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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 aesgcmsiv
import (
"bytes"
"fmt"
"slices"
"github.com/tink-crypto/tink-go/v2/aead/subtle"
"github.com/tink-crypto/tink-go/v2/insecuresecretdataaccess"
"github.com/tink-crypto/tink-go/v2/key"
"github.com/tink-crypto/tink-go/v2/tink"
)
type aead struct {
rawAEAD *subtle.AESGCMSIV
prefix []byte
variant Variant
}
var _ tink.AEAD = (*aead)(nil)
func newAEAD(key *Key) (tink.AEAD, error) {
rawAEAD, err := subtle.NewAESGCMSIV(key.KeyBytes().Data(insecuresecretdataaccess.Token{}))
if err != nil {
return nil, err
}
return &aead{
rawAEAD: rawAEAD,
prefix: key.OutputPrefix(),
variant: key.parameters.Variant(),
}, nil
}
// Encrypt encrypts plaintext with associatedData.
func (ca *aead) Encrypt(plaintext []byte, associatedData []byte) ([]byte, error) {
ciphertext, err := ca.rawAEAD.Encrypt(plaintext, associatedData)
if err != nil {
return nil, err
}
return slices.Concat(ca.prefix, ciphertext), nil
}
// Decrypt decrypts ciphertext with associatedData.
func (ca *aead) Decrypt(ciphertext []byte, associatedData []byte) ([]byte, error) {
if !bytes.HasPrefix(ciphertext, ca.prefix) {
return nil, fmt.Errorf("aes_gcm_siv: ciphertext has invalid prefix")
}
toDecrypt := ciphertext[len(ca.prefix):]
plaintext, err := ca.rawAEAD.Decrypt(toDecrypt, associatedData)
if err != nil {
return nil, err
}
return plaintext, nil
}
func primitiveConstructor(key key.Key) (any, error) {
that, ok := key.(*Key)
if !ok {
return nil, fmt.Errorf("aes_gcm_siv: invalid key type: got %T, want *aesgcmsiv.Key", key)
}
return newAEAD(that)
}
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