Rc4Cipher.java

/*
 * Copyright 2016-2022 chronicle.software
 *
 *       https://chronicle.software
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.openhft.chronicle.salt;

import net.openhft.chronicle.bytes.Bytes;

public class Rc4Cipher {

    private final int[] state;

    private final int[] key;

    public Rc4Cipher(int[] key) {
        state = new int[256];
        this.key = key;
        ksa();
    }

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

    private void ksa() {
        for (int i = 0; i < state.length; i++) {
            state[i] = i;
        }
        int j = 0;
        for (int i = 0; i < state.length; i++) {
            j = (j + state[i] + key[i % key.length]) % 256;
            swap(i, j);
        }
    }

    public void prga(Bytes<?> buffer, long size) {
        int i = 0;
        int j = 0;
        for (int c = 0; c < size; c++) {
            i = (i + 1) % 256;
            j = (j + state[i]) % 256;
            swap(i, j);
            buffer.writeByte((byte) state[(state[i] + state[j]) % 256]);
        }
    }
}