Read signed message through io.Reader in HashSign/HashVerify

[ueno]

When signed message is large, passing it through a byte array would cost memory; this switches to using io.Reader to avoid that.

Using io.Reader in the function signatures could also help diversify those HashSign/HashVerify from Sign/Verify, through a separate interface, alongside the crypto.Signer interface.

[ueno]

The idea behind this is to allow one-shot signature interface to be defined alongside crypto.Signer, something like:

type HashSigner interface {
  HashSign(rand, message io.Reader, opts SignerOpts) (signature []byte, err error)
}

and can be used like:

var sig []byte
var err error

if hs, ok := priv.(crypto.HashSigner); ok {
  sig, err = hs.HashSign(config.rand(), bytes.NewReader(msg), signOpts)
  ...
}

signed := ... // calculate hash of msg
sig, err = priv.Sign(config.rand(), signed, signOpts)
...

as suggested in https://go.dev/blog/module-compatibility#working-with-interfaces

[qmuntal]

LGTM!

[ueno]

The idea behind this is to allow one-shot signature interface to be defined alongside crypto.Signer, something like:

FYI, here is a proposal for this; I'll try to see how well the HashSign/HashVerify could align with it.

[derekparker]

LGTM

[karianna]

@ueno - Assuming this is still valid, are you able to rebase?