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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 streamingaead
import (
"errors"
"fmt"
"io"
"google.golang.org/protobuf/proto"
subtleaead "github.com/tink-crypto/tink-go/v2/aead/subtle"
"github.com/tink-crypto/tink-go/v2/keyset"
"github.com/tink-crypto/tink-go/v2/streamingaead/subtle"
"github.com/tink-crypto/tink-go/v2/subtle/random"
ghpb "github.com/tink-crypto/tink-go/v2/proto/aes_gcm_hkdf_streaming_go_proto"
commonpb "github.com/tink-crypto/tink-go/v2/proto/common_go_proto"
tinkpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto"
)
const (
aesGCMHKDFKeyVersion = 0
aesGCMHKDFTypeURL = "type.googleapis.com/google.crypto.tink.AesGcmHkdfStreamingKey"
)
var (
errInvalidAESGCMHKDFKey = errors.New("aes_gcm_hkdf_key_manager: invalid key")
errInvalidAESGCMHKDFKeyFormat = errors.New("aes_gcm_hkdf_key_manager: invalid key format")
)
// aesGCMHKDFKeyManager is an implementation of KeyManager interface.
// It generates new AESGCMHKDFKey keys and produces new instances of AESGCMHKDF subtle.
type aesGCMHKDFKeyManager struct{}
// Primitive creates an AESGCMHKDF subtle for the given serialized AESGCMHKDFKey proto.
func (km *aesGCMHKDFKeyManager) Primitive(serializedKey []byte) (any, error) {
if len(serializedKey) == 0 {
return nil, errInvalidAESGCMHKDFKey
}
key := &ghpb.AesGcmHkdfStreamingKey{}
if err := proto.Unmarshal(serializedKey, key); err != nil {
return nil, errInvalidAESGCMHKDFKey
}
if err := km.validateKey(key); err != nil {
return nil, err
}
ret, err := subtle.NewAESGCMHKDF(
key.GetKeyValue(),
key.GetParams().GetHkdfHashType().String(),
int(key.GetParams().GetDerivedKeySize()),
int(key.GetParams().GetCiphertextSegmentSize()),
// no first segment offset
0)
if err != nil {
return nil, fmt.Errorf("aes_gcm_hkdf_key_manager: cannot create new primitive: %s", err)
}
return ret, nil
}
// NewKey creates a new key according to specification in the given serialized
// AesGcmHkdfStreamingKeyFormat.
func (km *aesGCMHKDFKeyManager) NewKey(serializedKeyFormat []byte) (proto.Message, error) {
if len(serializedKeyFormat) == 0 {
return nil, errInvalidAESGCMHKDFKeyFormat
}
keyFormat := &ghpb.AesGcmHkdfStreamingKeyFormat{}
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, errInvalidAESGCMHKDFKeyFormat
}
if err := km.validateKeyFormat(keyFormat); err != nil {
return nil, fmt.Errorf("aes_gcm_hkdf_key_manager: invalid key format: %s", err)
}
return &ghpb.AesGcmHkdfStreamingKey{
Version: aesGCMHKDFKeyVersion,
KeyValue: random.GetRandomBytes(keyFormat.GetKeySize()),
Params: keyFormat.Params,
}, nil
}
// NewKeyData creates a new KeyData according to specification in the given serialized AesGcmHkdfStreamingKeyFormat.
// It should be used solely by the key management API.
func (km *aesGCMHKDFKeyManager) 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: km.TypeURL(),
Value: serializedKey,
KeyMaterialType: km.KeyMaterialType(),
}, nil
}
// DoesSupport indicates if this key manager supports the given key type.
func (km *aesGCMHKDFKeyManager) DoesSupport(typeURL string) bool {
return typeURL == aesGCMHKDFTypeURL
}
// TypeURL returns the key type of keys managed by this key manager.
func (km *aesGCMHKDFKeyManager) TypeURL() string {
return aesGCMHKDFTypeURL
}
// KeyMaterialType returns the key material type of this key manager.
