This implements https://github.com/dalek-cryptography/ed25519-dalek/issues/64
You can still choose the "prehash" algorithm, as long as it has 64 bytes of
output. Otherwise, everything is hardcoded to use sha2::Sha512. To use a
different implementation you'll need a [patch.crates-io] section in cargo
config.
This caches the public key internally so that we effectively get a free
speedup on key reuse in regular signature verification, similar to that in
batch verification. (However, this also "speeds up"¹ batch verifications.)
¹ Less of a speed up than moving the computation elsewhere, but the speed up
on reuse still also applies to key reuse for batch verification.
Unfortunately the serialised size is likely never going to be the same
as the type's size in memory, as most serialisation formats define
additional headers for parsing safety reasons, such as buffer lengths
and type information.
generic_array v0.12 no longer serializes GenericArray as a Vec,
which reduces the serialized size of PublicKey, Signature, and
SecretKey by 8 bytes. Now that generic_array has been upgraded,
these tests simply ensure the serialization size doesn't change
in the future.
The API for this isn't the greatest and I apologise for that. Suggestions for
improvement welcome. One thing which @hdevalence and I considered was to
change the function signature to:
pub fn verify_batch<D, C, M, S, K>(messages: M,
signatures: S,
public_keys: K,
csprng: &mut C) -> Result<(), SignatureError>
where D: Digest<OutputSize = U64> + Default,
C: Rng + CryptoRng,
M: IntoIterator<Item = &[u8]>,
S: IntoIterator,
S::Item: Borrow<Signature>,
K: IntoIterator,
K::Item: Borrow<Signature>,
The other improvement which could be made is to implement 128-bit scalars for
the randomnesses.
* CLOSES#27
This also simplifies the verification logic. Because the verification check
happens in variable time, we don't need to do a constant-time eq check at the
end, so we can drop the `subtle` dependency entirely.
The `DecodingError` type becomes `SignatureError` and is also used to
signal failing verifications.
This code was significantly based off without boats' error types in
commit 6c1acaca7c, and also upon
conversation with them. Please target them with praise, and blame me
for whatever mistakes I might have made.
