// 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;

import java.security.GeneralSecurityException;

/**
 * Interface for Authenticated Encryption with Associated Data (AEAD).
 *
 * <h3>Security guarantees</h3>
 *
 * <p>Implementations of this interface are secure against adaptive chosen ciphertext attacks.
 * Encryption with associated data ensures authenticity (who the sender is) and integrity (the data
 * has not been tampered with) of that data, but not its secrecy. (see <a
 * href="https://tools.ietf.org/html/rfc5116">RFC 5116</a> for more info)
 *
 * @since 1.0.0
 */
public interface Aead {
  /**
   * Encrypts {@code plaintext} with {@code associatedData} as associated authenticated data.
   * The resulting ciphertext allows for checking authenticity and integrity of associated data
   * ({@code associatedData}), but does not guarantee its secrecy.
   *
   * @param plaintext       the plaintext to be encrypted. It must be non-null, but can also
   *                        be an empty (zero-length) byte array
   * @param associatedData  associated data to be authenticated, but not encrypted.  Associated data
   *                        is optional, so this parameter can be null.  In this case the null value
   *                        is equivalent to an empty (zero-length) byte array.
   *                        For successful decryption the same associatedData must be provided
   *                        along with the ciphertext.
   * @return resulting ciphertext
   */
  byte[] encrypt(final byte[] plaintext, final byte[] associatedData)
      throws GeneralSecurityException;

  /**
   * Decrypts {@code ciphertext} with {@code associatedData} as associated authenticated data. The
   * decryption verifies the authenticity and integrity of the associated data, but there are no
   * guarantees wrt. secrecy of that data.
   *
   * @param ciphertext the plaintext to be decrypted. It must be non-null.
   * @param associatedData associated data to be authenticated. For successful decryption it must be
   *     the same as associatedData used during encryption. Can be null, which is equivalent to an
   *     empty (zero-length) byte array.
   * @return resulting plaintext
   * @throws GeneralSecurityException if decryption fails. Decryption must fail if {@code
   *     ciphertext} is not correctly authenticated for the given {@code associatedData}.
   */
  byte[] decrypt(final byte[] ciphertext, final byte[] associatedData)
      throws GeneralSecurityException;
}