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

import java.nio.ByteBuffer;
import java.security.SecureRandom;
import java.util.Arrays;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import org.jboss.resteasy.jose.i18n.Messages;

/**
 * AES/CBC/PKCS5Padding and AES/CBC/PKCS5Padding/HMAC-SHA2 encryption and
 * decryption methods.
 *
 * <p>
 * See draft-ietf-jose-json-web-algorithms-10, section 4.8.3.
 *
 * @author Vladimir Dzhuvinov
 * @author Axel Nennker
 * @version $version$ (2013-05-07)
 */
class AESCBC {

    /**
     * The standard Initialisation Vector (IV) length (128 bits).
     */
    public static final int IV_BIT_LENGTH = 128;

    /**
     * Generates a random 128 bit (16 byte) Initialisation Vector(IV) for
     * use in AES-CBC encryption.
     *
     * @param randomGen The secure random generator to use. Must be
     *                  correctly initialised and not {@code null}.
     *
     * @return The random 128 bit IV, as 16 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/CBC/PKCS5Padding 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}.
     *
     * @return The AES/CBC/PKCS5Padding cipher.
     */
    private static Cipher createAESCBCCipher(final SecretKey secretKey,
            final boolean forEncryption,
            final byte[] iv)
            throws RuntimeException {

        Cipher cipher;

        try {
            cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

            SecretKeySpec keyspec = new SecretKeySpec(secretKey.getEncoded(), "AES");

            IvParameterSpec ivSpec = new IvParameterSpec(iv);

            if (forEncryption) {

                cipher.init(Cipher.ENCRYPT_MODE, keyspec, ivSpec);

            } else {

                cipher.init(Cipher.DECRYPT_MODE, keyspec, ivSpec);
            }

        } catch (Exception e) {

            throw new RuntimeException(e.getMessage(), e);
        }

        return cipher;
    }

    /**
     * Encrypts the specified plain text using AES/CBC/PKCS5Padding.
     *
     * @param secretKey The AES key. Must not be {@code null}.
     * @param iv        The initialisation vector (IV). Must not be
     *                  {@code null}.
     * @param plainText The plain text. Must not be {@code null}.
     *
     * @return The cipher text.
     *
     * @throws RuntimeException If encryption failed.
     */
    public static byte[] encrypt(final SecretKey secretKey,
            final byte[] iv,
            final byte[] plainText)
            throws RuntimeException {

        Cipher cipher = createAESCBCCipher(secretKey, true, iv);

        try {
            return cipher.doFinal(plainText);

        } catch (Exception e) {

            throw new RuntimeException(e.getMessage(), e);
        }
    }

    /**
     * Computes the bit length of the specified Additional Authenticated
     * Data (AAD). Used in AES/CBC/PKCS5Padding/HMAC-SHA2 encryption.
     *
     * @param aad The Additional Authenticated Data (AAD). Must not be
     *            {@code null}.
     *
     * @return The computed AAD bit length, as a 64 bit big-ending
     *         representation (8 byte array).
     */
    public static byte[] computeAADLength(final byte[] aad) {

        final int bitLength = aad.length * 8;

        return ByteBuffer.allocate(8).putLong(bitLength).array();
    }

    /**
     * Encrypts the specified plain text using AES/CBC/PKCS5Padding/
     * HMAC-SHA2.
     *
     * <p>
     * See draft-ietf-jose-json-web-algorithms-10, section 4.8.2.
     *
     * <p>
     * See draft-mcgrew-aead-aes-cbc-hmac-sha2-01
     *
     * @param secretKey The secret key. Must be 256 or 512 bits long. Must
     *                  not be {@code null}.
     * @param iv        The initialisation vector (IV). Must not be
     *                  {@code null}.
     * @param plainText The plain text. Must not be {@code null}.
     * @param aad       The additional authenticated data. Must not be
     *                  {@code null}.
     *
     * @return The authenticated cipher text.
     *
     * @throws RuntimeException If encryption failed.
     */
    public static AuthenticatedCipherText encryptAuthenticated(final SecretKey secretKey,
            final byte[] iv,
            final byte[] plainText,
            final byte[] aad)
            throws RuntimeException {

        // Extract MAC + AES/CBC keys from input secret key
        CompositeKey compositeKey = new CompositeKey(secretKey);

        // Encrypt plain text
        byte[] cipherText = encrypt(compositeKey.getAESKey(), iv, plainText);

        // AAD length to 8 byte array
        byte[] al = computeAADLength(aad);

        // Do MAC
        int hmacInputLength = aad.length + iv.length + cipherText.length + al.length;
        byte[] hmacInput = ByteBuffer.allocate(hmacInputLength).put(aad).put(iv).put(cipherText).put(al).array();

        byte[] hmac = HMAC.compute(compositeKey.getMACKey(), hmacInput);

        byte[] authTag = Arrays.copyOf(hmac, compositeKey.getTruncatedMACByteLength());

        return new AuthenticatedCipherText(cipherText, authTag);
    }

    /**
     * Decrypts the specified cipher text using AES/CBC/PKCS5Padding.
     *
     * @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}.
     *
     * @return The decrypted plain text.
     *
     * @throws RuntimeException If decryption failed.
     */
    public static byte[] decrypt(final SecretKey secretKey,
            final byte[] iv,
            final byte[] cipherText)
            throws RuntimeException {

        Cipher cipher = createAESCBCCipher(secretKey, false, iv);

        try {
            return cipher.doFinal(cipherText);

        } catch (Exception e) {

            throw new RuntimeException(e.getMessage(), e);
        }
    }

    /**
     * Decrypts the specified plain text using AES/CBC/PKCS5Padding/
     * HMAC-SHA2.
     *
     * <p>
     * See draft-ietf-jose-json-web-algorithms-10, section 4.8.2.
     *
     * <p>
     * See draft-mcgrew-aead-aes-cbc-hmac-sha2-01
     *
     * @param secretKey  The secret key. Must be 256 or 512 bits long. 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 aad        The additional 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[] decryptAuthenticated(final SecretKey secretKey,
            final byte[] iv,
            final byte[] cipherText,
            final byte[] aad,
            final byte[] authTag)
            throws RuntimeException {

        // Extract MAC + AES/CBC keys from input secret key
        CompositeKey compositeKey = new CompositeKey(secretKey);

        // AAD length to 8 byte array
        byte[] al = computeAADLength(aad);

        // Check MAC
        int hmacInputLength = aad.length + iv.length + cipherText.length + al.length;
        byte[] hmacInput = ByteBuffer.allocate(hmacInputLength).put(aad).put(iv).put(cipherText).put(al).array();

        byte[] hmac = HMAC.compute(compositeKey.getMACKey(), hmacInput);

        byte[] expectedAuthTag = Arrays.copyOf(hmac, compositeKey.getTruncatedMACByteLength());

        boolean macCheckPassed = true;

        if (!org.bouncycastle.util.Arrays.constantTimeAreEqual(expectedAuthTag, authTag)) {
            // Thwart timing attacks by delaying exception until after decryption
            macCheckPassed = false;
        }

        byte[] plainText = decrypt(compositeKey.getAESKey(), iv, cipherText);

        if (!macCheckPassed) {

            throw new RuntimeException(Messages.MESSAGES.macCheckFailed());
        }

        return plainText;
    }

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