RC4.java

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package org.redPandaLib.crypt;

/**
 *
 * @author rflohr
 */
public class RC4 {

    private byte[] key;
    private int[] sbox;
    private static final int SBOX_LENGTH = 256;
    private static final int KEY_MIN_LENGTH = 5;
    private int i = 0;
    private int j = 0;

    public static void main(String[] args) {

        RC4 rce = new RC4(Utils.parseAsHexOrBase58("a0a0a0a0a0"));
        byte[] result = rce.encrypt("hello there".getBytes());
        //System.out.println("encrypted string:\n" + Utils.bytesToHexString(result));

//        byte[] result4 = rce.encrypt("hello there".getBytes());
//        System.out.println("encrypted string:\n" + Utils.bytesToHexString(result) + Utils.bytesToHexString(result4));
//
//
//
//        RC4 rc2 = new RC4("testkey".getBytes());
//        byte[] result2 = rc2.encrypt("hello therehello there".getBytes());
//        System.out.println("encrypted string:\n" + Utils.bytesToHexString(result2));
        RC4 rcd = new RC4(Utils.parseAsHexOrBase58("a0a0a0a0a0"));

        System.out.println("decrypted string:\n"
                + new String(rcd.decrypt(result)));

    }

    public RC4(byte[] key) {

        if (!(key.length >= KEY_MIN_LENGTH && key.length < SBOX_LENGTH)) {
            System.out.println("Key length has to be between "
                    + KEY_MIN_LENGTH + " and " + (SBOX_LENGTH - 1));
        }

        sbox = initSBox(key);
    }

    public RC4() {
    }

    public byte[] decrypt(final byte[] msg) {
        return encrypt(msg);
    }

    public byte[] encrypt(final byte[] msg) {
        byte[] code = new byte[msg.length];
        for (int n = 0; n < msg.length; n++) {
            i = (i + 1) % SBOX_LENGTH;
            j = (j + sbox[i]) % SBOX_LENGTH;
            swap(i, j, sbox);
            int rand = sbox[(sbox[i] + sbox[j]) % SBOX_LENGTH];
            code[n] = (byte) (rand ^ (int) msg[n]);
            //code[n] = (byte) ((rand ^ (int) msg[n]) +SBOX_LENGTH % SBOX_LENGTH);
            //System.out.println("Byte: " + msg[n] + " " + code[n]);

        }
        return code;
    }

    private int[] initSBox(byte[] key) {
        int[] sbox = new int[SBOX_LENGTH];
        int j = 0;

        for (int i = 0; i < SBOX_LENGTH; i++) {
            sbox[i] = i;
        }

        for (int i = 0; i < SBOX_LENGTH; i++) {
            j = (j + sbox[i] + key[i % key.length] + SBOX_LENGTH) % SBOX_LENGTH;
            swap(i, j, sbox);
        }
        return sbox;
    }

    private void swap(int i, int j, int[] sbox) {
        int temp = sbox[i];
        sbox[i] = sbox[j];
        sbox[j] = temp;
    }
}