www.pudn.com > encryption.rar > HashOutputStream.java

/*
Christoforos Pirillos @ Villanova University - May 1999
based on code from the book "Java Network Programming" by Hughes
*/

package encryption;
import java.io.*;

/**We attach this to an OutputStream and use a hash function to provide
message integrity and authenticity*/

public class HashOutputStream extends FilterOutputStream {
	
	protected ByteArrayOutputStream byteO;
	protected DataOutputStream dataO;
	protected Hash h;

/**In the constructor we create the ByteArrayOutputStream byteO that will
buffer all of the data that are written to us. We attach a
DataOutputStream dataO to the OutputStream o; we will use this to write
the message and digest*/

public HashOutputStream (OutputStream o, Hash h) {
	super (new ByteArrayOutputStream () );
	byteO = (ByteArrayOutputStream) out;
	dataO = new DataOutputStream (o);
	this.h = h;
}

/**Flush the stream*/

public void flush() throws IOException {
	writeHashed ();
	dataO.flush();
}

/**close the stream*/

public void close () throws IOException {
	flush();
	dataO.close();
}

/**Writes the message and digest to the attached stream dataO*/

protected void writeHashed () throws IOException {
	if (byteO.size () > 0 ) {
		byte[] b = byteO.toByteArray();
		byteO.reset();
		dataO.writeInt (b.length);
		dataO.write(b);
		byte[] hash = h.digest (b);
		dataO.write(hash);
	}
}

} /*end of class HashOutputStream */