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// Copyright 2020 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 aescmac
import (
"fmt"
"google.golang.org/protobuf/proto"
"github.com/tink-crypto/tink-go/v2/keyset"
"github.com/tink-crypto/tink-go/v2/mac/subtle"
"github.com/tink-crypto/tink-go/v2/subtle/random"
cmacpb "github.com/tink-crypto/tink-go/v2/proto/aes_cmac_go_proto"
tinkpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto"
)
const (
keyVersion = 0
typeURL = "type.googleapis.com/google.crypto.tink.AesCmacKey"
)
// keyManager generates new AES-CMAC keys and produces new instances of AES-CMAC.
type keyManager struct{}
// Primitive constructs a AES-CMAC instance for the given serialized CMACKey.
func (km *keyManager) Primitive(serializedKey []byte) (any, error) {
if len(serializedKey) == 0 {
return nil, fmt.Errorf("aes_cmac_key_manager: empty serialized key")
}
key := new(cmacpb.AesCmacKey)
if err := proto.Unmarshal(serializedKey, key); err != nil {
return nil, fmt.Errorf("aes_cmac_key_manager: %v", err)
}
if err := km.validateKey(key); err != nil {
return nil, err
}
cmac, err := subtle.NewAESCMAC(key.KeyValue, key.GetParams().GetTagSize())
if err != nil {
return nil, err
}
return cmac, nil
}
// NewKey generates a new AesCmacKey according to specification in the given AesCmacKeyFormat.
func (km *keyManager) NewKey(serializedKeyFormat []byte) (proto.Message, error) {
if len(serializedKeyFormat) == 0 {
return nil, fmt.Errorf("aes_cmac_key_manager: empty key format")
}
keyFormat := new(cmacpb.AesCmacKeyFormat)
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, fmt.Errorf("aes_cmac_key_manager: %v", err)
}
if err := km.validateKeyFormat(keyFormat); err != nil {
return nil, fmt.Errorf("aes_cmac_key_manager: invalid key format: %s", err)
}
keyValue := random.GetRandomBytes(keyFormat.KeySize)
return &cmacpb.AesCmacKey{
Version: keyVersion,
Params: keyFormat.Params,
KeyValue: keyValue,
}, nil
}
// NewKeyData generates a new KeyData according to specification in the given
// serialized AesCmacKeyFormat. This 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, fmt.Errorf("aes_cmac_key_manager: %v", err)
}
return &tinkpb.KeyData{
TypeUrl: typeURL,
Value: serializedKey,
KeyMaterialType: tinkpb.KeyData_SYMMETRIC,
}, nil
}
// DoesSupport checks whether this KeyManager supports the given key type.
func (km *keyManager) DoesSupport(typeURL string) bool { return typeURL == km.TypeURL() }
// TypeURL returns the type URL of keys managed by this KeyManager.
func (km *keyManager) TypeURL() string { return typeURL }
// validateKey validates the given AesCmacKey. It only validates the version of the
// key because other parameters will be validated in primitive construction.
func (km *keyManager) validateKey(key *cmacpb.AesCmacKey) error {
err := keyset.ValidateKeyVersion(key.Version, keyVersion)
if err != nil {
return fmt.Errorf("aes_cmac_key_manager: invalid version: %s", err)
}
keySize := uint32(len(key.KeyValue))
return subtle.ValidateCMACParams(keySize, key.GetParams().GetTagSize())
}
// validateKeyFormat validates the given AesCmacKeyFormat
func (km *keyManager) validateKeyFormat(format *cmacpb.AesCmacKeyFormat) error {
return subtle.ValidateCMACParams(format.KeySize, format.GetParams().GetTagSize())
}
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