Implementacja algorytmu DES w języku java

import java.io.*;

class algorithm {
	private byte[] tKey, Msg;
	private byte[][] PKeys;

	public String Run(String mode) {
		return RunDes(mode);
	}

	public String RunDes(String mode) {
		if (Msg.length < 8)
			return "Wiadomość mniejsza od 64 bitów.";
		Msg = selectBits(Msg, IP);
		int blockSize = IP.length;
		byte[] l = selectBits(Msg, 0, blockSize / 2);
		byte[] r = selectBits(Msg, blockSize / 2, blockSize / 2);
		int numOfSubKeys = PKeys.length;
		for (int k = 0; k < numOfSubKeys; k++) {
			byte[] rBackup = r;
			r = selectBits(r, E);
			if (mode.equalsIgnoreCase("szyfruj"))
				r = doXORBytes(r, PKeys[k]);
			else if (mode.equalsIgnoreCase("rozszyfruj"))
				r = doXORBytes(r, PKeys[numOfSubKeys - k - 1]);
			r = substitution6x4(r);
			r = selectBits(r, P);
			r = doXORBytes(l, r);
			l = rBackup;
		}
		byte[] lr = concatenateBits(r, blockSize / 2, l, blockSize / 2);
		lr = selectBits(lr, INVP);

		String ret = "";
		for (int i = 0; i < lr.length; i++) {
			ret = ret + (char) lr[i];
		}
		return ret;
	}

	public void AddKey(String key) {
		try {
			tKey = key.getBytes();
			PKeys = getSubkeys(tKey);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public void AddMsg(String msg) {
		try {
			Msg = msg.getBytes();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	static final int[] IP = { 58, 50, 42, 34, 26, 18, 10, 2, 60, 52, 44, 36, 28, 20, 12, 4, 62, 54, 46, 38, 30, 22, 14, 6, 64, 56, 48, 40, 32, 24, 16, 8, 57, 49, 41, 33, 25, 17, 9, 1, 59, 51, 43, 35,
			27, 19, 11, 3, 61, 53, 45, 37, 29, 21, 13, 5, 63, 55, 47, 39, 31, 23, 15, 7 };
	static final int[] E = { 32, 1, 2, 3, 4, 5, 4, 5, 6, 7, 8, 9, 8, 9, 10, 11, 12, 13, 12, 13, 14, 15, 16, 17, 16, 17, 18, 19, 20, 21, 20, 21, 22, 23, 24, 25, 24, 25, 26, 27, 28, 29, 28, 29, 30, 31,
			32, 1 };
	static final int[] P = { 16, 7, 20, 21, 29, 12, 28, 17, 1, 15, 23, 26, 5, 18, 31, 10, 2, 8, 24, 14, 32, 27, 3, 9, 19, 13, 30, 6, 22, 11, 4, 25 };
	static final int[] INVP = { 40, 8, 48, 16, 56, 24, 64, 32, 39, 7, 47, 15, 55, 23, 63, 31, 38, 6, 46, 14, 54, 22, 62, 30, 37, 5, 45, 13, 53, 21, 61, 29, 36, 4, 44, 12, 52, 20, 60, 28, 35, 3, 43,
			11, 51, 19, 59, 27, 34, 2, 42, 10, 50, 18, 58, 26, 33, 1, 41, 9, 49, 17, 57, 25 };

	private static byte[] doXORBytes(byte[] a, byte[] b) {
		byte[] out = new byte[a.length];
		for (int i = 0; i < a.length; i++) {
			out[i] = (byte) (a[i] ^ b[i]);
		}
		return out;
	}

	static final int[] S = { 14, 4, 13, 1, 2, 15, 11, 8, 3,
			10,
			6,
			12,
			5,
			9,
			0,
			7, // S1
			0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8, 4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0, 15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13, 15, 1, 8, 14, 6, 11, 3,
			4, 9, 7,
			2,
			13,
			12,
			0,
			5,
			10, // S2
			3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5, 0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15, 13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9, 10, 0, 9, 14, 6, 3, 15,
			5, 1, 13, 12,
			7,
			11,
			4,
			2,
			8, // S3
			13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1, 13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7, 1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12, 7, 13, 14, 3, 0, 6, 9,
			10, 1, 2, 8, 5,
			11,
			12,
			4,
			15, // S4
			13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9, 10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4, 3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14, 2, 12, 4, 1, 7, 10, 11,
			6, 8, 5, 3, 15, 13,
			0,
			14,
			9, // S5
			14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6, 4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14, 11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3, 12, 1, 10, 15, 9, 2, 6,
			8, 0, 13, 3, 4, 14, 7,
			5,
			11, // S6
			10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8, 9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6, 4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13, 4, 11, 2, 14, 15, 0, 8,
			13, 3, 12, 9, 7, 5, 10, 6,
			1, // S7
			13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6, 1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2, 6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12, 13, 2, 8, 4, 6, 15, 11,
			1, 10, 9, 3, 14, 5, 0, 12, 7, // S8
			1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2, 7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8, 2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11 };

