/*
 * Copyright (c) 2003, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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 General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.crypto.provider;

import java.security.*;
import java.security.spec.AlgorithmParameterSpec;

import javax.crypto.*;

Implementation of the ARCFOUR cipher, an algorithm apparently compatible
with RSA Security's RC4(tm) cipher. The description of this algorithm was
taken from Bruce Schneier's book Applied Cryptography, 2nd ed.,
section 17.1.
We support keys from 40 to 1024 bits. ARCFOUR would allow for keys shorter
than 40 bits, but that is too insecure for us to permit.
Note that we subclass CipherSpi directly and do not use the CipherCore
framework. That was designed to simplify implementation of block ciphers
and does not offer any advantages for stream ciphers such as ARCFOUR.
Author:
 Andreas Sterbenz
Since:
  1.5/**
 * Implementation of the ARCFOUR cipher, an algorithm apparently compatible
 * with RSA Security's RC4(tm) cipher. The description of this algorithm was
 * taken from Bruce Schneier's book Applied Cryptography, 2nd ed.,
 * section 17.1.
 *
 * We support keys from 40 to 1024 bits. ARCFOUR would allow for keys shorter
 * than 40 bits, but that is too insecure for us to permit.
 *
 * Note that we subclass CipherSpi directly and do not use the CipherCore
 * framework. That was designed to simplify implementation of block ciphers
 * and does not offer any advantages for stream ciphers such as ARCFOUR.
 *
 * @since   1.5
 * @author  Andreas Sterbenz
 */
public final class ARCFOURCipher extends CipherSpi {

    // state array S, 256 entries. The entries are 8-bit, but we use an int[]
    // because int arithmetic is much faster than in Java than bytes.
    private final int[] S;

    // state indices i and j. Called is and js to avoid collision with
    // local variables. 'is' is set to -1 after a call to doFinal()
    private int is, js;

    // the bytes of the last key used (if any)
    // we need this to re-initialize after a call to doFinal()
    private byte[] lastKey;

    // called by the JCE framework
    public ARCFOURCipher() {
        S = new int[256];
    }

    // core key setup code. initializes S, is, and js
    // assumes key is non-null and between 40 and 1024 bit
    private void init(byte[] key) {
        // initialize S[i] to i
        for (int i = 0; i < 256; i++) {
            S[i] = i;
        }

        // we avoid expanding key to 256 bytes and instead keep a separate
        // counter ki = i mod key.length.
        for (int i = 0, j = 0, ki = 0; i < 256; i++) {
            int Si = S[i];
            j = (j + Si + key[ki]) & 0xff;
            S[i] = S[j];
            S[j] = Si;
            ki++;
            if (ki == key.length) {
                ki = 0;
            }
        }

        // set indices to 0
        is = 0;
        js = 0;
    }

    // core crypt code. OFB style, so works for both encryption and decryption
    private void crypt(byte[] in, int inOfs, int inLen, byte[] out,
            int outOfs) {
        if (is < 0) {
            // doFinal() was called, need to reset the cipher to initial state
            init(lastKey);
        }
        while (inLen-- > 0) {
            is = (is + 1) & 0xff;
            int Si = S[is];
            js = (js + Si) & 0xff;
            int Sj = S[js];
            S[is] = Sj;
            S[js] = Si;
            out[outOfs++] = (byte)(in[inOfs++] ^ S[(Si + Sj) & 0xff]);
        }
    }

    // Modes do not make sense with stream ciphers, but allow ECB
    // see JCE spec.
    protected void engineSetMode(String mode) throws NoSuchAlgorithmException {
        if (mode.equalsIgnoreCase("ECB") == false) {
            throw new NoSuchAlgorithmException("Unsupported mode " + mode);
        }
    }

    // Padding does not make sense with stream ciphers, but allow NoPadding
    // see JCE spec.
    protected void engineSetPadding(String padding)
            throws NoSuchPaddingException {
        if (padding.equalsIgnoreCase("NoPadding") == false) {
            throw new NoSuchPaddingException("Padding must be NoPadding");
        }
    }

    // Return 0 to indicate stream cipher
    // see JCE spec.
    protected int engineGetBlockSize() {
        return 0;
    }

    // output length is always the same as input length
    // see JCE spec
    protected int engineGetOutputSize(int inputLen) {
        return inputLen;
    }

