Add support for EdDSA/Minisign signatures to sign-hash/sign-file, also add support for choosing credential algorithm to make-credential

[stevenwdv]

This adds support for EdDSA pre-hashed signatures to sign-file (solokeys/solo#397), possibly including a trusted comment according to Minisign.

New sign-file flags:

  --minisign                Use Minisign-compatible signatures (pre-hashed)
  --sig-file TEXT           Destination file for signature
                            (<filename>.(mini)sig if empty)
  --trusted-comment TEXT    Trusted comment included in global signature
                            (combine with --minisign) [default: <time and file
                            name, prehashed>]
  --untrusted-comment TEXT  Untrusted comment not included in global signature
                            (combine with --minisign and --sig-file)
                            [default: signature created on solokey]
  --key-id TEXT             Key ID to write to signature file (8 bytes as HEX)
                            (combine with --minisign and --sig-file) [default:
                            <hash of credential ID>]

If the --minisign flag is passed, the signature will using pre-hashing with Blake2b-512 instead of SHA-256 and the signature file will be a Minisign-compatible signature. The flag can only be used with EdDSA credentials.

To be able to choose the credential type, I added the following flag to make-credential:

  --alg TEXT                Algorithm(s) for key, separated by ',', in order
                            of preference  [default: EdDSA,ES256]

To view supported algorithms, use the new solo key list-algorithms command.

make-credential now also supports saving Minisign keys for EdDSA credentials, and it prints the public key:

  --no-pubkey               Do not display public key
  --minisign                Display public key in Minisign-compatible format
  --key-file TEXT           File to store public key (use with --minisign)
  --key-id TEXT             Key ID to write to key file (8 bytes as HEX) (use
                            with --key-file) [default: <hash of credential ID>]
  --untrusted-comment TEXT  Untrusted comment to write to public key file (use
                            with --key-file) [default: <key ID>]

Breaking change: the credential_id parameter is now assumed to be a HEX credential, to make it consistent with make-credential.

More info, mostly about an earlier version using a FIDO2 extension instead of a custom CTAP command, can be found in solokeys/solo#575.

See solokeys/solo#583 for the authenticator PR.