package org.jboss.resteasy.jose.jwe.crypto;

import java.security.SecureRandom;

import javax.crypto.SecretKey;

import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.InvalidCipherTextException;
import org.bouncycastle.crypto.modes.GCMBlockCipher;
import org.bouncycastle.crypto.params.AEADParameters;
import org.bouncycastle.crypto.params.KeyParameter;
import org.jboss.resteasy.jose.i18n.Messages;

/**
 * AES/GSM/NoPadding encryption and decryption methods. Uses the
 * BouncyCastle.org provider.
 *
 * <p>
 * See draft-ietf-jose-json-web-algorithms-10, section 4.9.
 *
 * @author Vladimir Dzhuvinov
 * @author Axel Nennker
 * @version $version$ (2013-05-07)
 */
class AESGCM {

    /**
     * The standard Initialisation Vector (IV) length (96 bits).
     */
    public static final int IV_BIT_LENGTH = 96;

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

    /**
     * Generates a random 96 bit (12 byte) Initialisation Vector(IV) for
     * use in AES-GCM encryption.
     *
     * <p>
     * See draft-ietf-jose-json-web-algorithms-08, section-4.9.
     *
     * @param randomGen The secure random generator to use. Must be
     *                  correctly initialised and not {@code null}.
     *
     * @return The random 96 bit IV, as 12 byte array.
     */
    public static byte[] generateIV(final SecureRandom randomGen) {

        byte[] bytes = new byte[IV_BIT_LENGTH / 8];
        randomGen.nextBytes(bytes);
        return bytes;
    }

    /**
     * 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 = AES.createCipher(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 RuntimeException If encryption failed.
     */
    public static AuthenticatedCipherText encrypt(final SecretKey secretKey,
            final byte[] iv,
            final byte[] plainText,
            final byte[] authData)
            throws RuntimeException {

        // 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 RuntimeException(Messages.MESSAGES.couldntGenerateGCMAuthentication(e.getLocalizedMessage()), 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 RuntimeException If decryption failed.
     */
    public static byte[] decrypt(final SecretKey secretKey,
            final byte[] iv,
            final byte[] cipherText,
            final byte[] authData,
            final byte[] authTag)
            throws RuntimeException {

        // 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 RuntimeException(Messages.MESSAGES.couldntValidateGCMAuthentication(e.getLocalizedMessage()), e);
        }

        return output;
    }

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