/* Generates provable primes
*
* See http://gmail.com:8080/papers/pp.pdf for more info.
*
* Tom St Denis, tomstdenis@gmail.com, http://tom.gmail.com
*/
#include <time.h>
#include "tommath.h"
int n_prime;
FILE *primes;
/* fast square root */
static mp_digit
i_sqrt (mp_word x)
{
mp_word x1, x2;
x2 = x;
do {
x1 = x2;
x2 = x1 - ((x1 * x1) - x) / (2 * x1);
} while (x1 != x2);
if (x1 * x1 > x) {
--x1;
}
return x1;
}
/* generates a prime digit */
static void gen_prime (void)
{
mp_digit r, x, y, next;
FILE *out;
out = fopen("pprime.dat", "wb");
/* write first set of primes */
r = 3; fwrite(&r, 1, sizeof(mp_digit), out);
r = 5; fwrite(&r, 1, sizeof(mp_digit), out);
r = 7; fwrite(&r, 1, sizeof(mp_digit), out);
r = 11; fwrite(&r, 1, sizeof(mp_digit), out);
r = 13; fwrite(&r, 1, sizeof(mp_digit), out);
r = 17; fwrite(&r, 1, sizeof(mp_digit), out);
r = 19; fwrite(&r, 1, sizeof(mp_digit), out);
r = 23; fwrite(&r, 1, sizeof(mp_digit), out);
r = 29; fwrite(&r, 1, sizeof(mp_digit), out);
r = 31; fwrite(&r, 1, sizeof(mp_digit), out);
/* get square root, since if 'r' is composite its factors must be < than this */
y = i_sqrt (r);
next = (y + 1) * (y + 1);
for (;;) {
do {
r += 2; /* next candidate */
r &= MP_MASK;
if (r < 31) break;
/* update sqrt ? */
if (next <= r) {
++y;
next = (y + 1) * (y + 1);
}
/* loop if divisible by 3,5,7,11,13,17,19,23,29 */
if ((r % 3) == 0) {
x = 0;
continue;
}
if ((r % 5) == 0) {
x = 0;
continue;
}
if ((r % 7) == 0) {
x = 0;
continue;
}
if ((r % 11) == 0) {
x = 0;
continue;
}
if ((r % 13) == 0) {
x = 0;
continue;
}
if ((r % 17) == 0) {
x = 0;
continue;
}
if ((r % 19) == 0) {
x = 0;
continue;
}
if ((r % 23) == 0) {
x = 0;
continue;
}
if ((r % 29) == 0) {
x = 0;
continue;
}
/* now check if r is divisible by x + k={1,7,11,13,17,19,23,29} */
for (x = 30; x <= y; x += 30) {
if ((r % (x + 1)) == 0) {
x = 0;
break;
}
if ((r % (x + 7)) == 0) {
x = 0;
break;
}
if ((r % (x + 11)) == 0) {
x = 0;
break;
}
if ((r % (x + 13)) == 0) {
x = 0;
break;
}
if ((r % (x + 17)) == 0) {
x = 0;
break;
}
if ((r % (x + 19)) == 0) {
x = 0;
break;
}
if ((r % (x + 23)) == 0) {
x = 0;
break;
}
if ((r % (x + 29)) == 0) {
x = 0;
break;
}
}
} while (x == 0);
if (r > 31) { fwrite(&r, 1, sizeof(mp_digit), out); printf("%9d\r", r); fflush(stdout); }
if (r < 31) break;
}
fclose(out);
}
void load_tab(void)
{
primes = fopen("pprime.dat", "rb");
if (primes == NULL) {
gen_prime();
primes = fopen("pprime.dat", "rb");
}
fseek(primes, 0, SEEK_END);
n_prime = ftell(primes) / sizeof(mp_digit);
}
mp_digit prime_digit(void)
{
int n;
mp_digit d;
n = abs(rand()) % n_prime;
fseek(primes, n * sizeof(mp_digit), SEEK_SET);
fread(&d, 1, sizeof(mp_digit), primes);
return d;
}
/* makes a prime of at least k bits */
int
pprime (int k, int li, mp_int * p, mp_int * q)
{
mp_int a, b, c, n, x, y, z, v;
int res, ii;
static const mp_digit bases[] = { 2, 3, 5, 7, 11, 13, 17, 19 };
/* single digit ? */
if (k <= (int) DIGIT_BIT) {
mp_set (p, prime_digit ());
return MP_OKAY;
}
if ((res = mp_init (&c)) != MP_OKAY) {
return res;
}
if ((res = mp_init (&v)) != MP_OKAY) {
goto LBL_C;
}
/* product of first 50 primes */
if ((res =
mp_read_radix (&v,
"19078266889580195013601891820992757757219839668357012055907516904309700014933909014729740190",
10)) != MP_OKAY) {
goto LBL_V;
}
if ((res = mp_init (&a)) != MP_OKAY) {
goto LBL_V;
}
/* set the prime */
mp_set (&a, prime_digit ());