    // no IV, return null
    // see JCE spec
    protected byte[] engineGetIV() {
        return null;
    }

    // no parameters
    // see JCE spec
    protected AlgorithmParameters engineGetParameters() {
        return null;
    }

    // see JCE spec
    protected void engineInit(int opmode, Key key, SecureRandom random)
            throws InvalidKeyException {
        init(opmode, key);
    }

    // see JCE spec
    protected void engineInit(int opmode, Key key,
            AlgorithmParameterSpec params, SecureRandom random)
            throws InvalidKeyException, InvalidAlgorithmParameterException {
        if (params != null) {
            throw new InvalidAlgorithmParameterException
                ("Parameters not supported");
        }
        init(opmode, key);
    }

    // see JCE spec
    protected void engineInit(int opmode, Key key,
            AlgorithmParameters params, SecureRandom random)
            throws InvalidKeyException, InvalidAlgorithmParameterException {
        if (params != null) {
            throw new InvalidAlgorithmParameterException
                ("Parameters not supported");
        }
        init(opmode, key);
    }

    // init method. Check opmode and key, then call init(byte[]).
    private void init(int opmode, Key key) throws InvalidKeyException {
        if ((opmode < Cipher.ENCRYPT_MODE) || (opmode > Cipher.UNWRAP_MODE)) {
            throw new InvalidKeyException("Unknown opmode: " + opmode);
        }
        lastKey = getEncodedKey(key);
        init(lastKey);
    }

    // return the encoding of key if key is a valid ARCFOUR key.
    // otherwise, throw an InvalidKeyException
    private static byte[] getEncodedKey(Key key) throws InvalidKeyException {
        String keyAlg = key.getAlgorithm();
        if (!keyAlg.equals("RC4") && !keyAlg.equals("ARCFOUR")) {
            throw new InvalidKeyException("Not an ARCFOUR key: " + keyAlg);
        }
        if ("RAW".equals(key.getFormat()) == false) {
            throw new InvalidKeyException("Key encoding format must be RAW");
        }
        byte[] encodedKey = key.getEncoded();
        if ((encodedKey.length < 5) || (encodedKey.length > 128)) {
            throw new InvalidKeyException
                ("Key length must be between 40 and 1024 bit");
        }
        return encodedKey;
    }

    // see JCE spec
    protected byte[] engineUpdate(byte[] in, int inOfs, int inLen) {
        byte[] out = new byte[inLen];
        crypt(in, inOfs, inLen, out, 0);
        return out;
    }

    // see JCE spec
    protected int engineUpdate(byte[] in, int inOfs, int inLen,
            byte[] out, int outOfs) throws ShortBufferException {
        if (out.length - outOfs < inLen) {
            throw new ShortBufferException("Output buffer too small");
        }
        crypt(in, inOfs, inLen, out, outOfs);
        return inLen;
    }

    // see JCE spec
    protected byte[] engineDoFinal(byte[] in, int inOfs, int inLen) {
        byte[] out = engineUpdate(in, inOfs, inLen);
        is = -1;
        return out;
    }

    // see JCE spec
    protected int engineDoFinal(byte[] in, int inOfs, int inLen,
            byte[] out, int outOfs) throws ShortBufferException {
        int outLen = engineUpdate(in, inOfs, inLen, out, outOfs);
        is = -1;
        return outLen;
    }

    // see JCE spec
    protected byte[] engineWrap(Key key) throws IllegalBlockSizeException,
            InvalidKeyException {
        byte[] encoded = key.getEncoded();
        if ((encoded == null) || (encoded.length == 0)) {
            throw new InvalidKeyException("Could not obtain encoded key");
        }
        return engineDoFinal(encoded, 0, encoded.length);
    }

    // see JCE spec
    protected Key engineUnwrap(byte[] wrappedKey, String algorithm,
            int type) throws InvalidKeyException, NoSuchAlgorithmException {
        byte[] encoded = engineDoFinal(wrappedKey, 0, wrappedKey.length);
        return ConstructKeys.constructKey(encoded, algorithm, type);
    }

    // see JCE spec
    protected int engineGetKeySize(Key key) throws InvalidKeyException {
        byte[] encodedKey = getEncodedKey(key);
        return CipherCore.multiplyExact(encodedKey.length, 8);
    }

}