El Gamal Algorithm and Java problem

Reposting your code with markup. In future please use [code] tags, as you can see the effect it has on legibility: import java.math.BigInteger;

import java.math.*;

import java.util.*;

class ElGamel

{

public static void main(String[] args)

{

BigInteger p = new BigInteger("7747");

BigInteger q = new BigInteger("3853");

BigInteger a = new BigInteger("773");

BigInteger k = new BigInteger("1193");

BigInteger msg = new BigInteger("39");

BigInteger y = new BigInteger("0");

BigInteger x = new BigInteger("0");

BigInteger z = new BigInteger("0");

BigInteger temp = new BigInteger("0");

BigInteger t2 = new BigInteger("0");

int t1 = 0;

y = q.modPow(a,p);

System.out.println("Y is "+y);

x = q.modPow(k,p);

System.out.println("X is "+x);

t1 = k.intValue();

z = (msg.multiply(y.pow(t1))).mod(p);

System.out.println("Z is "+z);

t1 = a.intValue();

x = x.pow(t1);

temp = x.modInverse(p);

msg = z.multiply(temp);

System.out.println("Message is "+msg);

}

}

YAT_Archivista at 2007-7-16 0:52:29 >

Now, if you're going to use ints you should use ints, and if you're going to use BigIntegers you should use BigIntegers. One final substitution to your original code: import java.math.BigInteger;

class ElGamal

{

public static void main(String[] args)

{

BigInteger p = new BigInteger("7747");

BigInteger q = new BigInteger("3853");

BigInteger a = new BigInteger("773");

BigInteger k = new BigInteger("1193");

BigInteger msg = new BigInteger("39");

BigInteger y = q.modPow(a,p);

System.out.println("Y is "+y);

BigInteger x = q.modPow(k,p);

System.out.println("X is "+x);

BigInteger z = (msg.multiply(y.modPow(k, p))).mod(p);

System.out.println("Z is "+z);

x = x.modPow(a, p);

BigInteger temp = x.modInverse(p);

msg = z.multiply(temp);

System.out.println("Message is "+msg);

}

}

There's one line in there which doesn't contain the magic three characters "mod". Add a .mod(p) to it and you get the right output.

YAT_Archivista at 2007-7-16 0:52:29 >