/*
 * nimbus-jose-jwt
 *
 * Copyright 2012-2016, Connect2id Ltd and contributors.
 *
 * 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.nimbusds.jose.crypto.impl;


import javax.crypto.SecretKey;

import com.nimbusds.jose.JOSEException;
import net.jcip.annotations.ThreadSafe;
import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.InvalidCipherTextException;
import org.bouncycastle.crypto.engines.AESEngine;
import org.bouncycastle.crypto.modes.GCMBlockCipher;
import org.bouncycastle.crypto.params.AEADParameters;
import org.bouncycastle.crypto.params.KeyParameter;


/**
 * Legacy AES/GSM/NoPadding encryption and decryption methods. Uses the
 * BouncyCastle.org API. This class is thread-safe.
 *
 * @author Vladimir Dzhuvinov
 * @author Axel Nennker
 * @version 2015-11-15
 */
@ThreadSafe
public class LegacyAESGCM {


        /**
         * The standard authentication tag length (128 bits).
         */
        public static final int AUTH_TAG_BIT_LENGTH = 128;


        /**
         * Creates a new AES cipher.
         *
         * @param secretKey     The AES key. Must not be {@code null}.
         * @param forEncryption If {@code true} creates an AES encryption
         *                      cipher, else creates an AES decryption
         *                      cipher.
         *
         * @return The AES cipher.
         */
        public static AESEngine createAESCipher(final SecretKey secretKey,
                                                final boolean forEncryption) {

                AESEngine cipher = new AESEngine();

                CipherParameters cipherParams = new KeyParameter(secretKey.getEncoded());

                cipher.init(forEncryption, cipherParams);

                return cipher;
        }


        /**
         * Creates a new AES/GCM/NoPadding cipher.
         *
         * @param secretKey     The AES key. Must not be {@code null}.
         * @param forEncryption If {@code true} creates an encryption cipher,
         *                      else creates a decryption cipher.
         * @param iv            The initialisation vector (IV). Must not be
         *                      {@code null}.
         * @param authData      The authenticated data. Must not be
         *                      {@code null}.
         *
         * @return The AES/GCM/NoPadding cipher.
         */
        private static GCMBlockCipher createAESGCMCipher(final SecretKey secretKey,
                                                         final boolean forEncryption,
                                                         final byte[] iv,
                                                         final byte[] authData) {

                // Initialise AES cipher
                BlockCipher cipher = createAESCipher(secretKey, forEncryption);

                // Create GCM cipher with AES
                GCMBlockCipher gcm = new GCMBlockCipher(cipher);

                AEADParameters aeadParams = new AEADParameters(new KeyParameter(secretKey.getEncoded()),
                        AUTH_TAG_BIT_LENGTH,
                        iv,
                        authData);
                gcm.init(forEncryption, aeadParams);

                return gcm;
        }


        /**
         * Encrypts the specified plain text using AES/GCM/NoPadding.
         *
         * @param secretKey The AES key. Must not be {@code null}.
         * @param plainText The plain text. Must not be {@code null}.
         * @param iv        The initialisation vector (IV). Must not be
         *                  {@code null}.
         * @param authData  The authenticated data. Must not be {@code null}.
         *
         * @return The authenticated cipher text.
         *
         * @throws JOSEException If encryption failed.
         */
        public static AuthenticatedCipherText encrypt(final SecretKey secretKey,
                                                      final byte[] iv,
                                                      final byte[] plainText,
                                                      final byte[] authData)
                throws JOSEException {

                // Initialise AES/GCM cipher for encryption
                GCMBlockCipher cipher = createAESGCMCipher(secretKey, true, iv, authData);


                // Prepare output buffer
                int outputLength = cipher.getOutputSize(plainText.length);
                byte[] output = new byte[outputLength];


                // Produce cipher text
                int outputOffset = cipher.processBytes(plainText, 0, plainText.length, output, 0);


                // Produce authentication tag
                try {
                        outputOffset += cipher.doFinal(output, outputOffset);

                } catch (InvalidCipherTextException e) {

                        throw new JOSEException("Couldn't generate GCM authentication tag: " + e.getMessage(), e);
                }

                // Split output into cipher text and authentication tag
                int authTagLength = AUTH_TAG_BIT_LENGTH / 8;

                byte[] cipherText = new byte[outputOffset - authTagLength];
                byte[] authTag = new byte[authTagLength];

                System.arraycopy(output, 0, cipherText, 0, cipherText.length);
                System.arraycopy(output, outputOffset - authTagLength, authTag, 0, authTag.length);

                return new AuthenticatedCipherText(cipherText, authTag);
        }


        /**
         * Decrypts the specified cipher text using AES/GCM/NoPadding.
         *
         * @param secretKey  The AES key. Must not be {@code null}.
         * @param iv         The initialisation vector (IV). Must not be
         *                   {@code null}.
         * @param cipherText The cipher text. Must not be {@code null}.
         * @param authData   The authenticated data. Must not be {@code null}.
         * @param authTag    The authentication tag. Must not be {@code null}.
         *
         * @return The decrypted plain text.
         *
         * @throws JOSEException If decryption failed.
         */
        public static byte[] decrypt(final SecretKey secretKey,
                                     final byte[] iv,
                                     final byte[] cipherText,
                                     final byte[] authData,
                                     final byte[] authTag)
                throws JOSEException {

                // Initialise AES/GCM cipher for decryption
                GCMBlockCipher cipher = createAESGCMCipher(secretKey, false, iv, authData);


                // Join cipher text and authentication tag to produce cipher input
                byte[] input = new byte[cipherText.length + authTag.length];

                System.arraycopy(cipherText, 0, input, 0, cipherText.length);
                System.arraycopy(authTag, 0, input, cipherText.length, authTag.length);

                int outputLength = cipher.getOutputSize(input.length);

                byte[] output = new byte[outputLength];


                // Decrypt
                int outputOffset = cipher.processBytes(input, 0, input.length, output, 0);

                // Validate authentication tag
                try {
                        outputOffset += cipher.doFinal(output, outputOffset);

                } catch (InvalidCipherTextException e) {

                        throw new JOSEException("Couldn't validate GCM authentication tag: " + e.getMessage(), e);
                }

                return output;
        }


        /**
         * Prevents public instantiation.
         */
        private LegacyAESGCM() { }
}