#include "tommath_private.h" #ifdef BN_MP_PRIME_RANDOM_EX_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ /* 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_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) != 0) { flags |= LTM_PRIME_BBS; } /* calc the byte size */ bsize = (size>>3) + ((size&7)?1:0); /* we need a buffer of bsize bytes */ tmp = (unsigned char *) XMALLOC((size_t)bsize); if (tmp == NULL) { return MP_MEM; } /* calc the maskAND value for the MSbyte*/ maskAND = ((size&7) == 0) ? 0xFF : (unsigned char)(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) != 0) { maskOR_msb |= (unsigned char)(0x80 >> ((9 - size) & 7)); } /* get the maskOR_lsb */ maskOR_lsb = 1; if ((flags & LTM_PRIME_BBS) != 0) { 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] |= (unsigned char)(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) != 0) { /* see if (a-1)/2 is prime */ if ((err = mp_sub_d(a, 1uL, 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) != 0) { /* restore a to the original value */ if ((err = mp_mul_2(a, a)) != MP_OKAY) { goto error; } if ((err = mp_add_d(a, 1uL, a)) != MP_OKAY) { goto error; } } err = MP_OKAY; error: XFREE(tmp, bsize); return err; } #endif