	private static byte[] substitution6x4(byte[] in) {
		in = splitBytes(in, 6);
		byte[] out = new byte[in.length / 2];
		int lhByte = 0;
		for (int b = 0; b < in.length; b++) {
			byte valByte = in[b];
			int r = 2 * (valByte >> 7 & 0x0001) + (valByte >> 2 & 0x0001);
			int c = valByte >> 3 & 0x000F;
			int hByte = S[64 * b + 16 * r + c];
			if (b % 2 == 0)
				lhByte = hByte;
			else
				out[b / 2] = (byte) (16 * lhByte + hByte);
		}
		return out;
	}

	private static byte[] splitBytes(byte[] in, int len) {
		int numOfBytes = (8 * in.length - 1) / len + 1;
		byte[] out = new byte[numOfBytes];
		for (int i = 0; i < numOfBytes; i++) {
			for (int j = 0; j < len; j++) {
				int val = getBit(in, len * i + j);
				setBit(out, 8 * i + j, val);
			}
		}
		return out;
	}

	static final int[] PC1 = { 57, 49, 41, 33, 25, 17, 9, 1, 58, 50, 42, 34, 26, 18, 10, 2, 59, 51, 43, 35, 27, 19, 11, 3, 60, 52, 44, 36, 63, 55, 47, 39, 31, 23, 15, 7, 62, 54, 46, 38, 30, 22, 14,
			6, 61, 53, 45, 37, 29, 21, 13, 5, 28, 20, 12, 4 };
	static final int[] PC2 = { 14, 17, 11, 24, 1, 5, 3, 28, 15, 6, 21, 10, 23, 19, 12, 4, 26, 8, 16, 7, 27, 20, 13, 2, 41, 52, 31, 37, 47, 55, 30, 40, 51, 45, 33, 48, 44, 49, 39, 56, 34, 53, 46, 42,
			50, 36, 29, 32 };
	static final int[] SHIFTS = { 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 };

	private static byte[][] getSubkeys(byte[] theKey) throws Exception {
		int activeKeySize = PC1.length;
		int numOfSubKeys = SHIFTS.length;
		byte[] activeKey = selectBits(theKey, PC1);
		int halfKeySize = activeKeySize / 2;
		byte[] c = selectBits(activeKey, 0, halfKeySize);
		byte[] d = selectBits(activeKey, halfKeySize, halfKeySize);
		byte[][] subKeys = new byte[numOfSubKeys][];
		for (int k = 0; k < numOfSubKeys; k++) {
			c = rotateLeft(c, halfKeySize, SHIFTS[k]);
			d = rotateLeft(d, halfKeySize, SHIFTS[k]);
			byte[] cd = concatenateBits(c, halfKeySize, d, halfKeySize);
			subKeys[k] = selectBits(cd, PC2);
		}
		return subKeys;
	}

	private static byte[] rotateLeft(byte[] in, int len, int step) {
		int numOfBytes = (len - 1) / 8 + 1;
		byte[] out = new byte[numOfBytes];
		for (int i = 0; i < len; i++) {
			int val = getBit(in, (i + step) % len);
			setBit(out, i, val);
		}
		return out;
	}

	private static byte[] concatenateBits(byte[] a, int aLen, byte[] b, int bLen) {
		int numOfBytes = (aLen + bLen - 1) / 8 + 1;
		byte[] out = new byte[numOfBytes];
		int j = 0;
		for (int i = 0; i < aLen; i++) {
			int val = getBit(a, i);
			setBit(out, j, val);
			j++;
		}
		for (int i = 0; i < bLen; i++) {
			int val = getBit(b, i);
			setBit(out, j, val);
			j++;
		}
		return out;
	}

	private static byte[] selectBits(byte[] in, int pos, int len) {
		int numOfBytes = (len - 1) / 8 + 1;
		byte[] out = new byte[numOfBytes];
		for (int i = 0; i < len; i++) {
			int val = getBit(in, pos + i);
			setBit(out, i, val);
		}
		return out;
	}

	private static byte[] selectBits(byte[] in, int[] map) {
		int numOfBytes = (map.length - 1) / 8 + 1;
		byte[] out = new byte[numOfBytes];
		for (int i = 0; i < map.length; i++) {
			int val = getBit(in, map[i] - 1);
			setBit(out, i, val);
		}
		return out;
	}

	private static int getBit(byte[] data, int pos) {
		int posByte = pos / 8;
		int posBit = pos % 8;
		byte valByte = data[posByte];
		int valInt = valByte >> (8 - (posBit + 1)) & 0x0001;
		return valInt;
	}

	private static void setBit(byte[] data, int pos, int val) {
		int posByte = pos / 8;
		int posBit = pos % 8;
		byte oldByte = data[posByte];
		oldByte = (byte) (((0xFF7F >> posBit) & oldByte) & 0x00FF);
		byte newByte = (byte) ((val << (8 - (posBit + 1))) | oldByte);
		data[posByte] = newByte;
	}

	private String RetBytes(byte[] data, String name) {
		String ret = "";
		for (int i = 0; i < data.length; i++)
			ret += data[i];

		return String.valueOf(ret);
	}

	private static String byteToBits(byte b) {
		StringBuffer buf = new StringBuffer();
		for (int i = 0; i < 8; i++)
			buf.append((int) (b >> (8 - (i + 1)) & 0x0001));
		return buf.toString();
	}
}