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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * 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).

 *

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 * 2 along with this work; if not, write to the Free Software Foundation,

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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.

 *

 * @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 encodedKey.length << 3;

    }

}