package awskms import ( "crypto" "crypto/ecdsa" "crypto/rsa" "io" "github.com/aws/aws-sdk-go/service/kms" "github.com/pkg/errors" "go.step.sm/crypto/pemutil" ) // 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 { return kms.SigningAlgorithmSpecRsassaPssSha256, nil } return kms.SigningAlgorithmSpecRsassaPkcs1V15Sha256, nil case crypto.SHA384: if isPSS { return kms.SigningAlgorithmSpecRsassaPssSha384, nil } return kms.SigningAlgorithmSpecRsassaPkcs1V15Sha384, nil case crypto.SHA512: if isPSS { return kms.SigningAlgorithmSpecRsassaPssSha512, nil } return kms.SigningAlgorithmSpecRsassaPkcs1V15Sha512, nil default: return "", errors.Errorf("unsupported hash function %v", h) } case *ecdsa.PublicKey: switch h := opts.HashFunc(); h { case crypto.SHA256: return kms.SigningAlgorithmSpecEcdsaSha256, nil case crypto.SHA384: return kms.SigningAlgorithmSpecEcdsaSha384, nil case crypto.SHA512: return kms.SigningAlgorithmSpecEcdsaSha512, nil default: return "", errors.Errorf("unsupported hash function %v", h) } default: return "", errors.Errorf("unsupported key type %T", key) } }