C code to implement RSA Algorithm(Encryption and Decryption)

RSA Program Input

ENTER FIRST PRIME NUMBER
7

ENTER ANOTHER PRIME NUMBER
17

ENTER MESSAGE
hello

C Program

#include<stdio.h>

#include<conio.h>

#include<stdlib.h>

#include<math.h>

#include<string.h>

long int p,q,n,t,flag,e[100],d[100],temp[100],j,m[100],en[100],i;

char msg[100];

int prime(long int);

void ce();

long int cd(long int);

void encrypt();

void decrypt();

void main() {

	clrscr();

	printf("\nENTER FIRST PRIME NUMBER\n");

	scanf("%d",&p);

	flag=prime(p);

	if(flag==0) {

		printf("\nWRONG INPUT\n");

		getch();

		exit(1);

	}

	printf("\nENTER ANOTHER PRIME NUMBER\n");

	scanf("%d",&q);

	flag=prime(q);

	if(flag==0||p==q) {

		printf("\nWRONG INPUT\n");

		getch();

		exit(1);

	}

	printf("\nENTER MESSAGE\n");

	fflush(stdin);

	scanf("%s",msg);

	for (i=0;msg[i]!=NULL;i++)

	m[i]=msg[i];

	n=p*q;

	t=(p-1)*(q-1);

	ce();

	printf("\nPOSSIBLE VALUES OF e AND d ARE\n");

	for (i=0;i<j-1;i++)

	printf("\n%ld\t%ld",e[i],d[i]);

	encrypt();

	decrypt();

	getch();

}

int prime(long int pr) {

	int i;

	j=sqrt(pr);

	for (i=2;i<=j;i++) {

		if(pr%i==0)

		    return 0;

	}

	return 1;

}

void ce() {

	int k;

	k=0;

	for (i=2;i<t;i++) {

		if(t%i==0)

		    continue;

		flag=prime(i);

		if(flag==1&&i!=p&&i!=q) {

			e[k]=i;

			flag=cd(e[k]);

			if(flag>0) {

				d[k]=flag;

				k++;

			}

			if(k==99)

			        break;

		}

	}

}

long int cd(long int x) {

	long int k=1;

	while(1) {

		k=k+t;

		if(k%x==0)

		    return(k/x);

	}

}

void encrypt() {

	long int pt,ct,key=e[0],k,len;

	i=0;

	len=strlen(msg);

	while(i!=len) {

		pt=m[i];

		pt=pt-96;

		k=1;

		for (j=0;j<key;j++) {

			k=k*pt;

			k=k%n;

		}

		temp[i]=k;

		ct=k+96;

		en[i]=ct;

		i++;

	}

	en[i]=-1;

	printf("\nTHE ENCRYPTED MESSAGE IS\n");

	for (i=0;en[i]!=-1;i++)

	printf("%c",en[i]);

}

void decrypt() {

	long int pt,ct,key=d[0],k;

	i=0;

	while(en[i]!=-1) {

		ct=temp[i];

		k=1;

		for (j=0;j<key;j++) {

			k=k*ct;

			k=k%n;

		}

		pt=k+96;

		m[i]=pt;

		i++;

	}

	m[i]=-1;

	printf("\nTHE DECRYPTED MESSAGE IS\n");

	for (i=0;m[i]!=-1;i++)

	printf("%c",m[i]);

}