Class UHash32

Implemented Interfaces:

public class UHash32
extends BaseMac

UHASH is a keyed hash function, which takes as input a string of arbitrary length, and produces as output a string of fixed length (such as 8 bytes). The actual output length depends on the parameter UMAC-OUTPUT-LEN.

UHASH has been shown to be epsilon-ASU ("Almost Strongly Universal"), where epsilon is a small (parameter-dependent) real number. Informally, saying that a keyed hash function is epsilon-ASU means that for any two distinct fixed input strings, the two outputs of the hash function with a random key "look almost like a pair of random strings". The number epsilon measures how non-random the output strings may be.

UHASH has been designed to be fast by exploiting several architectural features of modern commodity processors. It was specifically designed for use in UMAC. But UHASH is useful beyond that domain, and can be easily adopted for other purposes.

UHASH does its work in three layers. First, a hash function called NH is used to compress input messages into strings which are typically many times smaller than the input message. Second, the compressed message is hashed with an optimized polynomial hash function into a fixed-length 16-byte string. Finally, the 16-byte string is hashed using an inner-product hash into a string of length WORD-LEN bytes. These three layers are repeated (with a modified key) until the outputs total UMAC-OUTPUT-LEN bytes.


  1. UMAC: Message Authentication Code using Universal Hashing.
    T. Krovetz, J. Black, S. Halevi, A. Hevia, H. Krawczyk, and P. Rogaway.

Field Summary

Fields inherited from class gnu.javax.crypto.mac.BaseMac

name, truncatedSize, underlyingHash

Fields inherited from interface gnu.javax.crypto.mac.IMac


Constructor Summary

Trivial 0-arguments constructor.

Method Summary

init(Map<K,V> attributes)
update(byte b)
update(byte[] b, int offset, int len)

Methods inherited from class gnu.javax.crypto.mac.BaseMac

clone, digest, init, macSize, name, reset, selfTest, update, update

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details


public UHash32()
Trivial 0-arguments constructor.

Method Details


public Object clone()
Specified by:
clone in interface IMac
clone in interface BaseMac


public byte[] digest()
Specified by:
digest in interface IMac
digest in interface BaseMac


public void init(Map<K,V> attributes)
            throws InvalidKeyException,
Specified by:
init in interface IMac
init in interface BaseMac


public int macSize()
Specified by:
macSize in interface IMac
macSize in interface BaseMac


public void reset()
Specified by:
reset in interface IMac
reset in interface BaseMac


public boolean selfTest()
Specified by:
selfTest in interface IMac
selfTest in interface BaseMac


public void update(byte b)
Specified by:
update in interface IMac
update in interface BaseMac


public void update(byte[] b,
                   int offset,
                   int len)
Specified by:
update in interface IMac
update in interface BaseMac -- Copyright (C) 2001, 2002, 2003, 2006 Free Software Foundation, Inc. This file is a part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.