elgamal.c

Implementation Of ELGAMAL Public key encryption in C . it can use very long key os size 2007 decimal

#include<stdio.h>
#include"lip.h"
#include<time.h>


/*public key=(p,g,k);    private key=(p,g,a);*/
long nbtest=120;
void xrand(verylong seed,verylong *b){
	verylong temp=0;
	zintoz((long)69069,b);
	verylong c=0;
	zintoz((long)5,&c);
	zintoz((long)10,&temp);
	verylong min=0;
	verylong max=0;
	int i;
	i=1;
	zsexp(temp,(long)207,&min);
//	zwriteln(min);
	zsexp(temp,(long)208,&max);
	zone(&temp);
//	zwriteln(temp);
	zsub(max,temp,&max);
//	zwriteln(max);
	while(i==1){
	zmul(*b,seed,&temp);
	zadd(temp,c,b);
	i=zcompare(min,*b);
	}
	i=zcompare(max,*b);
	do{
		zsdiv(*b,(long)10,b);
		i=zcompare(max,*b);
	}while(i!=1);
	i=z2mod(*b);
		if(i==0){
			zsadd(*b,1,b);
	}
/*	printf("Seed: ");
	zwriteln(seed);*/
	return ;
}

void xfindprime(verylong *b){
	long i=0;
	verylong add2=0;
	zintoz((long)2,&add2);
	while(i==0){
		zadd(add2,*b,b);
		i=zprobprime(*b,nbtest);
	}
	return ;
}

void encryptMesg(verylong p,verylong g,verylong k, verylong mesg,verylong *gamma,verylong *delta){
	verylong e=0;
	verylong seed=0;
	verylong temp=0;
	zintoz(12345,&seed);
	time_t start;
/*	printf("\nEncrypting message : \n\tEnter seed : ");
	zread(&seed);*/
	time(&start);
	long t=0;
	t=(long)start;
	printf("\nencrypting seed %lu : ",t);
	zintoz(t,&seed);
	zrstart(seed);
	zrandomprime(50,nbtest,&e,zrandomb);
	printf("\ne: ");
	zwriteln(e);
	zexpmod(g,e,p,gamma);
	zexpmod(k,e,p,&temp);
	zmulmod(temp,mesg,p,delta);
}

void decryptMesg(verylong p,verylong g,verylong a,verylong gamma,verylong delta,verylong *text){
	verylong temp=0;
	verylong one=0;
	verylong interm=0;
	zone(&one);
	zsub(p,a,&temp);
	zsub(temp,one,&temp);
	zexpmod(gamma,temp,p,&interm);
	zmulmod(interm,delta,p,text);

}
int main(){
    	verylong seed=0;
	verylong random=0;
	verylong prime=0;
	verylong g=0;
	verylong a=0;
	verylong k=0;
	verylong mesg=0;
	verylong gamma=0;
	verylong delta=0;
	verylong text=0;
	time_t start,end;

	/*generator , g=2; */
	zintoz(2,&g);
	time(&start);
	long t=0;
	t=(long)start;
	printf("\nseed for generating P : %lu ",t);
	zintoz(t,&seed);

	/*Find Random Number*/
	xrand(seed,&random);
	zsadd(random,0,&prime);
	printf("\nRandom Number : ");
	zwriteln(random);

	/*Find prime Number*/
	xfindprime(&prime);
	printf("Prime Number(p): ");
	zwriteln(prime);

	time(&end);
	t=(start-end)*132;
	printf("\nseed for generating g : %lu \n ",t);
	zintoz(t,&seed);
	zrstart(seed);
	zrandomprime(50,nbtest,&g,zrandomb);
	printf("(generator)g: ");
	zwriteln(g);

	/*Find a*/


	time(&end);
	t=(start*end)/10000;
	printf("\nseed for generating a : %lu \n ",t);
	zintoz(t,&seed);
	zrstart(seed);
	zrandomprime(50,nbtest,&a,zrandomb);
	printf("a: ");
	zwriteln(a);

	/*Find K*/
	zexpmod(g,a,prime,&k);
	printf("k: ");
	zwriteln(k);

	/*Input message*/
/*	printf("\nEnter Number :  ");
	zread(&mesg);
	printf("\nU have entered :  ");
	zwrite(mesg);
	encryptMesg(prime,g,k,mesg,&gamma,&delta);
	printf("\n\tgamma    :  ");
	zwrite(gamma);
	printf("\n\tdelta    :  ");
	zwrite(delta);
	decryptMesg(prime,g,a,gamma,delta,&text);
	printf("\n\tPlaintext   : ");
	zwrite(text);
	printf("\n\n");*/
	int select=0;
	while(1){
		printf("\nEnter ur choice : ");
		printf("\n1.Encrypt and decrypt both (1) : ");
		printf("\n2.Encrypt only (2) : ");
		printf("\n3.Decrypt only (3) : ");
		printf("\n4.exit(4)	     : ");
		scanf("%d",&select);
		switch(select){
			case 1:
				printf("\nEnter Number :  ");
				zread(&mesg);
				printf("\nU have entered :  ");
				zwrite(mesg);
				encryptMesg(prime,g,k,mesg,&gamma,&delta);
				printf("\n\tgamma    :  ");
				zwrite(gamma);
				printf("\n\tdelta    :  ");
				zwrite(delta);
				decryptMesg(prime,g,a,gamma,delta,&text);
				printf("\n\tPlaintext   : ");
				zwrite(text);
				printf("\n\n");
				break;
			case 2 :
				printf("\nEnter Number :  ");
				zread(&mesg);
				printf("\nU have entered :  ");
				zwrite(mesg);
				encryptMesg(prime,g,k,mesg,&gamma,&delta);
				printf("\n\tgamma    :  ");
				zwrite(gamma);
				printf("\n\tdelta    :  ");
				zwrite(delta);
				printf("\n\n");
				break;
			case 3:
				printf("Enter gamma : ");
				zread(&gamma);
				printf("Enter delta : ");
				zread(&delta);
				decryptMesg(prime,g,a,gamma,delta,&text);
				printf("\n\tPlaintext   : ");
				zwrite(text);
				printf("\n\n");
				break;
			case 4:
				printf("\n\n");
				return 0;
			default:
				printf("Please enter correct option.");
		}
	}
		
	return 0;
}