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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 aesgcm
import (
"fmt"
"io"
"google.golang.org/protobuf/proto"
"github.com/tink-crypto/tink-go/v2/core/registry"
"github.com/tink-crypto/tink-go/v2/internal/aead"
"github.com/tink-crypto/tink-go/v2/internal/protoserialization"
"github.com/tink-crypto/tink-go/v2/keyset"
"github.com/tink-crypto/tink-go/v2/subtle/random"
gcmpb "github.com/tink-crypto/tink-go/v2/proto/aes_gcm_go_proto"
tinkpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto"
)
const (
keyVersion = 0
typeURL = "type.googleapis.com/google.crypto.tink.AesGcmKey"
)
// common errors
var errInvalidKey = fmt.Errorf("aes_gcm_key_manager: invalid key")
var errInvalidKeyFormat = fmt.Errorf("aes_gcm_key_manager: invalid key format")
// keyManager is an implementation of KeyManager interface.
// It generates new AESGCMKey keys and produces new instances of AESGCM subtle.
type keyManager struct{}
// Assert that keyManager implements the KeyManager interface.
var _ registry.KeyManager = (*keyManager)(nil)
// Primitive creates an AESGCM subtle for the given serialized AESGCMKey proto.
func (km *keyManager) Primitive(serializedKey []byte) (any, error) {
keySerialization, err := protoserialization.NewKeySerialization(&tinkpb.KeyData{
TypeUrl: typeURL,
Value: serializedKey,
KeyMaterialType: tinkpb.KeyData_SYMMETRIC,
}, tinkpb.OutputPrefixType_RAW, 0)
if err != nil {
return nil, err
}
key, err := protoserialization.ParseKey(keySerialization)
if err != nil {
return nil, err
}
aesGCMKey, ok := key.(*Key)
if !ok {
return nil, fmt.Errorf("aesgcm_key_manager: invalid key type: got %T, want %T", key, (*Key)(nil))
}
ret, err := NewAEAD(aesGCMKey)
if err != nil {
return nil, fmt.Errorf("aesgcm_key_manager: %v", err)
}
return ret, nil
}
// NewKey creates a new key according to specification the given serialized AESGCMKeyFormat.
func (km *keyManager) NewKey(serializedKeyFormat []byte) (proto.Message, error) {
if len(serializedKeyFormat) == 0 {
return nil, errInvalidKeyFormat
}
keyFormat := new(gcmpb.AesGcmKeyFormat)
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, errInvalidKeyFormat
}
if err := km.validateKeyFormat(keyFormat); err != nil {
return nil, fmt.Errorf("aes_gcm_key_manager: invalid key format: %s", err)
}
keyBytes := random.GetRandomBytes(keyFormat.KeySize)
return &gcmpb.AesGcmKey{
Version: keyVersion,
KeyValue: keyBytes,
}, 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 *keyManager) 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: typeURL,
Value: serializedKey,
KeyMaterialType: km.KeyMaterialType(),
}, nil
}
// DoesSupport indicates if this key manager supports the given key type.
func (km *keyManager) DoesSupport(typeURL string) bool { return typeURL == km.TypeURL() }
// TypeURL returns the key type of keys managed by this key manager.
func (km *keyManager) TypeURL() string { return typeURL }
// KeyMaterialType returns the key material type of the key manager.
func (km *keyManager) KeyMaterialType() tinkpb.KeyData_KeyMaterialType {
return tinkpb.KeyData_SYMMETRIC
}
// DeriveKey derives a new key from serializedKeyFormat and pseudorandomness.
func (km *keyManager) DeriveKey(serializedKeyFormat []byte, pseudorandomness io.Reader) (proto.Message, error) {
if len(serializedKeyFormat) == 0 {
return nil, errInvalidKeyFormat
}
keyFormat := new(gcmpb.AesGcmKeyFormat)
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, errInvalidKeyFormat
}
if err := km.validateKeyFormat(keyFormat); err != nil {
return nil, fmt.Errorf("aes_gcm_key_manager: invalid key format: %s", err)
}
if err := keyset.ValidateKeyVersion(keyFormat.GetVersion(), keyVersion); err != nil {
return nil, fmt.Errorf("aes_gcm_key_manager: invalid key version: %s", err)
}
keyBytes := make([]byte, keyFormat.GetKeySize())
if _, err := io.ReadFull(pseudorandomness, keyBytes); err != nil {
return nil, fmt.Errorf("aes_gcm_key_manager: not enough pseudorandomness given")
}
return &gcmpb.AesGcmKey{
Version: keyVersion,
KeyValue: keyBytes,
}, nil
}
// validateKey validates the given AESGCMKey.
func (km *keyManager) validateKey(key *gcmpb.AesGcmKey) error {
if err := keyset.ValidateKeyVersion(key.Version, keyVersion); err != nil {
return fmt.Errorf("aes_gcm_key_manager: %s", err)
}
keySize := uint32(len(key.GetKeyValue()))
if err := aead.ValidateAESKeySize(keySize); err != nil {
return fmt.Errorf("aes_gcm_key_manager: %s", err)
}
return nil
}
// validateKeyFormat validates the given AESGCMKeyFormat.
func (km *keyManager) validateKeyFormat(format *gcmpb.AesGcmKeyFormat) error {
if err := aead.ValidateAESKeySize(format.KeySize); err != nil {
return fmt.Errorf("aes_gcm_key_manager: %s", err)
}
return nil
}
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