/**
 * Implementation of the Tiny Encryption Algorithm (TEA).
 * The Tiny Encryption Algorithm is one of the fastest and most efficient
 * cryptographic algorithms in existence. It was developed by David Wheeler and
 * Roger Needham at the Computer Laboratory of Cambridge University.
 *
 * See http://www.cl.cam.ac.uk/ftp/users/djw3/tea.ps
 *
 * This software was written to provide simple encryption for J2ME.
 * The homepage for this software is http://winterwell.com/software/TEA.php
 *
 * (c) 2008 Joe Halliwell <joe.halliwell@gmail.com>
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

public class TEA {
	private final static int SUGAR = 0x9E3779B9;
	private final static int CUPS  = 32;
	private final static int UNSUGAR = 0xC6EF3720;

	private int[] S = new int[4];

	/**
	 * Initialize the cipher for encryption or decryption.
	 * @param key a 16 byte (128-bit) key
	 */
	public TEA(byte[] key) {
		if (key == null)
			throw new RuntimeException("Invalid key: Key was null");
		if (key.length < 16)
			throw new RuntimeException("Invalid key: Length was less than 16 bytes");
		for (int off=0, i=0; i<4; i++) {
			S[i] = ((key[off++] & 0xff)) |
			((key[off++] & 0xff) <<  8) |
			((key[off++] & 0xff) << 16) |
			((key[off++] & 0xff) << 24);
		}
	}

	/**
	 * Encrypt an array of bytes.
	 * @param clear the cleartext to encrypt
	 * @return the encrypted text
	 */
	public byte[] encrypt(byte[] clear) {
		int paddedSize = ((clear.length/8) + (((clear.length%8)==0)?0:1)) * 2;
		int[] buffer = new int[paddedSize + 1];
		buffer[0] = clear.length;
		pack(clear, buffer, 1);
		brew(buffer);
		return unpack(buffer, 0, buffer.length * 4);
	}

	/**
	 * Decrypt an array of bytes.
	 * @param ciper the cipher text to decrypt
	 * @return the decrypted text
	 */
	public byte[] decrypt(byte[] crypt) {
		assert crypt.length % 4 == 0;
		assert (crypt.length / 4) % 2 == 1;
		int[] buffer = new int[crypt.length / 4];
		pack(crypt, buffer, 0);
		unbrew(buffer);
		return unpack(buffer, 1, buffer[0]);
	}

	void brew(int[] buf) {
		assert buf.length % 2 == 1;
		int i, v0, v1, sum, n;
		i = 1;
		while (i<buf.length) {
			n = CUPS;
			v0 = buf[i];
			v1 = buf[i+1];
			sum = 0;
			while (n-->0) {
				sum += SUGAR;
				v0  += ((v1 << 4 ) + S[0] ^ v1) + (sum ^ (v1 >>> 5)) + S[1];
				v1  += ((v0 << 4 ) + S[2] ^ v0) + (sum ^ (v0 >>> 5)) + S[3];
			}
			buf[i] = v0;
			buf[i+1] = v1;
			i+=2;
		}
	}
	
	void unbrew(int[] buf) {
		assert buf.length % 2 == 1;
		int i, v0, v1, sum, n;
		i = 1;
		while (i<buf.length) {
			n = CUPS;
			v0 = buf[i]; 
			v1 = buf[i+1];
			sum = UNSUGAR;
			while (n--> 0) {
				v1  -= ((v0 << 4 ) + S[2] ^ v0) + (sum ^ (v0 >>> 5)) + S[3];
				v0  -= ((v1 << 4 ) + S[0] ^ v1) + (sum ^ (v1 >>> 5)) + S[1];
				sum -= SUGAR;
			}
			buf[i] = v0;
			buf[i+1] = v1;
			i+=2;
		}
	}
	
	void pack(byte[] src, int[] dest, int destOffset) {
		assert destOffset + (src.length / 4) <= dest.length;
		int i = 0, shift = 24;
		int j = destOffset;
		dest[j] = 0;
		while (i<src.length) {
			dest[j] |= ((src[i] & 0xff) << shift);
			if (shift==0) {
				shift = 24;
				j++;
				if (j<dest.length) dest[j] = 0;
			}
			else {
				shift -= 8;
			}
			i++;
		}
	}
	
	byte[] unpack(int[] src, int srcOffset, int destLength) {
		assert destLength <= (src.length - srcOffset) * 4;
		byte[] dest = new byte[destLength];
		int i = srcOffset;
		int count = 0;
		for (int j = 0; j < destLength; j++) {
			dest[j] = (byte) ((src[i] >> (24 - (8*count))) & 0xff);
			count++;
			if (count == 4) {
				count = 0;
				i++;
			}
		}
		return dest;
	}

	/* Simple usage example */
	public static String quote = "Now rise, and show your strength. Be eloquent, and deep, and tender; see, with a clear eye, into Nature, and into life:  spread your white wings of quivering thought, and soar, a god-like spirit, over the whirling world beneath you, up through long lanes of flaming stars to the gates of eternity!";
	
	public static void main(String[] args) {
		/* Create a cipher using the first 16 bytes of the passphrase */
		TEA tea = new TEA("And is there honey still for tea?".getBytes());

		byte[] original = quote.getBytes();

		/* Run it through the cipher... and back */
		byte[] crypt = tea.encrypt(original);
		byte[] result = tea.decrypt(crypt);

		/* Ensure that all went well */
        String test = new String(result);
        if (!test.equals(quote))
		    throw new RuntimeException("Fail");
	}
}