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