1 0fc65b37 2004-03-21 devnull #include "os.h"
2 0fc65b37 2004-03-21 devnull #include <mp.h>
3 0fc65b37 2004-03-21 devnull #include <libsec.h>
5 cbeb0b26 2006-04-01 devnull /* Gordon's algorithm for generating a strong prime */
6 cbeb0b26 2006-04-01 devnull /* Menezes et al () Handbook, p.150 */
8 0fc65b37 2004-03-21 devnull genstrongprime(mpint *p, int n, int accuracy)
10 0fc65b37 2004-03-21 devnull mpint *s, *t, *r, *i;
12 0fc65b37 2004-03-21 devnull if(n < 64)
15 0fc65b37 2004-03-21 devnull s = mpnew(n/2);
16 0fc65b37 2004-03-21 devnull genprime(s, (n/2)-16, accuracy);
17 0fc65b37 2004-03-21 devnull t = mpnew(n/2);
18 0fc65b37 2004-03-21 devnull genprime(t, n-mpsignif(s)-32, accuracy);
20 cbeb0b26 2006-04-01 devnull /* first r = 2it + 1 that's prime */
21 0fc65b37 2004-03-21 devnull i = mpnew(16);
22 0fc65b37 2004-03-21 devnull r = mpnew(0);
23 0fc65b37 2004-03-21 devnull itomp(0x8000, i);
24 cbeb0b26 2006-04-01 devnull mpleft(t, 1, t); /* 2t */
25 cbeb0b26 2006-04-01 devnull mpmul(i, t, r); /* 2it */
26 cbeb0b26 2006-04-01 devnull mpadd(r, mpone, r); /* 2it + 1 */
28 0fc65b37 2004-03-21 devnull if(probably_prime(r, 18))
30 cbeb0b26 2006-04-01 devnull mpadd(r, t, r); /* r += 2t */
33 cbeb0b26 2006-04-01 devnull /* p0 = 2(s**(r-2) mod r)s - 1 */
34 0fc65b37 2004-03-21 devnull itomp(2, p);
35 0fc65b37 2004-03-21 devnull mpsub(r, p, p);
36 0fc65b37 2004-03-21 devnull mpexp(s, p, r, p);
37 0fc65b37 2004-03-21 devnull mpmul(s, p, p);
38 0fc65b37 2004-03-21 devnull mpleft(p, 1, p);
39 0fc65b37 2004-03-21 devnull mpsub(p, mpone, p);
41 cbeb0b26 2006-04-01 devnull /* first p = p0 + 2irs that's prime */
42 0fc65b37 2004-03-21 devnull itomp(0x8000, i);
43 cbeb0b26 2006-04-01 devnull mpleft(r, 1, r); /* 2r */
44 cbeb0b26 2006-04-01 devnull mpmul(r, s, r); /* 2rs */
45 cbeb0b26 2006-04-01 devnull mpmul(r, i, i); /* 2irs */
46 cbeb0b26 2006-04-01 devnull mpadd(p, i, p); /* p0 + 2irs */
48 0fc65b37 2004-03-21 devnull if(probably_prime(p, accuracy))
50 cbeb0b26 2006-04-01 devnull mpadd(p, r, p); /* p += 2rs */
53 0fc65b37 2004-03-21 devnull mpfree(i);
54 0fc65b37 2004-03-21 devnull mpfree(s);
55 0fc65b37 2004-03-21 devnull mpfree(r);
56 0fc65b37 2004-03-21 devnull mpfree(t);