AI Models Break a Cipher, Expose a Proof Error

Five frontier models cracked 6 to 12 previously unbroken cryptographic schemes at full strength, per a benchmark called CryptanalysisBench. Two of those cracks were new to the field: a key-recovery vulnerability in SpoC AEAD and an error in KINDI's security proof. For anyone maintaining or reviewing a custom cipher, that's the review process failing at its one job.

The benchmark ran 191 tasks across six families of cryptographic primitives, posted to arXiv as 2607.18538. It broke 65 to 86 percent of ciphers already known to be broken. Scaled-down versions of the hardest problems fell 24 to 61 times, tested across Claude Opus 4.8, Sonnet 5, Mythos 5, GPT 5.5, and GLM 5.2.

Yes, but reproducing a textbook attack is pattern matching, and that's most of the 65 to 86 percent.

The arXiv post doesn't say whether SpoC AEAD's or KINDI's maintainers have been notified, or whether either flaw holds up outside the benchmark's controlled conditions.