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gnu.java.security.sig.dss
Class DSSSignature  

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

All Implemented Interfaces:

java.lang.Cloneable, gnu.java.security.sig.ISignature

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public class DSSSignature

extends gnu.java.security.sig.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.

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Field Summary

 

Fields inherited from class gnu.java.security.sig.BaseSignature

md, privateKey, publicKey, schemeName

 

Fields inherited from interface gnu.java.security.sig.ISignature

SIGNER_KEY, SOURCE_OF_RANDOMNESS, VERIFIER_KEY

 

Constructor Summary
	DSSSignature()           Trivial 0-arguments constructor.
private	DSSSignature(DSSSignature that)           Private constructor for cloning purposes.

 

Method Summary
private  boolean	checkRS(java.math.BigInteger[] rs, byte[] digestBytes)
java.lang.Object	clone()           Returns a clone copy of this instance.
private  java.math.BigInteger[]	computeRS(byte[] digestBytes)
private  java.math.BigInteger[]	decodeSignature(java.lang.Object signature)           Returns the output of a previously generated signature object as a pair of java.math.BigInteger.
private  java.lang.Object	encodeSignature(java.math.BigInteger r, java.math.BigInteger s)           Returns the output of a signature generation phase.
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, gnu.java.security.prng.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.java.security.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.

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DSSSignature

private DSSSignature(DSSSignature that)

Private constructor for cloning purposes.

Method Detail

sign

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

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sign

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

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sign

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

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verify

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

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clone

public java.lang.Object clone()

Description copied from interface: gnu.java.security.sig.ISignature

Returns a clone copy of this instance.

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setupForVerification

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

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setupForSigning

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

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generateSignature

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

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verifySignature

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

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encodeSignature

private java.lang.Object encodeSignature(java.math.BigInteger r,
                                         java.math.BigInteger s)

Returns the output of a signature generation phase.

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decodeSignature

private java.math.BigInteger[] decodeSignature(java.lang.Object signature)

Returns the output of a previously generated signature object as a pair of java.math.BigInteger.

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computeRS

private java.math.BigInteger[] computeRS(byte[] digestBytes)

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checkRS

private boolean checkRS(java.math.BigInteger[] rs,
                        byte[] digestBytes)

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Overview  Package   Class  Use  Deprecated  Index
Home >> All >> gnu >> java >> security >> sig >> [ dss overview ]	PREV CLASS  NEXT CLASS
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

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