MD4Digest.java

package fi.codecrew.moya.utilities;

import java.security.MessageDigest;

public class MD4Digest extends MessageDigest {
	/**
	 * The size in bytes of the input block to the tranformation algorithm.
	 */
	private static final int BLOCK_LENGTH = 64; //    = 512 / 8;

	/**
	 * 4 32-bit words (interim result)
	 */
	private int[] context = new int[4];

	/**
	 * Number of bytes processed so far mod. 2 power of 64.
	 */
	private long count;

	/**
	 * 512 bits input buffer = 16 x 32-bit words holds until reaches 512 bits.
	 */
	private byte[] buffer = new byte[BLOCK_LENGTH];

	/**
	 * 512 bits work buffer = 16 x 32-bit words
	 */
	private int[] X = new int[16];

	public MD4Digest() {
		super("MD4");
		engineReset();
	}

	@Override
	public void engineUpdate(byte b) {
		int i = (int) (count % BLOCK_LENGTH);
		count++;
		buffer[i] = b;
		if (i == BLOCK_LENGTH - 1)
			transform(buffer, 0);

	}

	@Override
	protected void engineUpdate(byte[] input, int offset, int len) {
		// make sure we don't exceed input's allocated size/length
		if (offset < 0 || len < 0 || (long) offset + len > input.length)
			throw new ArrayIndexOutOfBoundsException();

		// compute number of bytes still unhashed; ie. present in buffer
		int bufferNdx = (int) (count % BLOCK_LENGTH);
		count += len; // update number of bytes
		int partLen = BLOCK_LENGTH - bufferNdx;
		int i = 0;
		if (len >= partLen) {
			System.arraycopy(input, offset, buffer, bufferNdx, partLen);

			transform(buffer, 0);

			for (i = partLen; i + BLOCK_LENGTH - 1 < len; i += BLOCK_LENGTH)
				transform(input, offset + i);
			bufferNdx = 0;
		}
		// buffer remaining input
		if (i < len)
			System.arraycopy(input, offset + i, buffer, bufferNdx, len - i);

	}

	@Override
	protected byte[] engineDigest() {
		// pad output to 56 mod 64; as RFC1320 puts it: congruent to 448 mod 512
		int bufferNdx = (int) (count % BLOCK_LENGTH);
		int padLen = (bufferNdx < 56) ? (56 - bufferNdx) : (120 - bufferNdx);

		// padding is alwas binary 1 followed by binary 0s
		byte[] tail = new byte[padLen + 8];
		tail[0] = (byte) 0x80;

		// append length before final transform:
		// save number of bits, casting the long to an array of 8 bytes
		// save low-order byte first.
		for (int i = 0; i < 8; i++)
			tail[padLen + i] = (byte) ((count * 8) >>> (8 * i));

		engineUpdate(tail, 0, tail.length);

		byte[] result = new byte[16];
		// cast this MD4's context (array of 4 ints) into an array of 16 bytes.
		for (int i = 0; i < 4; i++)
			for (int j = 0; j < 4; j++)
				result[i * 4 + j] = (byte) (context[i] >>> (8 * j));

		// reset the engine
		engineReset();
		return result;
	}

	@Override
	protected void engineReset() {
		// initial values of MD4 i.e. A, B, C, D
		// as per rfc-1320; they are low-order byte first
		context[0] = 0x67452301;
		context[1] = 0xEFCDAB89;
		context[2] = 0x98BADCFE;
		context[3] = 0x10325476;
		count = 0L;
		for (int i = 0; i < BLOCK_LENGTH; i++)
			buffer[i] = 0;

	}

	/**
	 * MD4 basic transformation.
	 * <p>
	 * Transforms context based on 512 bits from input block starting from the offset'th byte.
	 * 
	 * @param block
	 *            input sub-array.
	 * @param offset
	 *            starting position of sub-array.
	 */
	private void transform(byte[] block, int offset) {

		// encodes 64 bytes from input block into an array of 16 32-bit
		// entities. Use A as a temp var.
		for (int i = 0; i < 16; i++)
			X[i] = (block[offset++] & 0xFF) |
					(block[offset++] & 0xFF) << 8 |
					(block[offset++] & 0xFF) << 16 |
					(block[offset++] & 0xFF) << 24;

		int A = context[0];
		int B = context[1];
		int C = context[2];
		int D = context[3];

		A = FF(A, B, C, D, X[0], 3);
		D = FF(D, A, B, C, X[1], 7);
		C = FF(C, D, A, B, X[2], 11);
		B = FF(B, C, D, A, X[3], 19);
		A = FF(A, B, C, D, X[4], 3);
		D = FF(D, A, B, C, X[5], 7);
		C = FF(C, D, A, B, X[6], 11);
		B = FF(B, C, D, A, X[7], 19);
		A = FF(A, B, C, D, X[8], 3);
		D = FF(D, A, B, C, X[9], 7);
		C = FF(C, D, A, B, X[10], 11);
		B = FF(B, C, D, A, X[11], 19);
		A = FF(A, B, C, D, X[12], 3);
		D = FF(D, A, B, C, X[13], 7);
		C = FF(C, D, A, B, X[14], 11);
		B = FF(B, C, D, A, X[15], 19);

		A = GG(A, B, C, D, X[0], 3);
		D = GG(D, A, B, C, X[4], 5);
		C = GG(C, D, A, B, X[8], 9);
		B = GG(B, C, D, A, X[12], 13);
		A = GG(A, B, C, D, X[1], 3);
		D = GG(D, A, B, C, X[5], 5);
		C = GG(C, D, A, B, X[9], 9);
		B = GG(B, C, D, A, X[13], 13);
		A = GG(A, B, C, D, X[2], 3);
		D = GG(D, A, B, C, X[6], 5);
		C = GG(C, D, A, B, X[10], 9);
		B = GG(B, C, D, A, X[14], 13);
		A = GG(A, B, C, D, X[3], 3);
		D = GG(D, A, B, C, X[7], 5);
		C = GG(C, D, A, B, X[11], 9);
		B = GG(B, C, D, A, X[15], 13);

		A = HH(A, B, C, D, X[0], 3);
		D = HH(D, A, B, C, X[8], 9);
		C = HH(C, D, A, B, X[4], 11);
		B = HH(B, C, D, A, X[12], 15);
		A = HH(A, B, C, D, X[2], 3);
		D = HH(D, A, B, C, X[10], 9);
		C = HH(C, D, A, B, X[6], 11);
		B = HH(B, C, D, A, X[14], 15);
		A = HH(A, B, C, D, X[1], 3);
		D = HH(D, A, B, C, X[9], 9);
		C = HH(C, D, A, B, X[5], 11);
		B = HH(B, C, D, A, X[13], 15);
		A = HH(A, B, C, D, X[3], 3);
		D = HH(D, A, B, C, X[11], 9);
		C = HH(C, D, A, B, X[7], 11);
		B = HH(B, C, D, A, X[15], 15);

		context[0] += A;
		context[1] += B;
		context[2] += C;
		context[3] += D;
	}

	private int FF(int a, int b, int c, int d, int x, int s) {
		int t = a + ((b & c) | (~b & d)) + x;
		return t << s | t >>> (32 - s);
	}

	private int GG(int a, int b, int c, int d, int x, int s) {
		int t = a + ((b & (c | d)) | (c & d)) + x + 0x5A827999;
		return t << s | t >>> (32 - s);
	}

	private int HH(int a, int b, int c, int d, int x, int s) {
		int t = a + (b ^ c ^ d) + x + 0x6ED9EBA1;
		return t << s | t >>> (32 - s);
	}
}