Java tutorial
/* eMusic/J - a Free software download manager for emusic.com http://www.kallisti.net.nz/emusicj Copyright (C) 2005, 2006 Robin Sheat This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program 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 for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ package nz.net.kallisti.emusicj.metafiles.streams; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.InputStream; import org.apache.commons.codec.binary.Base64; /** * <p>This stream decrypts an eMusic data file.</p> * <p>The algorithm for this was ported directly from the * <a href="http://frumppyoldwoman.com/emusicdlm/decrypt-emp.tar.gz">decrypt-emp</a> * script.</p> * * <p>$Id$</p> * * @author robin */ public class EMPDecoderStream extends InputStream { private InputStream input; // This is the key for decrypting files. private int[] key = { 0x6b, 0xd8, 0x44, 0x87, 0x52, 0x94, 0xfd, 0x6e, 0x2c, 0x18, 0xe4, 0xc8, 0xde, 0x0b, 0xfa, 0x6d, 0xb5, 0x06, 0x7b, 0xce, 0x77, 0xf4, 0x67, 0x3f, 0x93, 0x09, 0x1c, 0x20, 0xf5, 0xbe, 0x27, 0xb1, 0x02, 0xc9, 0x8f, 0x37, 0x68, 0x5e, 0xc1, 0x91, 0xb4, 0x57, 0x8d, 0x90, 0x55, 0x8e, 0x45, 0x19, 0xdb, 0x9c, 0xec, 0xa3, 0x9d, 0x32, 0xf7, 0x81, 0xc5, 0x61, 0x8b, 0xab, 0x30, 0xa0, 0xbc, 0x31, 0xdf, 0xf3, 0x4b, 0xa9, 0x2f, 0x3a, 0x4a, 0xbf, 0x08, 0x66, 0xa7, 0xe2, 0x62, 0x3d, 0x36, 0xb2, 0x4f, 0x73, 0x6c, 0x9a, 0x56, 0xcf, 0x33, 0xe5, 0x43, 0x10, 0x17, 0xc2, 0x3e, 0x1e, 0x2b, 0x70, 0x04, 0x7e, 0xc0, 0x9e, 0xc6, 0x4c, 0x92, 0x5c, 0x0f, 0x23, 0x35, 0xd2, 0x7a, 0x3b, 0xaf, 0x80, 0xd6, 0x9f, 0x0e, 0x78, 0x63, 0x76, 0x95, 0x58, 0x1d, 0x83, 0x22, 0x4d, 0x96, 0xda, 0xc4, 0xae, 0xca, 0xcb, 0xed, 0xd9, 0x86, 0x98, 0xea, 0xef, 0xc3, 0xd0, 0x00, 0xba, 0x71, 0x46, 0xa8, 0x42, 0x72, 0x2a, 0xd1, 0x49, 0xe8, 0xd3, 0xc7, 0xd5, 0x50, 0xcc, 0x47, 0x21, 0xd7, 0x60, 0x38, 0x3c, 0xe7, 0xd4, 0x89, 0xb6, 0x8a, 0x0c, 0xb8, 0xac, 0x0d, 0x82, 0x29, 0x05, 0xe6, 0x5f, 0xfc, 0x5a, 0x12, 0x74, 0x5d, 0x8c, 0x14, 0x03, 0x2d, 0x59, 0x6f, 0xdc, 0x28, 0x7c, 0x15, 0xad, 0xa2, 0x26, 0x11, 0x9b, 0x99, 0x24, 0xfb, 0xf8, 0xa4, 0x07, 0x7d, 0x64, 0x75, 0x1b, 0xcd, 0xa5, 0x25, 0xfe, 0xb7, 0xb9, 0xff, 0x5b, 0xb0, 0xe0, 0x13, 0x51, 0x65, 0x4e, 0xbb, 0xf1, 0xeb, 0x48, 0x39, 0x53, 0xf0, 0xe9, 0x85, 0xf2, 0x69, 0x0a, 0xaa, 0x34, 0x84, 0x40, 0x41, 0x54, 0xdd, 0xf6, 0x1f, 0xbd, 0xa1, 0xe1, 0x1a, 0xe3, 0x01, 0x97, 0x88, 0xa6, 0xf9, 0x2e, 0x16, 0xb3, 0x6a, 0xee, 0x79, 0x7f }; private byte[] decBuffer = null; private int ptr = 0; private int bufferLength; /** * Creates an instance of the stream. Needs to be supplied with an * InputStream that actually reads the data. * @param in the stream that provides the encrypted data */ public EMPDecoderStream(InputStream in) { super(); this.input = in; } /** * Provides a decrypted byte of the file */ @Override public int read() throws IOException { // On the first read, go and decode everything // We use a ByteArrayOutputStream to move everything into a buffer ByteArrayOutputStream bs = new ByteArrayOutputStream(); byte[] buff = new byte[1024]; int count = 0; while ((count = input.read(buff)) != -1) { bs.write(buff, 0, count); } byte[] encoded = bs.toByteArray(); // Now fix the broken Base64 in the file for (int i = 0; i < encoded.length; i++) { switch (encoded[i]) { case '.': { encoded[i] = '+'; break; } case '_': { encoded[i] = '/'; break; } case '-': { encoded[i] = '='; break; } } } byte[] ciphertext; try { ciphertext = Base64.decodeBase64(encoded); } catch (ArrayIndexOutOfBoundsException e) { // Thrown if the decoder gets confused. throw new IOException("Decoding of file stream failed"); } // Now do the decryption int carry = 0; for (int keyIdx = 1; keyIdx < ciphertext.length; ++keyIdx) { int k1 = key[keyIdx & 0xFF]; // update carryover carry += k1; carry &= 0xFF; int k2 = key[carry]; // exchange key bytes key[keyIdx & 0xFF] = k2; key[carry] = k1; ciphertext[keyIdx - 1] ^= key[(k1 + k2) & 0xFF]; decBuffer = ciphertext; bufferLength = decBuffer.length; // For some reason these files seem to have a trailing character, so // we'll go back one step (there seems to always be at least one), then // we'll walk backwards until we see a '>' and set that to the end // of the file bufferLength--; while (bufferLength > 0 && decBuffer[bufferLength - 1] != '>') bufferLength--; } if (ptr >= bufferLength) return -1; return decBuffer[ptr++]; } //TODO make a more efficient version of the above for blocks of bytes }