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package cose
import (
"crypto"
"crypto/ecdsa"
"crypto/ed25519"
"crypto/rsa"
"errors"
"fmt"
)
// Verifier is an interface for public keys to verify COSE signatures.
type Verifier interface {
// Algorithm returns the signing algorithm associated with the public key.
Algorithm() Algorithm
// 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
Verify(content, signature []byte) error
}
// NewVerifier returns a verifier with a given public key.
// Only golang built-in crypto public keys of type `*rsa.PublicKey`,
// `*ecdsa.PublicKey`, and `ed25519.PublicKey` are accepted.
func NewVerifier(alg Algorithm, key crypto.PublicKey) (Verifier, error) {
switch alg {
case AlgorithmPS256, AlgorithmPS384, AlgorithmPS512:
vk, ok := key.(*rsa.PublicKey)
if !ok {
return nil, fmt.Errorf("%v: %w", alg, ErrInvalidPubKey)
}
// RFC 8230 6.1 requires RSA keys having a minimun size of 2048 bits.
// Reference: https://www.rfc-editor.org/rfc/rfc8230.html#section-6.1
if vk.N.BitLen() < 2048 {
return nil, errors.New("RSA key must be at least 2048 bits long")
}
return &rsaVerifier{
alg: alg,
key: vk,
}, nil
case AlgorithmES256, AlgorithmES384, AlgorithmES512:
vk, ok := key.(*ecdsa.PublicKey)
if !ok {
return nil, fmt.Errorf("%v: %w", alg, ErrInvalidPubKey)
}
if !vk.Curve.IsOnCurve(vk.X, vk.Y) {
return nil, errors.New("public key point is not on curve")
}
return &ecdsaVerifier{
alg: alg,
key: vk,
}, nil
case AlgorithmEd25519:
vk, ok := key.(ed25519.PublicKey)
if !ok {
return nil, fmt.Errorf("%v: %w", alg, ErrInvalidPubKey)
}
return &ed25519Verifier{
key: vk,
}, nil
default:
return nil, ErrAlgorithmNotSupported
}
}
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