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// Copyright 2022 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 jwt
import (
"fmt"
"google.golang.org/protobuf/proto"
"github.com/tink-crypto/tink-go/v2/core/registry"
"github.com/tink-crypto/tink-go/v2/keyset"
macsubtle "github.com/tink-crypto/tink-go/v2/mac/subtle"
"github.com/tink-crypto/tink-go/v2/subtle/random"
"github.com/tink-crypto/tink-go/v2/subtle"
jwtmacpb "github.com/tink-crypto/tink-go/v2/proto/jwt_hmac_go_proto"
tinkpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto"
)
const (
jwtHMACKeyVersion = 0
jwtHMACTypeURL = "type.googleapis.com/google.crypto.tink.JwtHmacKey"
)
// jwtHMACKeyManager is an implementation of the KeyManager interface
type jwtHMACKeyManager struct{}
// Assert that jwtHMACKeyManager implements the KeyManager interface.
var _ registry.KeyManager = (*jwtHMACKeyManager)(nil)
var hsAlgToHash = map[jwtmacpb.JwtHmacAlgorithm]string{
jwtmacpb.JwtHmacAlgorithm_HS256: "SHA256",
jwtmacpb.JwtHmacAlgorithm_HS384: "SHA384",
jwtmacpb.JwtHmacAlgorithm_HS512: "SHA512",
}
var hsAlgToMinKeySizeBytes = map[jwtmacpb.JwtHmacAlgorithm]int{
jwtmacpb.JwtHmacAlgorithm_HS256: 32,
jwtmacpb.JwtHmacAlgorithm_HS384: 48,
jwtmacpb.JwtHmacAlgorithm_HS512: 64,
}
func (km *jwtHMACKeyManager) Primitive(serializedKey []byte) (any, error) {
key := &jwtmacpb.JwtHmacKey{}
if err := proto.Unmarshal(serializedKey, key); err != nil {
return nil, err
}
if err := km.validateKey(key); err != nil {
return nil, err
}
hashAlg, ok := hsAlgToHash[key.GetAlgorithm()]
if !ok {
return nil, fmt.Errorf("invalid algorithm: '%v'", key.GetAlgorithm())
}
tagSize, err := subtle.GetHashDigestSize(hashAlg)
if err != nil {
return nil, err
}
mac, err := macsubtle.NewHMAC(hashAlg, key.GetKeyValue(), tagSize)
if err != nil {
return nil, err
}
var kid *string = nil
if key.GetCustomKid() != nil {
k := key.GetCustomKid().GetValue()
kid = &k
}
return newMACWithKID(mac, key.GetAlgorithm().String(), kid)
}
func (km *jwtHMACKeyManager) NewKey(serializedKeyFormat []byte) (proto.Message, error) {
if serializedKeyFormat == nil || len(serializedKeyFormat) == 0 {
return nil, fmt.Errorf("no serialized key format")
}
keyFormat := &jwtmacpb.JwtHmacKeyFormat{}
if err := proto.Unmarshal(serializedKeyFormat, keyFormat); err != nil {
return nil, err
}
if err := km.validateKeyFormat(keyFormat); err != nil {
return nil, err
}
return &jwtmacpb.JwtHmacKey{
Version: jwtHMACKeyVersion,
Algorithm: keyFormat.GetAlgorithm(),
KeyValue: random.GetRandomBytes(keyFormat.KeySize),
}, nil
}
func (km *jwtHMACKeyManager) 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: jwtHMACTypeURL,
Value: serializedKey,
KeyMaterialType: tinkpb.KeyData_SYMMETRIC,
}, nil
}
// DoesSupport indicates if this key manager supports the given key type.
func (km *jwtHMACKeyManager) DoesSupport(keyTypeURL string) bool {
return jwtHMACTypeURL == keyTypeURL
}
// TypeURL returns the key type of keys managed by this key manager.
func (km *jwtHMACKeyManager) TypeURL() string {
return jwtHMACTypeURL
}
func (km *jwtHMACKeyManager) validateKey(key *jwtmacpb.JwtHmacKey) error {
if key == nil {
return fmt.Errorf("key can't be nil")
}
if err := keyset.ValidateKeyVersion(key.Version, jwtHMACKeyVersion); err != nil {
return err
}
minKeySizeBytes, ok := hsAlgToMinKeySizeBytes[key.GetAlgorithm()]
if !ok {
return fmt.Errorf("invalid algorithm: '%v'", key.GetAlgorithm())
}
if len(key.KeyValue) < minKeySizeBytes {
return fmt.Errorf("invalid JwtHmacKey: KeyValue is too short")
}
return nil
}
func (km *jwtHMACKeyManager) validateKeyFormat(keyFormat *jwtmacpb.JwtHmacKeyFormat) error {
if keyFormat == nil {
return fmt.Errorf("key format can't be nil")
}
minKeySizeBytes, ok := hsAlgToMinKeySizeBytes[keyFormat.GetAlgorithm()]
if !ok {
return fmt.Errorf("invalid algorithm: '%v'", keyFormat.GetAlgorithm())
}
if int(keyFormat.KeySize) < minKeySizeBytes {
return fmt.Errorf("invalid JwtHmacKeyFormat: KeySize is too small")
}
return nil
}
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