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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 aead
import (
"errors"
"fmt"
"golang.org/x/crypto/chacha20poly1305"
)
const (
// ChaCha20Poly1305InsecureNonceSize is the size of the nonce.
ChaCha20Poly1305InsecureNonceSize = chacha20poly1305.NonceSize
// ChaCha20Poly1305InsecureTagSize is the size of the tag.
ChaCha20Poly1305InsecureTagSize = chacha20poly1305.Overhead
maxPlaintextSize = maxInt - ChaCha20Poly1305InsecureNonceSize - ChaCha20Poly1305InsecureTagSize
)
// ChaCha20Poly1305InsecureNonce is an insecure implementation of the AEAD
// interface that permits the user to set the nonce.
type ChaCha20Poly1305InsecureNonce struct {
Key []byte
}
// NewChaCha20Poly1305InsecureNonce returns a ChaCha20Poly1305InsecureNonce instance.
// The key argument should be a 32-bytes key.
func NewChaCha20Poly1305InsecureNonce(key []byte) (*ChaCha20Poly1305InsecureNonce, error) {
if len(key) != chacha20poly1305.KeySize {
return nil, errors.New("bad key length")
}
return &ChaCha20Poly1305InsecureNonce{Key: key}, nil
}
// Encrypt encrypts plaintext with nonce and associatedData.
func (ca *ChaCha20Poly1305InsecureNonce) Encrypt(dst, nonce, plaintext, associatedData []byte) ([]byte, error) {
if len(plaintext) > maxPlaintextSize {
return nil, fmt.Errorf("plaintext too long")
}
c, err := chacha20poly1305.New(ca.Key)
if err != nil {
return nil, err
}
return c.Seal(dst, nonce, plaintext, associatedData), nil
}
// Decrypt decrypts ciphertext with nonce and associatedData.
func (ca *ChaCha20Poly1305InsecureNonce) Decrypt(nonce, ciphertext, associatedData []byte) ([]byte, error) {
if len(nonce) != ChaCha20Poly1305InsecureNonceSize {
return nil, fmt.Errorf("invalid nonce length: got %d, want %d", len(nonce), ChaCha20Poly1305InsecureNonceSize)
}
if len(ciphertext) < ChaCha20Poly1305InsecureTagSize {
return nil, fmt.Errorf("ciphertext too short")
}
c, err := chacha20poly1305.New(ca.Key)
if err != nil {
return nil, err
}
return c.Open(nil, nonce, ciphertext, associatedData)
}
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