http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5. 
package org.bouncycastle.crypto;


base interface for general purpose byte derivation functions.

/**
 * base interface for general purpose byte derivation functions.
 */
public interface DerivationFunction
{
    public void init(DerivationParameters param);

    
return the message digest used as the basis for the function

/**
     * return the message digest used as the basis for the function
     */
    public Digest getDigest();

    public int generateBytes(byte[] out, int outOff, int len)
        throws DataLengthException, IllegalArgumentException;
}