certificates/kms/awskms/signer.go

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package awskms
import (
"crypto"
"crypto/ecdsa"
"crypto/rsa"
"io"
"github.com/aws/aws-sdk-go/service/kms"
"github.com/pkg/errors"
"github.com/smallstep/cli/crypto/pemutil"
)
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// Signer implements a crypto.Signer using the AWS KMS.
type Signer struct {
service KeyManagementClient
keyID string
publicKey crypto.PublicKey
}
// NewSigner creates a new signer using a key in the AWS KMS.
func NewSigner(svc KeyManagementClient, signingKey string) (*Signer, error) {
keyID, err := parseKeyID(signingKey)
if err != nil {
return nil, err
}
// Make sure that the key exists.
signer := &Signer{
service: svc,
keyID: keyID,
}
if err := signer.preloadKey(keyID); err != nil {
return nil, err
}
return signer, nil
}
func (s *Signer) preloadKey(keyID string) error {
ctx, cancel := defaultContext()
defer cancel()
resp, err := s.service.GetPublicKeyWithContext(ctx, &kms.GetPublicKeyInput{
KeyId: &keyID,
})
if err != nil {
return errors.Wrap(err, "awskms GetPublicKeyWithContext failed")
}
s.publicKey, err = pemutil.ParseDER(resp.PublicKey)
return err
}
// Public returns the public key of this signer or an error.
func (s *Signer) Public() crypto.PublicKey {
return s.publicKey
}
// Sign signs digest with the private key stored in the AWS KMS.
func (s *Signer) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) ([]byte, error) {
alg, err := getSigningAlgorithm(s.Public(), opts)
if err != nil {
return nil, err
}
req := &kms.SignInput{
KeyId: &s.keyID,
SigningAlgorithm: &alg,
Message: digest,
}
req.SetMessageType("DIGEST")
ctx, cancel := defaultContext()
defer cancel()
resp, err := s.service.SignWithContext(ctx, req)
if err != nil {
return nil, errors.Wrap(err, "awsKMS SignWithContext failed")
}
return resp.Signature, nil
}
func getSigningAlgorithm(key crypto.PublicKey, opts crypto.SignerOpts) (string, error) {
switch key.(type) {
case *rsa.PublicKey:
_, isPSS := opts.(*rsa.PSSOptions)
switch h := opts.HashFunc(); h {
case crypto.SHA256:
if isPSS {
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return kms.SigningAlgorithmSpecRsassaPssSha256, nil
}
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return kms.SigningAlgorithmSpecRsassaPkcs1V15Sha256, nil
case crypto.SHA384:
if isPSS {
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return kms.SigningAlgorithmSpecRsassaPssSha384, nil
}
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return kms.SigningAlgorithmSpecRsassaPkcs1V15Sha384, nil
case crypto.SHA512:
if isPSS {
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return kms.SigningAlgorithmSpecRsassaPssSha512, nil
}
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return kms.SigningAlgorithmSpecRsassaPkcs1V15Sha512, nil
default:
return "", errors.Errorf("unsupported hash function %v", h)
}
case *ecdsa.PublicKey:
switch h := opts.HashFunc(); h {
case crypto.SHA256:
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return kms.SigningAlgorithmSpecEcdsaSha256, nil
case crypto.SHA384:
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return kms.SigningAlgorithmSpecEcdsaSha384, nil
case crypto.SHA512:
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return kms.SigningAlgorithmSpecEcdsaSha512, nil
default:
return "", errors.Errorf("unsupported hash function %v", h)
}
default:
return "", errors.Errorf("unsupported key type %T", key)
}
}