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// Copyright The Notary Project Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package signature
import (
"crypto"
"crypto/ecdsa"
"crypto/rsa"
"crypto/x509"
"fmt"
)
// Algorithm defines the signature algorithm.
type Algorithm int
// Signature algorithms supported by this library.
//
// Reference: https://github.com/notaryproject/notaryproject/blob/main/specs/signature-specification.md#algorithm-selection
const (
AlgorithmPS256 Algorithm = 1 + iota // RSASSA-PSS with SHA-256
AlgorithmPS384 // RSASSA-PSS with SHA-384
AlgorithmPS512 // RSASSA-PSS with SHA-512
AlgorithmES256 // ECDSA on secp256r1 with SHA-256
AlgorithmES384 // ECDSA on secp384r1 with SHA-384
AlgorithmES512 // ECDSA on secp521r1 with SHA-512
)
// KeyType defines the key type.
type KeyType int
const (
KeyTypeRSA KeyType = 1 + iota // KeyType RSA
KeyTypeEC // KeyType EC
)
// KeySpec defines a key type and size.
type KeySpec struct {
// KeyType is the type of the key.
Type KeyType
// KeySize is the size of the key in bits.
Size int
}
// Hash returns the hash function of the algorithm.
func (alg Algorithm) Hash() crypto.Hash {
switch alg {
case AlgorithmPS256, AlgorithmES256:
return crypto.SHA256
case AlgorithmPS384, AlgorithmES384:
return crypto.SHA384
case AlgorithmPS512, AlgorithmES512:
return crypto.SHA512
}
return 0
}
// ExtractKeySpec extracts KeySpec from the signing certificate.
func ExtractKeySpec(signingCert *x509.Certificate) (KeySpec, error) {
switch key := signingCert.PublicKey.(type) {
case *rsa.PublicKey:
switch bitSize := key.Size() << 3; bitSize {
case 2048, 3072, 4096:
return KeySpec{
Type: KeyTypeRSA,
Size: bitSize,
}, nil
default:
return KeySpec{}, &UnsupportedSigningKeyError{
Msg: fmt.Sprintf("rsa key size %d bits is not supported", bitSize),
}
}
case *ecdsa.PublicKey:
switch bitSize := key.Curve.Params().BitSize; bitSize {
case 256, 384, 521:
return KeySpec{
Type: KeyTypeEC,
Size: bitSize,
}, nil
default:
return KeySpec{}, &UnsupportedSigningKeyError{
Msg: fmt.Sprintf("ecdsa key size %d bits is not supported", bitSize),
}
}
}
return KeySpec{}, &UnsupportedSigningKeyError{
Msg: "unsupported public key type",
}
}
// SignatureAlgorithm returns the signing algorithm associated with the KeySpec.
func (k KeySpec) SignatureAlgorithm() Algorithm {
switch k.Type {
case KeyTypeEC:
switch k.Size {
case 256:
return AlgorithmES256
case 384:
return AlgorithmES384
case 521:
return AlgorithmES512
}
case KeyTypeRSA:
switch k.Size {
case 2048:
return AlgorithmPS256
case 3072:
return AlgorithmPS384
case 4096:
return AlgorithmPS512
}
}
return 0
}
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