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x25519: Ensure serialized privkeys are clamped - #402
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tarcieri
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Oct 25, 2026
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Security audit failure is unrelated
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Currently, X25519 private keys are not serialized in clamped form. This is a violation of the HPKE spec. More details in #401.
This PR resolves #401 and adds a regression test. Technically, HPKE also requires that privkeys be clamped on DEserialization. But we don't actually have to do this. Scalars are always clamped in the
x25519(scalar, point)DH function.This is a breaking API change.