AI Models Excel at Breaking Classical Ciphers

matthew_d_green · x · 2026-07-20

Cryptography expert Matthew Green shared that after extensive development with Claude and Codex, he found AI coding tools to be among the best at cracking substitution ciphers, homophonic ciphers, and some polyalphabetic ciphers. He also noted that agent instructions in the project README triggered AI safety guardrails, misidentified as red flags.

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