Reasons for the rewrite:
- Migrate away from `ec25519` as our implementation of Ed25519,
because that crate is unmaintained.
Instead of `ec25519` we use `ed25519-dalek` which is the most popular
implementation of Ed25519 in Rust.
- Migrate away from `amplify`, because we make very little use of its
features. Here, we only use `amplify::Bytes32`, which is just a thin
wrapper of `[u8; 32]`.
Instead of `amplify::Bytes32` we use `type PublicKeyBytes = [u8; 32]`.
The realization that `ExtendedSignature` is not really tied to SSH, but
is merely a representation of a key together with a signature, allows to
relax the bounds on traits in `radicle-cob`.
Separating out uses of "public key" (a rather simple model of a key,
just 32 bytes) and "verifying key" (an actual point on the Edwards
curve, ready to verify signatures, using more memory than just 32 bytes)
allows a more sensible definition of `crypto::Signer`, which propagates
to `radicle-cob`, `radicle`, `radicle-cli`, `radicle-node` and
simplifies trait bounds.
In `radicle-node`, make the fact clearer that actually the secret key
itself is required (for our implementation of Diffie-Hellman) not
"just" signing. This results in removal of the generic argument
(usually called `G`) of multiple types.
Concretizing the types in `radicle-node` this way, i.e. by (morally)
setting `G = radicle_crypto::SigningKey`, leads to removal of
`MemorySigner` and `MockSigner`, as they really just wrap a signing
key.
Re-exporting `ed25519::Signature` (via re-export in `ed25519-dalek`)
is hopefully more future-proof than using our own type for signatures.
However, the fact that `ed25519::Signature` is not serializable and
does not implement `std::hash::Hash` means that we have to resort to
ad-hoc solutions in `radicle`:
1. The Identity COB requires serialization of signatures. These are
generally questionable, since the security of the Identity COB
should rely on the security of Signed References. In the medium
term we might even want to consider ignoring signatures in actions.
2. When reading Signed References, detection of Replay Attacks uses
a `HashMap` keyed by signatures. This detection only exists for
backwards compatibility.
These two use cases are exotic enough to warrant ad-hoc implementations.
By not wrapping `ed25519::Signature`, we encourage writing more widely
compatible code in the future.
Co-authored-by: Fintan Halpenny <fintan.halpenny@gmail.com>
