Mercurial > dropbear
view libtommath/bn_mp_prime_random_ex.c @ 616:ae1df0cc3f18
Define LTC_NO_FILE to avoid hmac_file() etc
author | Matt Johnston <matt@ucc.asn.au> |
---|---|
date | Thu, 07 Apr 2011 13:24:41 +0000 |
parents | 5ff8218bcee9 |
children | 60fc6476e044 |
line wrap: on
line source
#include <tommath.h> #ifdef BN_MP_PRIME_RANDOM_EX_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, [email protected], http://math.libtomcrypt.com */ /* makes a truly random prime of a given size (bits), * * Flags are as follows: * * LTM_PRIME_BBS - make prime congruent to 3 mod 4 * LTM_PRIME_SAFE - make sure (p-1)/2 is prime as well (implies LTM_PRIME_BBS) * LTM_PRIME_2MSB_OFF - make the 2nd highest bit zero * LTM_PRIME_2MSB_ON - make the 2nd highest bit one * * You have to supply a callback which fills in a buffer with random bytes. "dat" is a parameter you can * have passed to the callback (e.g. a state or something). This function doesn't use "dat" itself * so it can be NULL * */ /* This is possibly the mother of all prime generation functions, muahahahahaha! */ int mp_prime_random_ex(mp_int *a, int t, int size, int flags, ltm_prime_callback cb, void *dat) { unsigned char *tmp, maskAND, maskOR_msb, maskOR_lsb; int res, err, bsize, maskOR_msb_offset; /* sanity check the input */ if (size <= 1 || t <= 0) { return MP_VAL; } /* LTM_PRIME_SAFE implies LTM_PRIME_BBS */ if (flags & LTM_PRIME_SAFE) { flags |= LTM_PRIME_BBS; } /* calc the byte size */ bsize = (size>>3) + ((size&7)?1:0); /* we need a buffer of bsize bytes */ tmp = OPT_CAST(unsigned char) XMALLOC(bsize); if (tmp == NULL) { return MP_MEM; } /* calc the maskAND value for the MSbyte*/ maskAND = ((size&7) == 0) ? 0xFF : (0xFF >> (8 - (size & 7))); /* calc the maskOR_msb */ maskOR_msb = 0; maskOR_msb_offset = ((size & 7) == 1) ? 1 : 0; if (flags & LTM_PRIME_2MSB_ON) { maskOR_msb |= 0x80 >> ((9 - size) & 7); } /* get the maskOR_lsb */ maskOR_lsb = 1; if (flags & LTM_PRIME_BBS) { maskOR_lsb |= 3; } do { /* read the bytes */ if (cb(tmp, bsize, dat) != bsize) { err = MP_VAL; goto error; } /* work over the MSbyte */ tmp[0] &= maskAND; tmp[0] |= 1 << ((size - 1) & 7); /* mix in the maskORs */ tmp[maskOR_msb_offset] |= maskOR_msb; tmp[bsize-1] |= maskOR_lsb; /* read it in */ if ((err = mp_read_unsigned_bin(a, tmp, bsize)) != MP_OKAY) { goto error; } /* is it prime? */ if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) { goto error; } if (res == MP_NO) { continue; } if (flags & LTM_PRIME_SAFE) { /* see if (a-1)/2 is prime */ if ((err = mp_sub_d(a, 1, a)) != MP_OKAY) { goto error; } if ((err = mp_div_2(a, a)) != MP_OKAY) { goto error; } /* is it prime? */ if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) { goto error; } } } while (res == MP_NO); if (flags & LTM_PRIME_SAFE) { /* restore a to the original value */ if ((err = mp_mul_2(a, a)) != MP_OKAY) { goto error; } if ((err = mp_add_d(a, 1, a)) != MP_OKAY) { goto error; } } err = MP_OKAY; error: XFREE(tmp); return err; } #endif /* $Source: /cvs/libtom/libtommath/bn_mp_prime_random_ex.c,v $ */ /* $Revision: 1.4 $ */ /* $Date: 2006/03/31 14:18:44 $ */