Cryptography Streams: Digest Decryptor, Java example Java code example - Click here to copy ->>>

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/* Title: Hardcore Java
* Title: Java I/O
* Second Edition: May 2006
* ISBN 10: 0-596-52750-0
* ISBN 13: 9780596527501
*/

Code:





import java.io.*;

import java.security.*;

import java.security.spec.*;

import javax.crypto.*;

import javax.crypto.spec.*;



public class DigestDecryptor {



  public static void main(String[] args)

   throws IOException, GeneralSecurityException {



    if (args.length != 3) {

      System.err.println("Usage: java DigestDecryptor infile outfile password");

      return;

    }



    String infile = args[0];

    String outfile = args[1];

    String password = args[2];



    if (password.length() < 8 ) {

      System.err.println("Password must be at least eight characters long");

    }

    

    FileInputStream fin = new FileInputStream(infile);

    FileOutputStream fout = new FileOutputStream(outfile);



    // Get the digest.

    FileInputStream digestIn = new FileInputStream(infile + ".digest");

    DataInputStream dataIn = new DataInputStream(digestIn);

    // SHA digests are always 20 bytes long .

    byte[] oldDigest = new byte[20];

    dataIn.readFully(oldDigest);

    dataIn.close();



    // Create a key.

    byte[] desKeyData = password.getBytes();

    DESKeySpec desKeySpec = new DESKeySpec(desKeyData);

    SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES");

    SecretKey desKey = keyFactory.generateSecret(desKeySpec);



    // Use Data Encryption Standard.

    Cipher des = Cipher.getInstance("DES/ECB/PKCS5Padding");

    des.init(Cipher.DECRYPT_MODE, desKey);

    CipherOutputStream cout = new CipherOutputStream(fout, des);



    // Use SHA digest algorithm.

    MessageDigest sha = MessageDigest.getInstance("SHA");

    DigestInputStream din = new DigestInputStream(fin, sha);



    byte[] input = new byte[64];

    while (true) {

      int bytesRead = din.read(input);

      if (bytesRead == -1) break;

      cout.write(input, 0, bytesRead);

    }

    

    byte[] newDigest = sha.digest();

    if (!MessageDigest.isEqual(newDigest, oldDigest)) {

      System.out.println("Input file appears to be corrupt!");

    }



    din.close();

    cout.flush();

    cout.close();

  }

}