/*********************************************************************
 *   pgp_calc.cc -- This calculates and displays all other PGP related
 *   exponents/numbers from only P, Q, (the two factors of N), and E, the
 *   public exponent.  E is normaly publicly available, and P and Q must
 *   be found from N.
 *
 *   Requires a large integer library (such as GMP) and a class named
 *   "Integer" that supports it (+, -, *, etc.) in the <Integer.h> file. 
 *
 * Compile:
 *    g++ -o pgp_calc pgp_calc.cc libgmp.a
 * Invoke:
 *    ./pgp_calc [P] [Q] [E]
 * Changelog:
 *   971024: Created - Paul Herman <a540pau@pslc.ucla.edu>
 ******************************************************************/

#include <Integer.h>

int main(int argc, char **argv) {
	Integer p, q, n, jn, d, e, u;
	int count, arg;

	count = argc - 1;	// # of ints given
	p=0; q=0; e=0;
	if (count > 0 && argv[1][0] == '-') {
		cerr << "Usage: " << argv[0] << " [P] [Q] [E]" << endl;
		cerr << "   P, Q -- factors of public modulus, N" << endl;
		cerr << "   E    -- public exponent" << endl;
		return -1;
		}
	if (count > 0) p = argv[1];
	else {cout << "Enter the first factor of N (P):"; cin >> p;}
	if (count > 1) q = argv[2];
	else {cout << "Enter the second factor of N (Q):"; cin >> q;}
	if (count > 2) e = argv[3];
	else {cout << "Enter the public exponent (E):"; cin >> e;}

	n = p*q;			// N = P*Q
	jn = (p-1) * (q-1);		// J(N) = Euler Totient function
	d = InvModN(e, jn);		// E*D = 1 (mod J(N))
	if (p<q) u = InvModN(p, q);	// P*U = 1 (mod Q)   if P<Q
	else u = InvModN(q, p);

	cout << "Pub Modulus  (N): " << n << endl;
	cout << "Euler Tot.  J(N): " << jn << endl;
	cout << "Pub Exponent (E): " << e << endl;
	cout << "Sec Exponent (D): " << d << endl;
	cout << "Mul Inverse  (U): " << u << endl;

}