java_src/src/main/java/com/google/crypto/tink/subtle/ChaCha20Poly1305.java

// Copyright 2017 Google Inc.
//
// 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 com.google.crypto.tink.subtle;

import com.google.crypto.tink.Aead;
import com.google.crypto.tink.aead.internal.InsecureNonceChaCha20Poly1305;
import com.google.crypto.tink.aead.internal.Poly1305;
import java.nio.ByteBuffer;
import java.security.GeneralSecurityException;
import java.util.Arrays;

/**
 * ChaCha20Poly1305 AEAD construction, as described in <a
 * href="https://tools.ietf.org/html/rfc8439#section-2.8">RFC 8439, section 2.8</a>.
 *
 * @since 1.1.0
 */
public final class ChaCha20Poly1305 implements Aead {
  private final InsecureNonceChaCha20Poly1305 cipher;

  public ChaCha20Poly1305(final byte[] key) throws GeneralSecurityException {
    cipher = new InsecureNonceChaCha20Poly1305(key);
  }

  @Override
  public byte[] encrypt(final byte[] plaintext, final byte[] associatedData)
      throws GeneralSecurityException {
    ByteBuffer output =
        ByteBuffer.allocate(
            ChaCha20.NONCE_LENGTH_IN_BYTES + plaintext.length + Poly1305.MAC_TAG_SIZE_IN_BYTES);
    byte[] nonce = Random.randBytes(ChaCha20.NONCE_LENGTH_IN_BYTES);
    output.put(nonce); // Prepend nonce to ciphertext output.
    cipher.encrypt(output, nonce, plaintext, associatedData);
    return output.array();
  }

  @Override
  public byte[] decrypt(final byte[] ciphertext, final byte[] associatedData)
      throws GeneralSecurityException {
    if (ciphertext.length < ChaCha20.NONCE_LENGTH_IN_BYTES + Poly1305.MAC_TAG_SIZE_IN_BYTES) {
      throw new GeneralSecurityException("ciphertext too short");
    }
    byte[] nonce = Arrays.copyOf(ciphertext, ChaCha20.NONCE_LENGTH_IN_BYTES);
    ByteBuffer rawCiphertext =
        ByteBuffer.wrap(
            ciphertext,
            ChaCha20.NONCE_LENGTH_IN_BYTES,
            ciphertext.length - ChaCha20.NONCE_LENGTH_IN_BYTES);
    return cipher.decrypt(rawCiphertext, nonce, associatedData);
  }
}