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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"
"google.golang.org/protobuf/proto"
subtleaead "github.com/tink-crypto/tink-go/v2/aead/subtle"
"github.com/tink-crypto/tink-go/v2/keyset"
subtlemac "github.com/tink-crypto/tink-go/v2/mac/subtle"
"github.com/tink-crypto/tink-go/v2/streamingaead/subtle"
"github.com/tink-crypto/tink-go/v2/subtle/random"
chpb "github.com/tink-crypto/tink-go/v2/proto/aes_ctr_hmac_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 (
aesCTRHMACKeyVersion = 0
aesCTRHMACTypeURL = "type.googleapis.com/google.crypto.tink.AesCtrHmacStreamingKey"
)
var (
errInvalidAESCTRHMACKey = errors.New("aes_ctr_hmac_key_manager: invalid key")
errInvalidAESCTRHMACKeyFormat = errors.New("aes_ctr_hmac_key_manager: invalid key format")
)
// aesCTRHMACKeyManager is an implementation of KeyManager interface.
//
// It generates new AESCTRHMACKey keys and produces new instances of AESCTRHMAC
// subtle.
type aesCTRHMACKeyManager struct{}
// Primitive creates an AESCTRHMAC subtle for the given serialized
// AESCTRHMACKey proto.
func (km *aesCTRHMACKeyManager) Primitive(serializedKey []byte) (any, error) {
if len(serializedKey) == 0 {
return nil, errInvalidAESCTRHMACKey
}
key := &chpb.AesCtrHmacStreamingKey{}
if err := proto.Unmarshal(serializedKey, key); err != nil {
return nil, errInvalidAESCTRHMACKey
}
if err := km.validateKey(key); err != nil {
return nil, err
}
p, err := subtle.NewAESCTRHMAC(
key.GetKeyValue(),
key.GetParams().GetHkdfHashType().String(),
int(key.GetParams().GetDerivedKeySize()),
key.GetParams().GetHmacParams().GetHash().String(),
int(key.GetParams().GetHmacParams().GetTagSize()),
int(key.GetParams().GetCiphertextSegmentSize()),
// No first segment offset.
0)
if err != nil {
return nil, fmt.Errorf("aes_ctr_hmac_key_manager: cannot create new primitive: %s", err)
}
return p, nil
}
// NewKey creates a new key according to specification in the given serialized
// AesCtrHmacStreamingKeyFormat.
func (km *aesCTRHMACKeyManager) NewKey(serializedKeyFormat []byte) (proto.Message, error) {
if len(serializedKeyFormat) == 0 {
return nil, errInvalidAESCTRHMACKeyFormat
}
keyFormat := &chpb.AesCtrHmacStreamingKeyFormat{}
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, errInvalidAESCTRHMACKeyFormat
}
if err := km.validateKeyFormat(keyFormat); err != nil {
return nil, fmt.Errorf("%s: %s", errInvalidAESCTRHMACKeyFormat, err)
}
return &chpb.AesCtrHmacStreamingKey{
Version: aesCTRHMACKeyVersion,
KeyValue: random.GetRandomBytes(keyFormat.GetKeySize()),
Params: keyFormat.Params,
}, nil
}
// NewKeyData creates a new KeyData according to specification in the given
// serialized AesCtrHmacStreamingKeyFormat.
//
// It should be used solely by the key management API.
func (km *aesCTRHMACKeyManager) 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: tinkpb.KeyData_SYMMETRIC,
}, nil
}
// DoesSupport indicates if this key manager supports the given key type.
func (km *aesCTRHMACKeyManager) DoesSupport(typeURL string) bool {
return typeURL == aesCTRHMACTypeURL
}
// TypeURL returns the key type of keys managed by this key manager.
func (km *aesCTRHMACKeyManager) TypeURL() string {
return aesCTRHMACTypeURL
}
// validateKey validates the given AESCTRHMACKey.
func (km *aesCTRHMACKeyManager) validateKey(key *chpb.AesCtrHmacStreamingKey) error {
if err := keyset.ValidateKeyVersion(key.GetVersion(), aesCTRHMACKeyVersion); err != nil {
return err
}
keySize := uint32(len(key.GetKeyValue()))
if err := subtleaead.ValidateAESKeySize(keySize); err != nil {
return err
}
if err := km.validateParams(key.GetParams()); err != nil {
return err
}
return nil
}
// validateKeyFormat validates the given AESCTRHMACKeyFormat.
func (km *aesCTRHMACKeyManager) validateKeyFormat(format *chpb.AesCtrHmacStreamingKeyFormat) error {
if err := subtleaead.ValidateAESKeySize(format.KeySize); err != nil {
return err
}
if err := km.validateParams(format.GetParams()); err != nil {
return err
}
return nil
}
// validateParams validates the given AESCTRHMACStreamingParams.
func (km *aesCTRHMACKeyManager) validateParams(params *chpb.AesCtrHmacStreamingParams) error {
if err := subtleaead.ValidateAESKeySize(params.GetDerivedKeySize()); err != nil {
return err
}
if params.GetHkdfHashType() != commonpb.HashType_SHA1 && params.GetHkdfHashType() != commonpb.HashType_SHA256 && params.GetHkdfHashType() != commonpb.HashType_SHA512 {
return fmt.Errorf("Invalid HKDF hash type (%s)", params.GetHkdfHashType())
}
if params.GetHmacParams().GetHash() != commonpb.HashType_SHA1 && params.GetHmacParams().GetHash() != commonpb.HashType_SHA256 && params.GetHmacParams().GetHash() != commonpb.HashType_SHA512 {
return fmt.Errorf("Invalid tag algorithm (%s)", params.GetHmacParams().GetHash())
}
hmacHash := commonpb.HashType_name[int32(params.GetHmacParams().GetHash())]
if err := subtlemac.ValidateHMACParams(hmacHash, subtle.AESCTRHMACKeySizeInBytes, params.GetHmacParams().GetTagSize()); err != nil {
return err
}
minSegmentSize := params.GetDerivedKeySize() + subtle.AESCTRHMACNoncePrefixSizeInBytes + params.GetHmacParams().GetTagSize() + 2
if params.GetCiphertextSegmentSize() < minSegmentSize {
return fmt.Errorf("ciphertext segment size must be at least (derivedKeySize + noncePrefixInBytes + tagSizeInBytes + 2)")
}
if params.GetCiphertextSegmentSize() > 0x7fffffff {
return fmt.Errorf("ciphertext segment size must be at most 2^31 - 1")
}
return nil
}
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