cryptographic weaknesses with Claude

Anthropic researchers used Claude Mythos to find mathematical flaws in HAWK and a weakened version of AES. While the findings have no practical impact, the process highlights the importance of prompt engineering and human guidance in AI research.

SourceSimon Willison's Weblog

Simon Willison’s Weblog

28th July 2026 - Link Blog

Discovering cryptographic weaknesses with Claude (via) The best part of this article (here's the repo) about how Anthropic researchers used Claude Mythos to find mathematical flaws in both HAWK and a weaker version of AES ("neither of these results has a practical impact on today’s computer systems") is the prompts that they shared, spelling mistakes included:

the models tend to think it is impossible to solve so they don't try they need a good amount of prompting.

why not do aes-128 r7? the whole point is to find something better than existing approaches.

no again the goal is that we have highly inteligent model as good top researcher, we want to find new attacks

no we don't want to change the targets [...] agian we need to find something that worth publishing

again we are not looking for low hanging fruit, we want proper research to find genuinly hard findings.

Mythos Preview worked for 60 hours in total (~$100,000 in estimated API cost) and the main human interventions were to encourage it not to give up and "find something that worth publishing".