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// Copyright 2024 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 xaesgcm
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/internalapi"
"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"
tinkpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto"
xaesgcmpb "github.com/tink-crypto/tink-go/v2/proto/x_aes_gcm_go_proto"
)
const (
keyVersion = 0
typeURL = "type.googleapis.com/google.crypto.tink.XAesGcmKey"
)
// keyManager generates [xaesgcmpb.XAesGcmKey] keys and produces
// instances of [tink.AEAD] that implement X-AES-GCM.
type keyManager struct{}
// Assert that keyManager implements the KeyManager interface.
var _ registry.KeyManager = (*keyManager)(nil)
// Primitive constructs a [tink.AEAD] for the given serialized
// [xaesgcmpb.XAesGcmKey].
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
}
xAESGCMKey, ok := key.(*Key)
if !ok {
return nil, fmt.Errorf("xaesgcm_key_manager: invalid key type: got %T, want %T", key, (*Key)(nil))
}
ret, err := NewAEAD(xAESGCMKey, internalapi.Token{})
if err != nil {
return nil, fmt.Errorf("xaesgcm_key_manager: %v", err)
}
return ret, nil
}
// NewKey generates a new [xaesgcmpb.XAesGcmKey].
func (km *keyManager) NewKey(serializedKeyFormat []byte) (proto.Message, error) {
if len(serializedKeyFormat) == 0 {
return nil, fmt.Errorf("xaesgcm_key_manager: empty key format")
}
keyFormat := new(xaesgcmpb.XAesGcmKeyFormat)
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, fmt.Errorf("xaesgcm_key_manager: %v", err)
}
if err := validateKeyFormat(keyFormat); err != nil {
return nil, fmt.Errorf("xaesgcm_key_manager: %v", err)
}
return &xaesgcmpb.XAesGcmKey{
Version: keyVersion,
KeyValue: random.GetRandomBytes(32),
Params: &xaesgcmpb.XAesGcmParams{
SaltSize: keyFormat.GetParams().GetSaltSize(),
},
}, nil
}
// NewKeyData generates a new KeyData. This should be used solely by the
// key management API.
func (km *keyManager) NewKeyData(serializedKeyFormat []byte) (*tinkpb.KeyData, error) {
if len(serializedKeyFormat) == 0 {
return nil, fmt.Errorf("xaesgcm_key_manager: empty key format")
}
keyFormat := new(xaesgcmpb.XAesGcmKeyFormat)
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, fmt.Errorf("xaesgcm_key_manager: %v", err)
}
if err := validateKeyFormat(keyFormat); err != nil {
return nil, fmt.Errorf("xaesgcm_key_manager: %v", err)
}
key := &xaesgcmpb.XAesGcmKey{
Version: keyVersion,
KeyValue: random.GetRandomBytes(32),
Params: &xaesgcmpb.XAesGcmParams{
SaltSize: keyFormat.GetParams().GetSaltSize(),
},
}
serializedKey, err := proto.Marshal(key)
if err != nil {
return nil, fmt.Errorf("xaesgcm_key_manager: %v", err)
}
return &tinkpb.KeyData{
TypeUrl: typeURL,
Value: serializedKey,
KeyMaterialType: km.KeyMaterialType(),
}, nil
}
// DoesSupport checks whether this key manager supports the given key type.
func (km *keyManager) DoesSupport(typeURL string) bool { return km.TypeURL() == typeURL }
// TypeURL returns the type URL of keys managed by this key manager.
func (km *keyManager) TypeURL() string { return typeURL }
// KeyMaterialType returns the key material type of this key manager.
func (km *keyManager) KeyMaterialType() tinkpb.KeyData_KeyMaterialType {
return tinkpb.KeyData_SYMMETRIC
}
// DeriveKey derives a new key from serializedKeyFormat and pseudorandomness.
//
// Unlike NewKey, DeriveKey validates serializedKeyFormat's version.
func (km *keyManager) DeriveKey(serializedKeyFormat []byte, pseudorandomness io.Reader) (proto.Message, error) {
if len(serializedKeyFormat) == 0 {
return nil, fmt.Errorf("xaesgcm_key_manager: empty key format")
}
keyFormat := new(xaesgcmpb.XAesGcmKeyFormat)
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, fmt.Errorf("xaesgcm_key_manager: %v", err)
}
err := keyset.ValidateKeyVersion(keyFormat.Version, keyVersion)
if err != nil {
return nil, fmt.Errorf("xaesgcm_key_manager: %v", err)
}
keyValue := make([]byte, 32)
if _, err := io.ReadFull(pseudorandomness, keyValue); err != nil {
return nil, fmt.Errorf("xaesgcm_key_manager: not enough pseudorandomness given")
}
return &xaesgcmpb.XAesGcmKey{
Version: keyVersion,
KeyValue: keyValue,
Params: &xaesgcmpb.XAesGcmParams{
SaltSize: keyFormat.GetParams().GetSaltSize(),
},
}, nil
}
func validateKeyFormat(format *xaesgcmpb.XAesGcmKeyFormat) error {
if err := keyset.ValidateKeyVersion(format.Version, keyVersion); err != nil {
return fmt.Errorf("xaesgcm_key_manager: %v", err)
}
saltSize := format.GetParams().GetSaltSize()
if saltSize < 8 || saltSize > 12 {
return fmt.Errorf("xaesgcm_key_manager: salt size = %d, want in [8, 12]", saltSize)
}
return nil
}
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