constellation/internal/sigstore/sign.go

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/*
Copyright (c) Edgeless Systems GmbH
SPDX-License-Identifier: AGPL-3.0-only
*/
package sigstore
import (
"bytes"
"crypto"
"crypto/ecdsa"
"crypto/ed25519"
"crypto/rsa"
"crypto/x509"
"encoding/base64"
"encoding/pem"
"errors"
"fmt"
"github.com/secure-systems-lab/go-securesystemslib/encrypted"
"github.com/sigstore/sigstore/pkg/signature"
)
const (
cosignPrivateKeyPemType = "ENCRYPTED COSIGN PRIVATE KEY"
sigstorePrivateKeyPemType = "ENCRYPTED SIGSTORE PRIVATE KEY"
)
// Signer is used to sign the version file. Used for unit testing.
type Signer interface {
Sign(content []byte) (res []byte, err error)
}
// NewSigner returns a new Signer.
func NewSigner(cosignPwd, privKey []byte) Signer {
return signer{cosignPwd: cosignPwd, privKey: privKey}
}
type signer struct {
cosignPwd []byte // used to decrypt the cosign private key
privKey []byte // used to sign
}
func (s signer) Sign(content []byte) (signature []byte, err error) {
signature, err = SignContent(s.cosignPwd, s.privKey, content)
if err != nil {
return signature, fmt.Errorf("sign version file: %w", err)
}
return
}
// SignContent signs the content with the cosign encrypted private key and corresponding cosign password.
func SignContent(password, encryptedPrivateKey, content []byte) ([]byte, error) {
sv, err := loadPrivateKey(encryptedPrivateKey, password)
if err != nil {
return nil, fmt.Errorf("loading private key: %w", err)
}
sig, err := sv.SignMessage(bytes.NewReader(content))
if err != nil {
return nil, fmt.Errorf("signing message: %w", err)
}
return []byte(base64.StdEncoding.EncodeToString(sig)), nil
}
func loadPrivateKey(key []byte, pass []byte) (signature.SignerVerifier, error) {
// Decrypt first
p, _ := pem.Decode(key)
if p == nil {
return nil, errors.New("invalid pem block")
}
if p.Type != cosignPrivateKeyPemType && p.Type != sigstorePrivateKeyPemType {
return nil, fmt.Errorf("unsupported pem type: %s", p.Type)
}
x509Encoded, err := encrypted.Decrypt(p.Bytes, pass)
if err != nil {
return nil, fmt.Errorf("decrypt: %w", err)
}
pk, err := x509.ParsePKCS8PrivateKey(x509Encoded)
if err != nil {
return nil, fmt.Errorf("parsing private key: %w", err)
}
switch pk := pk.(type) {
case *rsa.PrivateKey:
return signature.LoadRSAPKCS1v15SignerVerifier(pk, crypto.SHA256)
case *ecdsa.PrivateKey:
return signature.LoadECDSASignerVerifier(pk, crypto.SHA256)
case ed25519.PrivateKey:
return signature.LoadED25519SignerVerifier(pk)
default:
return nil, errors.New("unsupported key type")
}
}