ecdsa: impl signature::hazmat::{PrehashSigner, PrehashVerifier}
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Adds "hazmat" trait impls to `SigningKey` and `VerifyingKey` respectively which allow computing signatures over raw message digests. See RustCrypto/traits#1099. The implementation allows digests which are shorter or longer than the field size of the curve, using zero-padding if the digest is too short, and truncating if it's too long. The minimum digest size is set to half of the curve's field size.
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| cmp::Ordering::Equal => field_bytes.copy_from_slice(prehash), | ||
| cmp::Ordering::Less => { | ||
| // If prehash is smaller than the field size, pad with zeroes | ||
| field_bytes[..prehash.len()].copy_from_slice(prehash); |
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I'm not confident enough but if I read RFC correctly I believe this should be like:
field_bytes[(field_bytes.len()-prehash.len())..].copy_from_slice(prehash);https://datatracker.ietf.org/doc/html/rfc6979#section-2.3.2
otherwise, qlen-blen bits (of value zero) are added to the left of the sequence
the present implementation adds zero on the right so the prehash gets "left shift"'d, while informal description in RFC says:
in many software implementations of arithmetics on big integers, that division is equivalent to a "right shift" by blen-qlen bits.
(Assume this method is intended to use with try_sign_prehashed_rfc6979)
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Opened a PR for this
➡️ #547
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Adds "hazmat" trait impls to
SigningKeyandVerifyingKeyrespectively which allow computing signatures over raw message digests. See RustCrypto/traits#1099.The implementation allows digests which are shorter or longer than the field size of the curve, using zero-padding if the digest is too short, and truncating if it's too long. The minimum digest size is set to half of the curve's field size.