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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 hybrid provides HybridEncrypt/Decrypt primitive-specific test
// utilities.
package hybrid
import (
"errors"
"fmt"
"google.golang.org/protobuf/proto"
"github.com/tink-crypto/tink-go/v2/keyset"
"github.com/tink-crypto/tink-go/v2/testkeyset"
hpkepb "github.com/tink-crypto/tink-go/v2/proto/hpke_go_proto"
tinkpb "github.com/tink-crypto/tink-go/v2/proto/tink_go_proto"
)
const (
// HPKE key lengths from
// https://www.rfc-editor.org/rfc/rfc9180.html#section-7.1.
hpkeX25519HKDFSHA256PrivKeyLen = 32
hpkeX25519HKDFSHA256PubKeyLen = 32
hpkePrivateKeyTypeURL = "type.googleapis.com/google.crypto.tink.HpkePrivateKey"
)
// KeysetHandleFromSerializedPrivateKey returns a keyset handle containing a
// primary key that has the specified privKeyBytes and pubKeyBytes and matches
// template.
//
// Supported templates include:
// - DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_CHACHA20_POLY1305_Raw_Key_Template,
// which requires privKeyBytes and pubKeyBytes to be the KEM-encoding of the
// private and public key, respectively, i.e. SerializePrivateKey and
// SerializePublicKey in
// https://www.rfc-editor.org/rfc/rfc9180.html#section-7.1.1.
func KeysetHandleFromSerializedPrivateKey(privKeyBytes, pubKeyBytes []byte, template *tinkpb.KeyTemplate) (*keyset.Handle, error) {
params, err := hpkeParamsFromTemplate(template)
if err != nil {
return nil, fmt.Errorf("failed to verify key template: %v", err)
}
if len(privKeyBytes) != hpkeX25519HKDFSHA256PrivKeyLen {
return nil, fmt.Errorf("privKeyBytes length is %d but should be %d", len(privKeyBytes), hpkeX25519HKDFSHA256PrivKeyLen)
}
if len(pubKeyBytes) != hpkeX25519HKDFSHA256PubKeyLen {
return nil, fmt.Errorf("pubKeyBytes length is %d but should be %d", len(pubKeyBytes), hpkeX25519HKDFSHA256PubKeyLen)
}
privKey := &hpkepb.HpkePrivateKey{
Version: 0,
PrivateKey: privKeyBytes,
PublicKey: &hpkepb.HpkePublicKey{
Version: 0,
Params: params,
PublicKey: pubKeyBytes,
},
}
serializedPrivKey, err := proto.Marshal(privKey)
if err != nil {
return nil, fmt.Errorf("failed to marshal HpkePrivateKey %v: %v", privKey, err)
}
ks := &tinkpb.Keyset{
PrimaryKeyId: 1,
Key: []*tinkpb.Keyset_Key{
{
KeyData: &tinkpb.KeyData{
TypeUrl: hpkePrivateKeyTypeURL,
Value: serializedPrivKey,
KeyMaterialType: tinkpb.KeyData_ASYMMETRIC_PRIVATE,
},
Status: tinkpb.KeyStatusType_ENABLED,
KeyId: 1,
OutputPrefixType: tinkpb.OutputPrefixType_RAW,
},
},
}
return testkeyset.NewHandle(ks)
}
// hpkeParamsFromTemplate returns HPKE params after verifying that template is
// supported.
//
// Supported templates include:
// - DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_CHACHA20_POLY1305_Raw_Key_Template.
func hpkeParamsFromTemplate(template *tinkpb.KeyTemplate) (*hpkepb.HpkeParams, error) {
if template.GetTypeUrl() != hpkePrivateKeyTypeURL {
return nil, fmt.Errorf("not key type URL %s", hpkePrivateKeyTypeURL)
}
if template.GetOutputPrefixType() != tinkpb.OutputPrefixType_RAW {
return nil, errors.New("not raw output prefix type")
}
keyFormat := &hpkepb.HpkeKeyFormat{}
if err := proto.Unmarshal(template.GetValue(), keyFormat); err != nil {
return nil, fmt.Errorf("failed to unmarshal HpkeKeyFormat(%v): %v", template.GetValue(), err)
}
params := keyFormat.GetParams()
if kem := params.GetKem(); kem != hpkepb.HpkeKem_DHKEM_X25519_HKDF_SHA256 {
return nil, fmt.Errorf("HPKE KEM %s not supported", kem)
}
if kdf := params.GetKdf(); kdf != hpkepb.HpkeKdf_HKDF_SHA256 {
return nil, fmt.Errorf("HPKE KDF %s not supported", kdf)
}
if aead := params.GetAead(); aead != hpkepb.HpkeAead_CHACHA20_POLY1305 {
return nil, fmt.Errorf("HPKE AEAD %s not supported", aead)
}
return params, nil
}
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