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// Copyright 2018 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 xchacha20poly1305
import (
"fmt"
"io"
"golang.org/x/crypto/chacha20poly1305"
"google.golang.org/protobuf/proto"
"github.com/tink-crypto/tink-go/v2/core/registry"
"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"
tpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto"
xpb "github.com/tink-crypto/tink-go/v2/proto/xchacha20_poly1305_go_proto"
)
const (
keyVersion = 0
typeURL = "type.googleapis.com/google.crypto.tink.XChaCha20Poly1305Key"
)
// keyManager generates [xpb.XChaCha20Poly1305Key] keys and produces
// instances of [subtle.XChaCha20Poly1305].
type keyManager struct{}
// Assert that keyManager implements the KeyManager interface.
var _ registry.KeyManager = (*keyManager)(nil)
// Primitive constructs a XChaCha20Poly1305 for the given serialized
// [xpb.XChaCha20Poly1305Key].
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
}
xChaCha20Poly1305Key, ok := key.(*Key)
if !ok {
return nil, fmt.Errorf("xchacha20poly1305_key_manager: invalid key type: got %T, want %T", key, (*Key)(nil))
}
ret, err := newAEAD(xChaCha20Poly1305Key)
if err != nil {
return nil, fmt.Errorf("xchacha20poly1305_key_manager: %v", err)
}
return ret, nil
}
// NewKey generates a new [xpb.XChaCha20Poly1305Key].
//
// It ignores serializedKeyFormat because the key size and other params are fixed.
func (km *keyManager) NewKey(serializedKeyFormat []byte) (proto.Message, error) {
return &xpb.XChaCha20Poly1305Key{
Version: keyVersion,
KeyValue: random.GetRandomBytes(chacha20poly1305.KeySize),
}, nil
}
// NewKeyData generates a new KeyData. It ignores serializedKeyFormat because
// the key size and other params are fixed. This should be used solely by the
// key management API.
func (km *keyManager) NewKeyData(serializedKeyFormat []byte) (*tpb.KeyData, error) {
key := &xpb.XChaCha20Poly1305Key{
Version: keyVersion,
KeyValue: random.GetRandomBytes(chacha20poly1305.KeySize),
}
serializedKey, err := proto.Marshal(key)
if err != nil {
return nil, err
}
return &tpb.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() tpb.KeyData_KeyMaterialType {
return tpb.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) {
keyFormat := new(xpb.XChaCha20Poly1305KeyFormat)
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, fmt.Errorf("xchacha20poly1305_key_manager: %v", err)
}
err := keyset.ValidateKeyVersion(keyFormat.Version, keyVersion)
if err != nil {
return nil, fmt.Errorf("xchacha20poly1305_key_manager: %v", err)
}
keyValue := make([]byte, chacha20poly1305.KeySize)
if _, err := io.ReadFull(pseudorandomness, keyValue); err != nil {
return nil, fmt.Errorf("xchacha20poly1305_key_manager: not enough pseudorandomness given")
}
return &xpb.XChaCha20Poly1305Key{
Version: keyVersion,
KeyValue: keyValue,
}, nil
}
// validateKey validates the given [xpb.XChaCha20Poly1305Key].
func (km *keyManager) validateKey(key *xpb.XChaCha20Poly1305Key) error {
err := keyset.ValidateKeyVersion(key.Version, keyVersion)
if err != nil {
return fmt.Errorf("xchacha20poly1305_key_manager: %v", err)
}
keySize := uint32(len(key.KeyValue))
if keySize != chacha20poly1305.KeySize {
return fmt.Errorf("xchacha20poly1305_key_manager: key size != %d", chacha20poly1305.KeySize)
}
return nil
}
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