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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/core/registry"
"github.com/tink-crypto/tink-go/v2/keyset"
"github.com/tink-crypto/tink-go/v2/prf/subtle"
"github.com/tink-crypto/tink-go/v2/subtle/random"
cmacpb "github.com/tink-crypto/tink-go/v2/proto/aes_cmac_prf_go_proto"
tinkpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto"
)
const (
keyVersion = 0
typeURL = "type.googleapis.com/google.crypto.tink.AesCmacPrfKey"
)
// keyManager implements the [registry.KeyManager] interface. It generates
// new AES-CMAC keys and produces new instances of [prf.PRF].
type keyManager struct{}
var _ registry.KeyManager = (*keyManager)(nil)
// Primitive constructs a AES-CMAC [prf.PRF] instance for the given
// serialized [cmacpb.AesCmacPrfKey].
func (km *keyManager) Primitive(serializedKey []byte) (any, error) {
if len(serializedKey) == 0 {
return nil, fmt.Errorf("aes_cmac_prf_key_manager: empty key")
}
key := new(cmacpb.AesCmacPrfKey)
if err := proto.Unmarshal(serializedKey, key); err != nil {
return nil, fmt.Errorf("aes_cmac_prf_key_manager: %v", err)
}
if err := km.validateKey(key); err != nil {
return nil, fmt.Errorf("aes_cmac_prf_key_manager: %v", err)
}
return subtle.NewAESCMACPRF(key.KeyValue)
}
// NewKey generates a new [cmacpb.AesCmacPrfKey] according to specification
// in the given [cmacpb.AesCmacPrfKeyFormat].
func (km *keyManager) NewKey(serializedKeyFormat []byte) (proto.Message, error) {
if len(serializedKeyFormat) == 0 {
return nil, fmt.Errorf("aes_cmac_prf_key_manager: empty key")
}
keyFormat := new(cmacpb.AesCmacPrfKeyFormat)
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, fmt.Errorf("aes_cmac_prf_key_manager: %v", err)
}
if err := km.validateKeyFormat(keyFormat); err != nil {
return nil, fmt.Errorf("aes_cmac_prf_key_manager: invalid key format: %s", err)
}
keyValue := random.GetRandomBytes(keyFormat.KeySize)
return &cmacpb.AesCmacPrfKey{
Version: keyVersion,
KeyValue: keyValue,
}, nil
}
// NewKeyData generates a new [tinkpb.KeyData] according to specification in
// the given serialized [cmacpb.AesCmacPrfKeyFormat]. 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, fmt.Errorf("aes_cmac_prf_key_manager: %v", err)
}
serializedKey, err := proto.Marshal(key)
if err != nil {
return nil, fmt.Errorf("aes_cmac_prf_key_manager: %v", err)
}
return &tinkpb.KeyData{
TypeUrl: typeURL,
Value: serializedKey,
KeyMaterialType: tinkpb.KeyData_SYMMETRIC,
}, nil
}
// DoesSupport checks whether this key manager 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 key manager.
func (km *keyManager) TypeURL() string { return typeURL }
// validateKey validates the given [cmacpb.AesCmacPrfKey]. It only validates the
// version of the key because other parameters will be validated in
// primitive construction.
func (km *keyManager) validateKey(key *cmacpb.AesCmacPrfKey) error {
err := keyset.ValidateKeyVersion(key.Version, keyVersion)
if err != nil {
return fmt.Errorf("aes_cmac_prf_key_manager: invalid version: %s", err)
}
keySize := uint32(len(key.KeyValue))
return subtle.ValidateAESCMACPRFParams(keySize)
}
// validateKeyFormat validates the given HMACKeyFormat
func (km *keyManager) validateKeyFormat(format *cmacpb.AesCmacPrfKeyFormat) error {
return subtle.ValidateAESCMACPRFParams(format.KeySize)
}
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