C Crypt Interoperate with Java Crypt

tooj

There are many open source today.  this also works for the crypt projects.
Yet the  different crypt implementation have some compatibility issue between them.
1. Different implementations
C Crypt implementation
http://www.libtomcrypt.org/
Sun Crypt implematation:
http://java.sun.com
Bouncy Castle Crypt implematation:
http://www.bouncycastle.org/

2. Compatibilty issue.
[color="#800080"]libtomcrypt generate DSA key format can not be supported by java DSA implemation.
[color="#800080"]while bouncycastle do.
[color="#800080"]3. Implementation code.
import java.math.*;
import org.bouncycastle.crypto.params.*;
import org.bouncycastle.crypto.signers.DSASigner;
import org.bouncycastle.crypto.digests.SHA1Digest;
public class SignatureVerifier
{
   private DSASigner dsaSigner = null;

   /** Build Public Key object from the y/p/q/g data files */
   public SignatureVerifier()
      throws FileNotFoundException, IOException
   {
      // Load key parameters from data files
      BigInteger y = readBigInt("y.dat");
      BigInteger p = readBigInt("p.dat");
      BigInteger q = readBigInt("q.dat");
      BigInteger g = readBigInt("g.dat");
     System.out.println( "Y: " + y + "
P: " + p + "
Q: " + q + "
G: " + g);
      DSAParameters dsaParams = new DSAParameters( p, q, g);
      DSAPublicKeyParameters dsaPubParams = new DSAPublicKeyParameters( y, dsaParams );
      dsaSigner = new DSASigner();
      dsaSigner.init( false, dsaPubParams );
   }
   /** Verify the header data
       headerData should be
   */
   public boolean verify( byte[] headerData, byte[] signature )
   {
      boolean valid = false;
      // Build SHA1 digest from the passed in header data
      SHA1Digest sha1 = new SHA1Digest();
      sha1.update( headerData, 0, headerData.length );
            
      byte[] sha1hash = new byte[ sha1.getDigestSize() ];
      sha1.doFinal( sha1hash, 0 );
      // Decompose signature into the r and s values
      byte[] rBytes = new byte[20];
      byte[] sBytes = new byte[20];
      System.arraycopy( signature, 0, rBytes, 0, 20);
      System.arraycopy( signature, 20, sBytes, 0, 20);
      BigInteger r = new BigInteger( 1, rBytes );
      BigInteger s = new BigInteger( 1, sBytes );
      valid = dsaSigner.verifySignature( sha1hash, r, s );
      return(valid);
   }
   /** Reads a BigInteger from a binary file */
   static public BigInteger readBigInt( String filename )  
          throws FileNotFoundException, IOException
   {
       FileInputStream intFIS = new FileInputStream( filename );
       int numBytes = intFIS.available();
       byte[] fileBytes = new byte[numBytes];
       intFIS.read( fileBytes );
       intFIS.close();
       BigInteger bigInt = new BigInteger( 1, fileBytes );
       return(bigInt);
   }
   public static void main( String args[])
   throws Exception
   {
       SignatureVerifier sigVerify = new SignatureVerifier();
    try{
            // Read signature from test file
            byte[] signature =  new byte[40];
            FileInputStream fis = new FileInputStream( "test.txt.sig" );
            fis.read(signature );
            fis.close();
            // Read content file (simulated header)
            byte[] header = new byte[140];
            fis = new FileInputStream( "test.txt" );
            fis.read( header );
            fis.close();
         
                       boolean sigOkay = sigVerify.verify( header, signature );
            System.out.println("signatureOkay=" + sigOkay );
           }catch(Exception e){
               e.printStackTrace();
        }
   }
}


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