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package cose
import (
"crypto"
"crypto/rsa"
"io"
)
// rsaSigner is a RSASSA-PSS based signer with a generic crypto.Signer.
//
// Reference: https://www.rfc-editor.org/rfc/rfc8230.html#section-2
type rsaSigner struct {
alg Algorithm
key crypto.Signer
}
// Algorithm returns the signing algorithm associated with the private key.
func (rs *rsaSigner) Algorithm() Algorithm {
return rs.alg
}
// Sign signs message content with the private key, using entropy from rand.
// The resulting signature should follow RFC 8152 section 8.
//
// Reference: https://datatracker.ietf.org/doc/html/rfc8152#section-8
func (rs *rsaSigner) Sign(rand io.Reader, content []byte) ([]byte, error) {
hash := rs.alg.hashFunc()
digest, err := computeHash(hash, content)
if err != nil {
return nil, err
}
return rs.key.Sign(rand, digest, &rsa.PSSOptions{
SaltLength: rsa.PSSSaltLengthEqualsHash, // defined in RFC 8230 sec 2
Hash: hash,
})
}
// rsaVerifier is a RSASSA-PSS based verifier with golang built-in keys.
//
// Reference: https://www.rfc-editor.org/rfc/rfc8230.html#section-2
type rsaVerifier struct {
alg Algorithm
key *rsa.PublicKey
}
// Algorithm returns the signing algorithm associated with the public key.
func (rv *rsaVerifier) Algorithm() Algorithm {
return rv.alg
}
// Verify verifies message content with the public key, returning nil for
// success.
// Otherwise, it returns ErrVerification.
//
// Reference: https://datatracker.ietf.org/doc/html/rfc8152#section-8
func (rv *rsaVerifier) Verify(content []byte, signature []byte) error {
hash := rv.alg.hashFunc()
digest, err := computeHash(hash, content)
if err != nil {
return err
}
if err := rsa.VerifyPSS(rv.key, hash, digest, signature, &rsa.PSSOptions{
SaltLength: rsa.PSSSaltLengthEqualsHash, // defined in RFC 8230 sec 2
}); err != nil {
return ErrVerification
}
return nil
}
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