Anthropic says Claude identified the timestamp-based generation of NIST ECDSA curve seeds and partially explained several base points.

Anthropic says an internal research model, Claude, identified the origin of the long-debated seed values behind several NIST ECDSA curves, finding they were generated from a weak C library pseudorandom number generator seeded by Unix timestamps. The company said the finding closes a years-long mystery around a widely used cryptographic standard and does not indicate a cryptographic break or new weakness in ECDSA.

In a post published Friday, 16 October 2026, Anthropic said the NIST P-192, P-224, P-256, P-384 and P-521 seeds were not hashes of hidden phrases, as some researchers had suspected, but outputs of the C library's lrand48 generator. According to the post, the generator was initialized with a Unix timestamp and sampled to produce 20-byte candidates, with the published seed corresponding to one candidate in the sequence. Anthropic said Claude recovered the seeds in under half an hour after an employee asked the model to explain how they were generated.

The company said the P-256 seed matched candidate 1842 from a run starting on 1997-08-16 01:52:34 UTC, while the other prime-curve seeds matched timestamps between May 1997 and April 1998. Anthropic also said the four binary-curve initializations read as February 1984 when recovered directly, and as April 17, 1998 when the timestamp was doubled, suggesting the software may have halved the clock. The company said that for the ten prime-curve seeds, each recovered srand48 initialization corresponded to a Unix timestamp in that 1997-1998 window.

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