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feat(gcpkms): support asymmetric key #1187

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170 changes: 162 additions & 8 deletions gcpkms/keysource.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,8 +2,18 @@ package gcpkms // import "go.mozilla.org/sops/v3/gcpkms"

import (
"context"
"crypto/rand"
"crypto/rsa"
"crypto/sha1"
"crypto/sha256"
"crypto/sha512"
"crypto/x509"
"encoding/base64"
"encoding/pem"
"errors"
"fmt"
"hash"
"hash/crc32"
"os"
"regexp"
"strings"
Expand All @@ -14,6 +24,7 @@ import (
"google.golang.org/api/option"
kmspb "google.golang.org/genproto/googleapis/cloud/kms/v1"
"google.golang.org/grpc"
"google.golang.org/protobuf/types/known/wrapperspb"

"go.mozilla.org/sops/v3/logging"
)
Expand Down Expand Up @@ -103,11 +114,53 @@ func (key *MasterKey) Encrypt(dataKey []byte) error {
}
}()

ctx := context.Background()
purpose, err := key.purpose(ctx, service)
if err != nil {
return err
}

switch purpose {
case kmspb.CryptoKey_ENCRYPT_DECRYPT:
return key.encryptSymmetric(ctx, service, dataKey)
case kmspb.CryptoKey_ASYMMETRIC_DECRYPT:
return key.encryptAsymmetric(ctx, service, dataKey)
default:
log.WithField("resourceID", key.ResourceID).WithField("purpose", purpose.String()).Error("This key is not for encryption")
return fmt.Errorf("this key is not for encryption, purpose: %v", purpose.String())
}
}

func (key *MasterKey) purpose(ctx context.Context, service *kms.KeyManagementClient) (kmspb.CryptoKey_CryptoKeyPurpose, error) {
req := &kmspb.GetCryptoKeyRequest{
Name: key.resourceIDWithoutVersion(),
}
cryptoKey, err := service.GetCryptoKey(ctx, req)
if err != nil {
log.WithError(err).WithField("resourceID", key.ResourceID).Error("Get key metadata failed")
return kmspb.CryptoKey_CRYPTO_KEY_PURPOSE_UNSPECIFIED, fmt.Errorf("failed to get key metadata from GCP KMS service: %w", err)
}

return cryptoKey.GetPurpose(), nil
}

// assume key.ResourceID is in following format
// - `projects/project-id/locations/location/keyRings/keyring/cryptoKeys/key`
// - `projects/project-id/locations/location/keyRings/keyring/cryptoKeys/key/cryptoKeyVersions/version`
func (key MasterKey) resourceIDWithoutVersion() string {
re := regexp.MustCompile(`^(projects/[^/]+/locations/[^/]+/keyRings/[^/]+/cryptoKeys/[^/]+)(?:/cryptoKeyVersions/[^/]+)?$`)
matches := re.FindStringSubmatch(key.ResourceID)
if len(matches) < 2 {
return ""
}
return matches[1]
}

func (key *MasterKey) encryptSymmetric(ctx context.Context, service *kms.KeyManagementClient, dataKey []byte) error {
req := &kmspb.EncryptRequest{
Name: key.ResourceID,
Plaintext: dataKey,
}
ctx := context.Background()
resp, err := service.Encrypt(ctx, req)
if err != nil {
log.WithError(err).WithField("resourceID", key.ResourceID).Error("Encryption failed")
Expand All @@ -117,7 +170,70 @@ func (key *MasterKey) Encrypt(dataKey []byte) error {
// The previous GCP KMS client used to work with base64 encoded
// strings.
key.EncryptedKey = base64.StdEncoding.EncodeToString(resp.Ciphertext)
log.WithField("resourceID", key.ResourceID).Info("Encryption succeeded")
log.WithField("resourceID", key.ResourceID).Info("Symmetric encryption succeeded")
return nil
}

func (key *MasterKey) encryptAsymmetric(ctx context.Context, service *kms.KeyManagementClient, dataKey []byte) error {
req := &kmspb.GetPublicKeyRequest{
Name: key.ResourceID,
}
resp, err := service.GetPublicKey(ctx, req)
if err != nil {
log.WithError(err).WithField("resourceID", key.ResourceID).Error("Get public key failed")
return fmt.Errorf("failed to get public key from GCP KMS service: %w", err)
}

if resp.GetPemCrc32C().GetValue() != wrapperspb.Int64(int64(crc32c([]byte(resp.GetPem())))).Value {
log.WithField("resourceID", key.ResourceID).Error("Get public key response corrupted in-transit")
return errors.New("get public key response corrupted in-transit")
}

block, _ := pem.Decode([]byte(resp.Pem))
publicKey, err := x509.ParsePKIXPublicKey(block.Bytes)
if err != nil {
log.WithError(err).WithField("resourceID", key.ResourceID).Info("Failed to parse public key")
return fmt.Errorf("Failed to parse public key: %w", err)
}
rsaKey, ok := publicKey.(*rsa.PublicKey)
if !ok {
log.WithField("resourceID", key.ResourceID).Info("Public key is not RSA")
return errors.New("public key is not RSA")
}

