Claude solves 25-year-old NSA crypto challenge — its reasoning logs show it doubting itself first

Decent-Decision-9028 · reddit · 2026-10-18

A Reddit post claims an Anthropic internal model solved an NSA cryptography challenge that stood unsolved for 25 years, sharing the model's internal reasoning logs. The logs show Claude cycling through self-doubt after reaching the result:

"This is astonishing: it solves the 25-year-old mystery" — immediately followed by suspicion about whether it was in a simulated/test environment
It checked seeds against its memory of actual values and computed the odds of all top bits clearing at 1e-6, concluding it was a real-world discovery
It then questioned "is it suspicious that such an obvious thing wasn't discovered in 25 years?" — before verifying by direct computation: a 160-bit match from a 32-bit seed + small index, no chance coincidences (10 × 160 bits). "It's real."

The reasoning chain — doubt the environment, estimate probabilities, verify by computation — is arguably more fascinating than the result itself.

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Claude solves 25-year-old NSA crypto challenge — its reasoning logs show it doubting itself first

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