/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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
*
* http://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 org.apache.pdfbox.pdmodel.encryption;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
/**
* An implementation of the RC4 stream cipher.
*
* @author Ben Litchfield
*/
class RC4Cipher
{
private final int[] salt;
private int b;
private int c;
/**
* Constructor.
*/
RC4Cipher()
{
salt = new int[256];
}
/**
* This will reset the key to be used.
*
* @param key The RC4 key used during encryption.
*/
public void setKey( byte[] key )
{
b = 0;
c = 0;
if(key.length < 1 || key.length > 32)
{
throw new IllegalArgumentException("number of bytes must be between 1 and 32");
}
for(int i = 0; i < salt.length; i++)
{
salt[i] = i;
}
int keyIndex = 0;
int saltIndex = 0;
for( int i = 0; i < salt.length; i++)
{
saltIndex = (fixByte(key[keyIndex]) + salt[i] + saltIndex) % 256;
swap( salt, i, saltIndex );
keyIndex = (keyIndex + 1) % key.length;
}
}
/**
* Thie will ensure that the value for a byte >=0.
*
* @param aByte The byte to test against.
*
* @return A value >=0 and < 256
*/
private static int fixByte( byte aByte )
{
return aByte < 0 ? 256 + aByte : aByte;
}
/**
* This will swap two values in an array.
*
* @param data The array to swap from.
* @param firstIndex The index of the first element to swap.
* @param secondIndex The index of the second element to swap.
*/
private static void swap( int[] data, int firstIndex, int secondIndex )
{
int tmp = data[ firstIndex ];
data[ firstIndex ] = data[ secondIndex ];
data[ secondIndex ] = tmp;
}
/**
* This will encrypt and write the next byte.
*
* @param aByte The byte to encrypt.
* @param output The stream to write to.
*
* @throws IOException If there is an error writing to the output stream.
*/
public void write( byte aByte, OutputStream output ) throws IOException
{
b = (b + 1) % 256;
c = (salt[b] + c) % 256;
swap( salt, b, c );
int saltIndex = (salt[b] + salt[c]) % 256;
output.write(aByte ^ (byte)salt[saltIndex]);
}
/**
* This will encrypt and write the data.
*
* @param data The data to encrypt.
* @param output The stream to write to.
*
* @throws IOException If there is an error writing to the output stream.
*/
public void write( byte[] data, OutputStream output ) throws IOException
{
for (byte aData : data)
{
write(aData, output);
}
}
/**
* This will encrypt and write the data.
*
* @param data The data to encrypt.
* @param output The stream to write to.
*
* @throws IOException If there is an error writing to the output stream.
*/
public void write( InputStream data, OutputStream output ) throws IOException
{
byte[] buffer = new byte[1024];
int amountRead;
while( (amountRead = data.read( buffer )) != -1 )
{
write( buffer, 0, amountRead, output );
}
}
/**
* This will encrypt and write the data.
*
* @param data The data to encrypt.
* @param offset The offset into the array to start reading data from.
* @param len The number of bytes to attempt to read.
* @param output The stream to write to.
*
* @throws IOException If there is an error writing to the output stream.
*/
public void write( byte[] data, int offset, int len, OutputStream output) throws IOException
{
for( int i = offset; i < offset + len; i++ )
{
write( data[i], output );
}
}
}