Class DSSSignature

Implemented Interfaces:
Cloneable, ISignature

public class DSSSignature
extends BaseSignature

The DSS (Digital Signature Standard) algorithm makes use of the following parameters:
  1. p: A prime modulus, where 2L-1 < p < 2L for 512 <= L <= 1024 and L a multiple of 64.
  2. q: A prime divisor of p - 1, where 2159 < q < 2160.
  3. g: Where g = h(p-1)/q mod p, where h is any integer with 1 < h < p - 1 such that h (p-1)/q mod p > 1 (g has order q mod p).
  4. x: A randomly or pseudorandomly generated integer with 0 < x < q.
  5. y: y = gx mod p.
  6. k: A randomly or pseudorandomly generated integer with 0 < k < q.

The integers p, q, and g can be public and can be common to a group of users. A user's private and public keys are x and y, respectively. They are normally fixed for a period of time. Parameters x and k are used for signature generation only, and must be kept secret. Parameter k must be regenerated for each signature.

The signature of a message M is the pair of numbers r and s computed according to the equations below:

In the above, k-1 is the multiplicative inverse of k, mod q; i.e., (k-1 k) mod q = 1 and 0 < k-1 < q. The value of SHA(M) is a 160-bit string output by the Secure Hash Algorithm specified in FIPS 180. For use in computing s, this string must be converted to an integer.

As an option, one may wish to check if r == 0 or s == 0 . If either r == 0 or s == 0, a new value of k should be generated and the signature should be recalculated (it is extremely unlikely that r == 0 or s == 0 if signatures are generated properly).

The signature is transmitted along with the message to the verifier.


  1. Digital Signature Standard (DSS), Federal Information Processing Standards Publication 186. National Institute of Standards and Technology.

Field Summary

Fields inherited from class

md, privateKey, publicKey, schemeName

Fields inherited from interface


Constructor Summary

Trivial 0-arguments constructor.

Method Summary

Returns a clone copy of this instance.
protected Object
protected void
setupForSigning(PrivateKey k)
protected void
setupForVerification(PublicKey k)
static BigInteger[]
sign(DSAPrivateKey k, byte[] h)
static BigInteger[]
sign(DSAPrivateKey k, byte[] h, IRandom irnd)
static BigInteger[]
sign(DSAPrivateKey k, byte[] h, Random rnd)
static boolean
verify(DSAPublicKey k, byte[] h, BigInteger[] rs)
protected boolean
verifySignature(Object sig)

Methods inherited from class

clone, generateSignature, init, name, nextRandomBytes, setupForSigning, setupForVerification, setupSign, setupVerify, sign, update, update, verify, verifySignature

Methods inherited from class java.lang.Object

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

Constructor Details


public DSSSignature()
Trivial 0-arguments constructor.

Method Details


public Object clone()
Returns a clone copy of this instance.
Specified by:
clone in interface ISignature
clone in interface BaseSignature
a clone copy of this instance.


protected Object generateSignature()
            throws IllegalStateException
generateSignature in interface BaseSignature


protected void setupForSigning(PrivateKey k)
            throws IllegalArgumentException
setupForSigning in interface BaseSignature


protected void setupForVerification(PublicKey k)
            throws IllegalArgumentException
setupForVerification in interface BaseSignature


public static final BigInteger[] sign(DSAPrivateKey k,
                                      byte[] h)


public static final BigInteger[] sign(DSAPrivateKey k,
                                      byte[] h,
                                      IRandom irnd)


public static final BigInteger[] sign(DSAPrivateKey k,
                                      byte[] h,
                                      Random rnd)


public static final boolean verify(DSAPublicKey k,
                                   byte[] h,
                                   BigInteger[] rs)


protected boolean verifySignature(Object sig)
            throws IllegalStateException
verifySignature in interface BaseSignature -- 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.