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/
aes_gcm_key_manager.go
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/
aes_gcm_key_manager.go
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// Copyright 2018 Google LLC
//
// 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 aead
import (
"fmt"
"google.golang.org/protobuf/proto"
"github.com/google/tink/go/aead/subtle"
"github.com/google/tink/go/core/registry"
"github.com/google/tink/go/keyset"
"github.com/google/tink/go/subtle/random"
gcmpb "github.com/google/tink/go/proto/aes_gcm_go_proto"
tinkpb "github.com/google/tink/go/proto/tink_go_proto"
)
const (
aesGCMKeyVersion = 0
aesGCMTypeURL = "type.googleapis.com/google.crypto.tink.AesGcmKey"
)
// common errors
var errInvalidAESGCMKey = fmt.Errorf("aes_gcm_key_manager: invalid key")
var errInvalidAESGCMKeyFormat = fmt.Errorf("aes_gcm_key_manager: invalid key format")
// aesGCMKeyManager is an implementation of KeyManager interface.
// It generates new AESGCMKey keys and produces new instances of AESGCM subtle.
type aesGCMKeyManager struct{}
// Assert that aesGCMKeyManager implements the KeyManager interface.
var _ registry.KeyManager = (*aesGCMKeyManager)(nil)
// Primitive creates an AESGCM subtle for the given serialized AESGCMKey proto.
func (km *aesGCMKeyManager) Primitive(serializedKey []byte) (interface{}, error) {
if len(serializedKey) == 0 {
return nil, errInvalidAESGCMKey
}
key := new(gcmpb.AesGcmKey)
if err := proto.Unmarshal(serializedKey, key); err != nil {
return nil, errInvalidAESGCMKey
}
if err := km.validateKey(key); err != nil {
return nil, err
}
ret, err := subtle.NewAESGCM(key.KeyValue)
if err != nil {
return nil, fmt.Errorf("aes_gcm_key_manager: cannot create new primitive: %s", err)
}
return ret, nil
}
// NewKey creates a new key according to specification the given serialized AESGCMKeyFormat.
func (km *aesGCMKeyManager) NewKey(serializedKeyFormat []byte) (proto.Message, error) {
if len(serializedKeyFormat) == 0 {
return nil, errInvalidAESGCMKeyFormat
}
keyFormat := new(gcmpb.AesGcmKeyFormat)
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, errInvalidAESGCMKeyFormat
}
if err := km.validateKeyFormat(keyFormat); err != nil {
return nil, fmt.Errorf("aes_gcm_key_manager: invalid key format: %s", err)
}
keyValue := random.GetRandomBytes(keyFormat.KeySize)
return &gcmpb.AesGcmKey{
Version: aesGCMKeyVersion,
KeyValue: keyValue,
}, nil
}
// NewKeyData creates a new KeyData according to specification in the given serialized
// AESGCMKeyFormat.
// It should be used solely by the key management API.
func (km *aesGCMKeyManager) NewKeyData(serializedKeyFormat []byte) (*tinkpb.KeyData, error) {
key, err := km.NewKey(serializedKeyFormat)
if err != nil {
return nil, err
}
serializedKey, err := proto.Marshal(key)
if err != nil {
return nil, err
}
return &tinkpb.KeyData{
TypeUrl: aesGCMTypeURL,
Value: serializedKey,
KeyMaterialType: tinkpb.KeyData_SYMMETRIC,
}, nil
}
// DoesSupport indicates if this key manager supports the given key type.
func (km *aesGCMKeyManager) DoesSupport(typeURL string) bool {
return typeURL == aesGCMTypeURL
}
// TypeURL returns the key type of keys managed by this key manager.
func (km *aesGCMKeyManager) TypeURL() string {
return aesGCMTypeURL
}
// validateKey validates the given AESGCMKey.
func (km *aesGCMKeyManager) validateKey(key *gcmpb.AesGcmKey) error {
err := keyset.ValidateKeyVersion(key.Version, aesGCMKeyVersion)
if err != nil {
return fmt.Errorf("aes_gcm_key_manager: %s", err)
}
keySize := uint32(len(key.KeyValue))
if err := subtle.ValidateAESKeySize(keySize); err != nil {
return fmt.Errorf("aes_gcm_key_manager: %s", err)
}
return nil
}
// validateKeyFormat validates the given AESGCMKeyFormat.
func (km *aesGCMKeyManager) validateKeyFormat(format *gcmpb.AesGcmKeyFormat) error {
if err := subtle.ValidateAESKeySize(format.KeySize); err != nil {
return fmt.Errorf("aes_gcm_key_manager: %s", err)
}
return nil
}