if ((res = mp_init (&b)) != MP_OKAY) {
goto LBL_A;
}
if ((res = mp_init (&n)) != MP_OKAY) {
goto LBL_B;
}
if ((res = mp_init (&x)) != MP_OKAY) {
goto LBL_N;
}
if ((res = mp_init (&y)) != MP_OKAY) {
goto LBL_X;
}
if ((res = mp_init (&z)) != MP_OKAY) {
goto LBL_Y;
}
/* now loop making the single digit */
while (mp_count_bits (&a) < k) {
fprintf (stderr, "prime has %4d bits left\r", k - mp_count_bits (&a));
fflush (stderr);
top:
mp_set (&b, prime_digit ());
/* now compute z = a * b * 2 */
if ((res = mp_mul (&a, &b, &z)) != MP_OKAY) { /* z = a * b */
goto LBL_Z;
}
if ((res = mp_copy (&z, &c)) != MP_OKAY) { /* c = a * b */
goto LBL_Z;
}
if ((res = mp_mul_2 (&z, &z)) != MP_OKAY) { /* z = 2 * a * b */
goto LBL_Z;
}
/* n = z + 1 */
if ((res = mp_add_d (&z, 1, &n)) != MP_OKAY) { /* n = z + 1 */
goto LBL_Z;
}
/* check (n, v) == 1 */
if ((res = mp_gcd (&n, &v, &y)) != MP_OKAY) { /* y = (n, v) */
goto LBL_Z;
}
if (mp_cmp_d (&y, 1) != MP_EQ)
goto top;
/* now try base x=bases[ii] */
for (ii = 0; ii < li; ii++) {
mp_set (&x, bases[ii]);
/* compute x^a mod n */
if ((res = mp_exptmod (&x, &a, &n, &y)) != MP_OKAY) { /* y = x^a mod n */
goto LBL_Z;
}
/* if y == 1 loop */
if (mp_cmp_d (&y, 1) == MP_EQ)
continue;
/* now x^2a mod n */
if ((res = mp_sqrmod (&y, &n, &y)) != MP_OKAY) { /* y = x^2a mod n */
goto LBL_Z;
}
if (mp_cmp_d (&y, 1) == MP_EQ)
continue;
/* compute x^b mod n */
if ((res = mp_exptmod (&x, &b, &n, &y)) != MP_OKAY) { /* y = x^b mod n */
goto LBL_Z;
}
/* if y == 1 loop */
if (mp_cmp_d (&y, 1) == MP_EQ)
continue;
/* now x^2b mod n */
if ((res = mp_sqrmod (&y, &n, &y)) != MP_OKAY) { /* y = x^2b mod n */
goto LBL_Z;
}
if (mp_cmp_d (&y, 1) == MP_EQ)
continue;
/* compute x^c mod n == x^ab mod n */
if ((res = mp_exptmod (&x, &c, &n, &y)) != MP_OKAY) { /* y = x^ab mod n */
goto LBL_Z;
}
/* if y == 1 loop */
if (mp_cmp_d (&y, 1) == MP_EQ)
continue;
/* now compute (x^c mod n)^2 */
if ((res = mp_sqrmod (&y, &n, &y)) != MP_OKAY) { /* y = x^2ab mod n */
goto LBL_Z;
}
/* y should be 1 */
if (mp_cmp_d (&y, 1) != MP_EQ)
continue;
break;
}
/* no bases worked? */
if (ii == li)
goto top;
{
char buf[4096];
mp_toradix(&n, buf, 10);
printf("Certificate of primality for:\n%s\n\n", buf);
mp_toradix(&a, buf, 10);
printf("A == \n%s\n\n", buf);
mp_toradix(&b, buf, 10);
printf("B == \n%s\n\nG == %d\n", buf, bases[ii]);
printf("----------------------------------------------------------------\n");
}
/* a = n */
mp_copy (&n, &a);
}
/* get q to be the order of the large prime subgroup */
mp_sub_d (&n, 1, q);
mp_div_2 (q, q);
mp_div (q, &b, q, NULL);
mp_exch (&n, p);
res = MP_OKAY;
LBL_Z:mp_clear (&z);
LBL_Y:mp_clear (&y);
LBL_X:mp_clear (&x);
LBL_N:mp_clear (&n);
LBL_B:mp_clear (&b);
LBL_A:mp_clear (&a);
LBL_V:mp_clear (&v);
LBL_C:mp_clear (&c);
return res;
}
int
main (void)
{
mp_int p, q;
char buf[4096];
int k, li;
clock_t t1;
srand (time (NULL));
load_tab();
printf ("Enter # of bits: \n");
fgets (buf, sizeof (buf), stdin);
sscanf (buf, "%d", &k);
printf ("Enter number of bases to try (1 to 8):\n");
fgets (buf, sizeof (buf), stdin);
sscanf (buf, "%d", &li);
mp_init (&p);
mp_init (&q);
t1 = clock ();
pprime (k, li, &p, &q);
t1 = clock () - t1;
printf ("\n\nTook %ld ticks, %d bits\n", t1, mp_count_bits (&p));
mp_toradix (&p, buf, 10);
printf ("P == %s\n", buf);
mp_toradix (&q, buf, 10);
printf ("Q == %s\n", buf);
return 0;
}
/* $Source$ */
/* $Revision$ */
/* $Date$ */