func (km *aesGCMHKDFKeyManager) KeyMaterialType() tinkpb.KeyData_KeyMaterialType {
return tinkpb.KeyData_SYMMETRIC
}
// DeriveKey derives a new key from serializedKeyFormat and pseudorandomness.
func (km *aesGCMHKDFKeyManager) DeriveKey(serializedKeyFormat []byte, pseudorandomness io.Reader) (proto.Message, error) {
if len(serializedKeyFormat) == 0 {
return nil, errInvalidAESGCMHKDFKeyFormat
}
keyFormat := &ghpb.AesGcmHkdfStreamingKeyFormat{}
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, errInvalidAESGCMHKDFKeyFormat
}
if err := km.validateKeyFormat(keyFormat); err != nil {
return nil, fmt.Errorf("aes_gcm_hkdf_key_manager: invalid key format: %v", err)
}
if err := keyset.ValidateKeyVersion(keyFormat.GetVersion(), aesGCMHKDFKeyVersion); err != nil {
return nil, fmt.Errorf("aes_gcm_hkdf_key_manager: invalid key version: %s", err)
}
keyValue := make([]byte, keyFormat.GetKeySize())
if _, err := io.ReadFull(pseudorandomness, keyValue); err != nil {
return nil, fmt.Errorf("aes_gcm_hkdf_key_manager: not enough pseudorandomness given")
}
return &ghpb.AesGcmHkdfStreamingKey{
Version: aesGCMHKDFKeyVersion,
KeyValue: keyValue,
Params: keyFormat.GetParams(),
}, nil
}
// validateKey validates the given AESGCMHKDFKey.
func (km *aesGCMHKDFKeyManager) validateKey(key *ghpb.AesGcmHkdfStreamingKey) error {
if err := keyset.ValidateKeyVersion(key.Version, aesGCMHKDFKeyVersion); err != nil {
return fmt.Errorf("aes_gcm_hkdf_key_manager: %s", err)
}
keySize := uint32(len(key.GetKeyValue()))
if err := subtleaead.ValidateAESKeySize(keySize); err != nil {
return fmt.Errorf("aes_gcm_hkdf_key_manager: %s", err)
}
if err := km.validateParams(key.GetParams()); err != nil {
return fmt.Errorf("aes_gcm_hkdf_key_manager: %s", err)
}
return nil
}
// validateKeyFormat validates the given AESGCMHKDFKeyFormat.
func (km *aesGCMHKDFKeyManager) validateKeyFormat(format *ghpb.AesGcmHkdfStreamingKeyFormat) error {
if err := subtleaead.ValidateAESKeySize(format.KeySize); err != nil {
return fmt.Errorf("aes_gcm_hkdf_key_manager: %s", err)
}
if err := km.validateParams(format.GetParams()); err != nil {
return fmt.Errorf("aes_gcm_hkdf_key_manager: %s", err)
}
return nil
}
// validateKeyFormat validates the given AESGCMHKDFKeyFormat.
func (km *aesGCMHKDFKeyManager) validateParams(params *ghpb.AesGcmHkdfStreamingParams) error {
if err := subtleaead.ValidateAESKeySize(params.GetDerivedKeySize()); err != nil {
return fmt.Errorf("aes_gcm_hkdf_key_manager: %s", err)
}
if params.GetHkdfHashType() != commonpb.HashType_SHA1 && params.GetHkdfHashType() != commonpb.HashType_SHA256 && params.GetHkdfHashType() != commonpb.HashType_SHA512 {
return errors.New("unknown HKDF hash type")
}
if params.GetCiphertextSegmentSize() > 0x7fffffff {
return errors.New("CiphertextSegmentSize must be at most 2^31 - 1")
}
minSegmentSize := params.GetDerivedKeySize() + subtle.AESGCMHKDFNoncePrefixSizeInBytes + subtle.AESGCMHKDFTagSizeInBytes + 2
if params.GetCiphertextSegmentSize() < minSegmentSize {
return fmt.Errorf("ciphertext segment_size must be at least (derivedKeySize + noncePrefixInBytes + tagSizeInBytes + 2)")
}
return nil
}
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