/*
 * keygen.cpp
 *
 *
 */

#include "keygen.h"
#include "miller_rabin.h"

#ifndef DEBUG
#define DEBUG
#endif

/* forward declaration of variables from keygen_args.h */
extern char *pubkey;
extern char *prikey;
extern long prime_p;
extern long prime_q;
extern int random_f;

unsigned long gcd(unsigned long x, unsigned long y)
{
    while (x != y)
    {
        if (x > y)
            x -= y;
        else
            y -= x;
    }

    return x;
}

unsigned short gen_prime(void)
{
    unsigned short prime_gen = rand();

    /* tips from http://www.di-mgt.com.au/rsa_alg.html */
    prime_gen |= LOW_BIT_ON;
    prime_gen |= FIRST_TWO_BITS_ON;

    while (!miller_rabin_16(prime_gen))
        prime_gen += 2;

    return prime_gen;
}

int main(int argc, char **argv)
{
    /* seed rand() */
    srand((unsigned int ) time(NULL));

    if (keygen_args(argc, argv) == 0)
        cout << "read arguments successfully" << endl;

    if (random_f)
    {
        printf("generating random primes...\n");
        prime_p = gen_prime();
        printf("generated p: %hu\n", (unsigned short) prime_p);

        prime_q = gen_prime();
        printf("generated q: %hu\n", (unsigned short) prime_q);
    }

    /* n = p * q */
    unsigned long n = prime_p * prime_q;
    if (n <= 127)
    {
        fprintf(stderr, "p * q needs to be bigger than 127\n");
        exit(EXIT_FAILURE);
    }

    /* phi = (p-1)(q-1) */
    unsigned long phi = (prime_p-1) * (prime_q-1);

    unsigned long fermat_primes[4] = { 3l, 17l, 19l, 31l };
    unsigned long e;
    /* find e, 1 < e < phi, such that gcd(e, phi) = 1 */
    int i;
    printf("computing e... ");
    for (i = 0; i < 4; i++)
    {
        e = fermat_primes[i];
        if (gcd(e, phi) == 1)
            break;
    }
    if (i == 4)
    {
        fprintf(stderr, "error, could not find e\n");
        exit(EXIT_FAILURE);
    }
    printf("done\n");

    /* find d */
    printf("computing d... (might take a while) ");
    fflush(stdout);
    unsigned long d = 1;
    while (1)
    {
        if ( ((e*d) % phi) == 1 )
            break;

        d++;
    }
    printf("done\n");

#ifdef DEBUG
    printf("debug: pubkey = \"%s\"\n"
           "       prikey = \"%s\"\n"
           "       p      = \"%ld\"\n"
           "       q      = \"%ld\"\n"
           "       n      = \"%lu\"\n"
           "       phi    = \"%lu\"\n"
           "       e      = \"%lu\"\n"
           "       d      = \"%lu\"\n",
           pubkey, prikey, prime_p, prime_q, n, phi, e, d);
#endif

    /* save to xml files */
    FILE *public_key =  fopen(pubkey, "w");
    FILE *private_key = fopen(prikey, "w");
    if (public_key == NULL || private_key == NULL)
    {
        perror("fopen");
        exit(EXIT_FAILURE);
    }

    fprintf(public_key, "<rsakey>\n");
    fprintf(public_key, "\t<evalue>%lu</evalue>\n", e);
    fprintf(public_key, "\t<nvalue>%lu</nvalue>\n", n);
    fprintf(public_key, "</rsakey>\n");
    printf("wrote \"%s\" file\n", pubkey);

    fprintf(private_key, "<rsakey>\n");
    fprintf(private_key, "\t<dvalue>%lu</dvalue>\n", d);
    fprintf(private_key, "\t<nvalue>%lu</nvalue>\n", n);
    fprintf(private_key, "</rsakey>\n");
    printf("wrote \"%s\" file\n", prikey);

    fclose(public_key);
    fclose(private_key);

    return 0;
}