gnu.crypto.sig.dss
Class DSSSignature

java.lang.Object
  gnu.crypto.sig.BaseSignature
      gnu.crypto.sig.dss.DSSSignature

All Implemented Interfaces:

java.lang.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:

• r = (gk mod p) mod q and
• s = (k-1(SHA(M) + xr)) mod q.

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.

References:

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

Version:

$Revision: 1.2 $

Field Summary

Fields inherited from class gnu.crypto.sig.BaseSignature

md, privateKey, publicKey, schemeName

Fields inherited from interface gnu.crypto.sig.ISignature

SIGNER_KEY, SOURCE_OF_RANDOMNESS, VERIFIER_KEY

Constructor Summary

DSSSignature()
Trivial 0-arguments constructor.

Method Summary

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

Methods inherited from class gnu.crypto.sig.BaseSignature

init, name, nextRandomBytes, setupSign, setupVerify, sign, update, update, verify

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DSSSignature

public DSSSignature()

Trivial 0-arguments constructor.

Method Detail

sign

public static final java.math.BigInteger[] sign(java.security.interfaces.DSAPrivateKey k,
                                                byte[] h)

sign

public static final java.math.BigInteger[] sign(java.security.interfaces.DSAPrivateKey k,
                                                byte[] h,
                                                java.util.Random rnd)

sign

public static final java.math.BigInteger[] sign(java.security.interfaces.DSAPrivateKey k,
                                                byte[] h,
                                                IRandom irnd)

verify

public static final boolean verify(java.security.interfaces.DSAPublicKey k,
                                   byte[] h,
                                   java.math.BigInteger[] rs)

clone

public java.lang.Object clone()

Description copied from interface: ISignature

Returns a clone copy of this instance.

Specified by:

clone in interface ISignature

Specified by:

clone in class BaseSignature

setupForVerification

protected void setupForVerification(java.security.PublicKey k)
                             throws java.lang.IllegalArgumentException

Specified by:

setupForVerification in class BaseSignature

Throws:

java.lang.IllegalArgumentException

setupForSigning

protected void setupForSigning(java.security.PrivateKey k)
                        throws java.lang.IllegalArgumentException

Specified by:

setupForSigning in class BaseSignature

Throws:

java.lang.IllegalArgumentException

generateSignature

protected java.lang.Object generateSignature()
                                      throws java.lang.IllegalStateException

Specified by:

generateSignature in class BaseSignature

Throws:

java.lang.IllegalStateException

verifySignature

protected boolean verifySignature(java.lang.Object sig)
                           throws java.lang.IllegalStateException

Specified by:

verifySignature in class BaseSignature

Throws:

java.lang.IllegalStateException