Extract.java

import java.io.*;
import crypt.*;
import ortega.*;

public class Extract {
    private static File f;	    // carrier file
    private static byte[] carrier;  // carrier data
    private static int[] coeff;     // dct values
    private static FileOutputStream fos;   // embedded file (output file)
    private static String embFileName;	// output file name
    private static String password;

    private static byte[] deZigZag = {
       0,  1,  5,  6, 14, 15, 27, 28,
       2,  4,  7, 13, 16, 26, 29, 42,
       3,  8, 12, 17, 25, 30, 41, 43,
       9, 11, 18, 24, 31, 40, 44, 53,
      10, 19, 23, 32, 39, 45, 52, 54,
      20, 22, 33, 38, 46, 51, 55, 60,
      21, 34, 37, 47, 50, 56, 59, 61,
      35, 36, 48, 49, 57, 58, 62, 63
    };

    static void usage() {
	System.out.println("java Extract [Options] \"image.jpg\"");
	System.out.println("Options:");
	System.out.println("\t-p password (default: abc123)");
	System.out.println("\t-e extractedFileName (default: output.txt)");
        System.out.println("\nAuthor: Andreas Westfeld, westfeld@inf.tu-dresden.de");
	System.exit(0);
    }

    public static void main(String[] args) {
    	embFileName = "output.txt";
	password = "abc123";
	try {
	    if (args.length < 1)
		usage();
	    for (int i=0; i<args.length; i++) {
		if (!args[i].startsWith("-")) {
		    if (!args[i].endsWith(".jpg"))
			usage();
		    f = new File(args[i]);
		    continue;
		}
		if (args.length < i+1) {
		    System.out.println("Missing parameter for switch "+args[i]);
		    usage();
		}
		if (args[i].equals("-e")) {
		    embFileName = args[i+1];
		} else if (args[i].equals("-p")) {
		    password = args[i+1];
		} else
		    System.out.println("Unknown switch "
					    +args[i]+" ignored.");
		i++;
	    }
	    carrier = new byte[(int)f.length()];
	    FileInputStream fis = new FileInputStream(f);
	    fos = new FileOutputStream(new File(embFileName));
	    fis.read(carrier);
	    HuffmanDecode hd = new HuffmanDecode(carrier);
System.out.println("Huffman decoding starts");
	    coeff=hd.decode();
System.out.println("Permutation starts");
	    F5Random random = new F5Random(password.getBytes());
	    Permutation permutation = new Permutation(coeff.length, random);
System.out.println(coeff.length+" indices shuffled");
	    int extractedByte=0;
	    int availableExtractedBits=0;
	    int extractedFileLength=0;
	    int nBytesExtracted=0;
	    int shuffledIndex=0;
	    int extractedBit;
	    int i;
System.out.println("Extraction starts");
	    // extract length information
	    for (i=0; availableExtractedBits<32; i++) {
		shuffledIndex = permutation.getShuffled(i);
		if (shuffledIndex%64 == 0) continue; // skip DC coefficients
		shuffledIndex = shuffledIndex-(shuffledIndex%64)+deZigZag[shuffledIndex%64];
                if (coeff[shuffledIndex] == 0) continue; // skip zeroes
		if (coeff[shuffledIndex] > 0)
		    extractedBit=coeff[shuffledIndex]&1;
		else
		    extractedBit=1-(coeff[shuffledIndex]&1);
		extractedFileLength |= extractedBit << availableExtractedBits++;
	    }
	    // remove pseudo random pad
	    extractedFileLength ^= random.getNextByte();
	    extractedFileLength ^= random.getNextByte()<<8;
	    extractedFileLength ^= random.getNextByte()<<16;
	    extractedFileLength ^= random.getNextByte()<<24;
	    int k = extractedFileLength >> 24;
	    k %= 32;
	    int n = (1 << k)-1;
	    extractedFileLength &= 0x007fffff;
System.out.println("Length of embedded file: "+extractedFileLength+" bytes");
	    availableExtractedBits = 0;
	    if (n>0) {
		int startOfN = i;
		int hash;
		System.out.println("(1, "+n+", "+k+") code used");
extractingLoop:
		do {
		    // 1. read n places, and calculate k bits
		    hash = 0;
		    int code = 1;
		    for (i=0; code<=n; i++) {
			// check for pending end of coeff
			if (startOfN+i>=coeff.length) break extractingLoop;
			shuffledIndex = permutation.getShuffled(startOfN+i);
			if (shuffledIndex%64 == 0) continue; // skip DC coefficients
			shuffledIndex = shuffledIndex-(shuffledIndex%64)+deZigZag[shuffledIndex%64];
			if (coeff[shuffledIndex] == 0) continue; // skip zeroes
			if (coeff[shuffledIndex] > 0)
			    extractedBit=coeff[shuffledIndex]&1;
			else
			    extractedBit=1-(coeff[shuffledIndex]&1);
			if (extractedBit==1) {
			    hash ^= code;
			}
			code++;
		    }
		    startOfN += i;
		    // 2. write k bits bytewise
		    for (i=0; i<k; i++) {
			extractedByte |= ((hash>>i)&1) << availableExtractedBits++;
			if (availableExtractedBits == 8) {
			    // remove pseudo random pad
			    extractedByte ^= random.getNextByte();
			    fos.write((byte) extractedByte);
			    extractedByte=0;
			    availableExtractedBits=0;
			    nBytesExtracted++;
			    // check for pending end of embedded data
			    if (nBytesExtracted==extractedFileLength)
				break extractingLoop;
			}
		    }
		} while (true);
	    } else {
		System.out.println("Default code used");
		for (; i<coeff.length; i++) {
		    shuffledIndex = permutation.getShuffled(i);
		    if (shuffledIndex%64 == 0) continue; // skip DC coefficients
		    shuffledIndex = shuffledIndex-(shuffledIndex%64)+deZigZag[shuffledIndex%64];
		    if (coeff[shuffledIndex] == 0) continue; // skip zeroes
		    if (coeff[shuffledIndex] > 0)
			extractedBit=coeff[shuffledIndex]&1;
		    else
			extractedBit=1-(coeff[shuffledIndex]&1);
		    extractedByte |= extractedBit << availableExtractedBits++;
		    if (availableExtractedBits == 8) {
			// remove pseudo random pad
			extractedByte ^= random.getNextByte();
			fos.write((byte) extractedByte);
			extractedByte=0;
			availableExtractedBits=0;
			nBytesExtracted++;
			if (nBytesExtracted==extractedFileLength)
			    break;
		    }
		}
	    }
	    if (nBytesExtracted<extractedFileLength) {
		System.out.println("Incomplete file: only "+
		    nBytesExtracted+" of "+extractedFileLength+
		    " bytes extracted");
	    }
	} catch(Exception e) {
	    e.printStackTrace();
	}
    }
}