Hash function not use MessageDigest

Question

Anyone knows which implementation method of SHA Hash function does not use MessageDigest?
Thanks

Answer 1

If you don't want the MessageDigest interface to a JCE provider, you'll need to reference instead a class based on MessageDigestSPI.
Sun currently allows using directly the "SHA" class in the "sun.java.security" package (as it is based on MessageDigestSPI, you already have a documented API for it:
public class SHA extends MessageDigestSPI
    implements Cloneable {
    public SHA();
    public int engineGetLength(); // returns 20
    public void engineUpdate(byte value);
    public void engineUpdate(byte[] buffer, int offset, int length);
    public byte[] engineDigest() throws java.security.DigestException;
    public void engineReset();
}Also this class implements Clonable, meaning that you can preserve its internal state before calling engineDigest() that will (before returning the final value) reset the internal state and clear the internal "evidence data" in the instance.
To use it:
import java.security.*;
SHA state = new SHA(); // pass argument (0) if you want the deprecated SHA-0 algorithm instead of SHA-1
byte b = ...;
state.engineUpdate(b);
byte[] buffer = ...;
state.engineUpdate(buffer, 0, buffer.length);
byte[] digestBytes = state.engineDigest(); // implicitly calls state.engineReset() before returning