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// Copyright 2021 Northern.tech AS
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package gcp
import (
"context"
"encoding/asn1"
"encoding/base64"
"hash/crc32"
"math/big"
"time"
"github.com/mendersoftware/mender-artifact/artifact"
kms "cloud.google.com/go/kms/apiv1"
gax "github.com/googleapis/gax-go/v2"
"github.com/minio/sha256-simd"
"github.com/pkg/errors"
kmspb "google.golang.org/genproto/googleapis/cloud/kms/v1"
//"google.golang.org/protobuf/types/known/wrapperspb"
)
// NewKMSSigner creates a Signer that signs using a key from
// Google Cloud's Key Management Service.
// Release resources by calling Close().
func NewKMSSigner(ctx context.Context, name string) (*KMS, error) {
client, err := kms.NewKeyManagementClient(ctx)
if err != nil {
return nil, errors.Wrap(err, "signer: error connecting to KMS")
}
return &KMS{
name: name,
client: client,
rpcTimeout: 60 * time.Second,
}, nil
}
type KMS struct {
name string
client googleKMSClient
rpcTimeout time.Duration
}
func (k *KMS) Sign(message []byte) ([]byte, error) {
ctx, cancel := context.WithTimeout(context.TODO(), k.rpcTimeout)
defer cancel()
// Although we don't need this verify method, we use this to
// check that the key fits our supported algorithms. When
// performing the actual signature, there's no way to actually
// check the key's algorithm.
sm, err := k.getKMSKeyAndVerifyMethod(ctx)
if err != nil {
return nil, err
}
h := sha256.Sum256(message)
//digestCRC32C := checksum(h[:])
result, err := k.client.AsymmetricSign(ctx, &kmspb.AsymmetricSignRequest{
Name: k.name,
Digest: &kmspb.Digest{
Digest: &kmspb.Digest_Sha256{
Sha256: h[:],
},
},
//DigestCrc32C: wrapperspb.Int64(digestCRC32C),
})
if err != nil {
return nil, errors.Wrap(err, "signer: error signing image with KMS")
}
/*
if !result.VerifiedDigestCrc32C {
return nil, errors.New("signer: KMS signing request corrupted")
}
if checksum(result.Signature) != result.SignatureCrc32C.Value {
return nil, errors.New("signer: KMS signing response corrupted")
}
*/
switch sm.Method.(type) {
case *artifact.RSA:
sigBase64 := make([]byte, base64.StdEncoding.EncodedLen(len(result.Signature)))
base64.StdEncoding.Encode(sigBase64, result.Signature)
return sigBase64, nil
case *artifact.ECDSA256:
// KMS serializes ECDSA keys in ASN1 format. Convert it back into our own format.
var parsedSig struct{ R, S *big.Int }
if _, err := asn1.Unmarshal(result.Signature, &parsedSig); err != nil {
return nil, errors.Wrap(err, "signer: failed to parse ECDSA signature")
}
marshaledSigBytes, err := artifact.MarshalECDSASignature(parsedSig.R, parsedSig.S)
if err != nil {
return nil, err
}
outputSig := make([]byte, base64.StdEncoding.EncodedLen(len(marshaledSigBytes)))
base64.StdEncoding.Encode(outputSig, marshaledSigBytes)
return outputSig, nil
default:
return nil, errors.New("signer: unsupported algorithm")
}
}
func (k *KMS) Verify(message, sig []byte) error {
ctx, cancel := context.WithTimeout(context.TODO(), k.rpcTimeout)
defer cancel()
sm, err := k.getKMSKeyAndVerifyMethod(ctx)
if err != nil {
return err
}
dec := make([]byte, base64.StdEncoding.DecodedLen(len(sig)))
decLen, err := base64.StdEncoding.Decode(dec, sig)
if err != nil {
return errors.Wrap(err, "signer: error decoding signature")
}
return sm.Method.Verify(message, dec[:decLen], sm.Key)
}
func (k *KMS) getKMSKeyAndVerifyMethod(ctx context.Context) (*artifact.SigningMethod, error) {
response, err := k.client.GetPublicKey(ctx, &kmspb.GetPublicKeyRequest{Name: k.name})
if err != nil {
return nil, errors.Wrap(err, "signer: error getting public key from KMS")
}
/*
if checksum([]byte(response.Pem)) != response.PemCrc32C.Value {
return nil, errors.New("signer: KMS verification response corrupted")
}
*/
return artifact.GetKeyAndVerifyMethod([]byte(response.Pem))
}
func (k *KMS) Close() error {
return k.client.Close()
}
func checksum(data []byte) int64 {
crcTable := crc32.MakeTable(crc32.Castagnoli)
return int64(crc32.Checksum(data, crcTable))
}
type googleKMSClient interface {
AsymmetricSign(context.Context, *kmspb.AsymmetricSignRequest,
...gax.CallOption) (*kmspb.AsymmetricSignResponse, error)
GetPublicKey(context.Context, *kmspb.GetPublicKeyRequest,
...gax.CallOption) (*kmspb.PublicKey, error)
Close() error
}
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