var hash hash.Hash

switch resp.GetAlgorithm() {
case kmspb.CryptoKeyVersion_RSA_DECRYPT_OAEP_2048_SHA256:
hash = sha256.New()
case kmspb.CryptoKeyVersion_RSA_DECRYPT_OAEP_3072_SHA256:
hash = sha256.New()
case kmspb.CryptoKeyVersion_RSA_DECRYPT_OAEP_4096_SHA256:
hash = sha256.New()
case kmspb.CryptoKeyVersion_RSA_DECRYPT_OAEP_4096_SHA512:
hash = sha512.New()
case kmspb.CryptoKeyVersion_RSA_DECRYPT_OAEP_2048_SHA1:
hash = sha1.New()
case kmspb.CryptoKeyVersion_RSA_DECRYPT_OAEP_3072_SHA1:
hash = sha1.New()
case kmspb.CryptoKeyVersion_RSA_DECRYPT_OAEP_4096_SHA1:
hash = sha1.New()
default:
log.WithField("resourceID", key.ResourceID).WithField("algorithm", resp.GetAlgorithm().String()).Error("Unsupported algorithm")
return fmt.Errorf("Key with unsupported algorithm: %s", resp.GetAlgorithm().String())
}

ciphertext, err := rsa.EncryptOAEP(hash, rand.Reader, rsaKey, dataKey, nil)
if err != nil {
log.WithError(err).WithField("resourceID", key.ResourceID).Error("rsa.EncryptOAEP() error")
return fmt.Errorf("rsa.EncryptOAEP: %w", err)
}

// NB: base64 encoding is for compatibility with SOPS <=3.8.x.
// The previous GCP KMS client used to work with base64 encoded
// strings.
key.EncryptedKey = base64.StdEncoding.EncodeToString(ciphertext)
log.WithField("resourceID", key.ResourceID).Info("Asymmetric encryption succeeded")
return nil
}

Expand Down Expand Up @@ -162,18 +278,51 @@ func (key *MasterKey) Decrypt() ([]byte, error) {
return nil, err
}

ctx := context.Background()

purpose, err := key.purpose(ctx, service)
if err != nil {
return nil, err
}

switch purpose {
case kmspb.CryptoKey_ENCRYPT_DECRYPT:
return key.decryptSymmetric(ctx, service, decodedCipher)
case kmspb.CryptoKey_ASYMMETRIC_DECRYPT:
return key.decryptAsymmetric(ctx, service, decodedCipher)
default:
log.WithField("resourceID", key.ResourceID).WithField("purpose", purpose.String()).Info("This key cannot be used for decryption")
return nil, fmt.Errorf("This key cannot be used for decryption, purpose: %s", purpose.String())
}
}

func (key *MasterKey) decryptSymmetric(ctx context.Context, service *kms.KeyManagementClient, decodedCipher []byte) ([]byte, error) {
req := &kmspb.DecryptRequest{
Name: key.ResourceID,
Ciphertext: decodedCipher,
}
ctx := context.Background()
resp, err := service.Decrypt(ctx, req)
if err != nil {
log.WithError(err).WithField("resourceID", key.ResourceID).Error("Decryption failed")
log.WithError(err).WithField("resourceID", key.ResourceID).Error("Symmetric decryption failed")
return nil, fmt.Errorf("failed to decrypt sops data key with GCP KMS key: %w", err)
}

log.WithField("resourceID", key.ResourceID).Info("Symmetric decryption succeeded")
return resp.Plaintext, nil
}

func (key *MasterKey) decryptAsymmetric(ctx context.Context, service *kms.KeyManagementClient, decodedCipher []byte) ([]byte, error) {
req := &kmspb.AsymmetricDecryptRequest{
Name: key.ResourceID,
Ciphertext: decodedCipher,
}
resp, err := service.AsymmetricDecrypt(ctx, req)
if err != nil {
log.WithError(err).WithField("resourceID", key.ResourceID).Error("Asymmetric decryption failed")
return nil, fmt.Errorf("failed to decrypt sops data key with GCP KMS key: %w", err)
}

log.WithField("resourceID", key.ResourceID).Info("Decryption succeeded")
log.WithField("resourceID", key.ResourceID).Info("Asymmetric decryption succeeded")
return resp.Plaintext, nil
}

Expand Down Expand Up @@ -201,7 +350,7 @@ func (key MasterKey) ToMap() map[string]interface{} {
// It returns an error if the ResourceID is invalid, or if the setup of the
// client fails.
func (key *MasterKey) newKMSClient() (*kms.KeyManagementClient, error) {
re := regexp.MustCompile(`^projects/[^/]+/locations/[^/]+/keyRings/[^/]+/cryptoKeys/[^/]+$`)
re := regexp.MustCompile(`^projects/[^/]+/locations/[^/]+/keyRings/[^/]+/cryptoKeys/[^/]+(?:/cryptoKeyVersions/[^/]+)?$`)
matches := re.FindStringSubmatch(key.ResourceID)
if matches == nil {
return nil, fmt.Errorf("no valid resource ID found in %q", key.ResourceID)
Expand All @@ -216,8 +365,8 @@ func (key *MasterKey) newKMSClient() (*kms.KeyManagementClient, error) {
if err != nil {
return nil, err
}
if credentials != nil {
opts = append(opts, option.WithCredentialsJSON(key.credentialJSON))
if len(credentials) > 0 {
opts = append(opts, option.WithCredentialsJSON(credentials))
}
}
if key.grpcConn != nil {
Expand All @@ -244,3 +393,8 @@ func getGoogleCredentials() ([]byte, error) {
}
return []byte(defaultCredentials), nil
}

func crc32c(data []byte) uint32 {
t := crc32.MakeTable(crc32.Castagnoli)
return crc32.Checksum(data, t)
}