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Diffstat (limited to 'libtommath/bn_mp_prime_rand.c')
| -rw-r--r-- | libtommath/bn_mp_prime_rand.c | 141 |
1 files changed, 141 insertions, 0 deletions
diff --git a/libtommath/bn_mp_prime_rand.c b/libtommath/bn_mp_prime_rand.c new file mode 100644 index 0000000..4530e9a --- /dev/null +++ b/libtommath/bn_mp_prime_rand.c @@ -0,0 +1,141 @@ +#include "tommath_private.h" +#ifdef BN_MP_PRIME_RAND_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: + * + * MP_PRIME_BBS - make prime congruent to 3 mod 4 + * MP_PRIME_SAFE - make sure (p-1)/2 is prime as well (implies MP_PRIME_BBS) + * MP_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! */ +mp_err s_mp_prime_random_ex(mp_int *a, int t, int size, int flags, private_mp_prime_callback cb, void *dat) +{ + unsigned char *tmp, maskAND, maskOR_msb, maskOR_lsb; + int bsize, maskOR_msb_offset; + mp_bool res; + mp_err err; + + /* sanity check the input */ + if ((size <= 1) || (t <= 0)) { + return MP_VAL; + } + + /* MP_PRIME_SAFE implies MP_PRIME_BBS */ + if ((flags & MP_PRIME_SAFE) != 0) { + flags |= MP_PRIME_BBS; + } + + /* calc the byte size */ + bsize = (size>>3) + ((size&7)?1:0); + + /* we need a buffer of bsize bytes */ + tmp = (unsigned char *) MP_MALLOC((size_t)bsize); + if (tmp == NULL) { + return MP_MEM; + } + + /* calc the maskAND value for the MSbyte*/ + maskAND = ((size&7) == 0) ? 0xFFu : (unsigned char)(0xFFu >> (8 - (size & 7))); + + /* calc the maskOR_msb */ + maskOR_msb = 0; + maskOR_msb_offset = ((size & 7) == 1) ? 1 : 0; + if ((flags & MP_PRIME_2MSB_ON) != 0) { + maskOR_msb |= (unsigned char)(0x80 >> ((9 - size) & 7)); + } + + /* get the maskOR_lsb */ + maskOR_lsb = 1u; + if ((flags & MP_PRIME_BBS) != 0) { + maskOR_lsb |= 3u; + } + + 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 */ + /* TODO: casting only for now until all lengths have been changed to the type "size_t"*/ + if ((err = mp_from_ubin(a, tmp, (size_t)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 & MP_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 & MP_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: + MP_FREE_BUFFER(tmp, (size_t)bsize); + return err; +} + +static int s_mp_rand_cb(unsigned char *dst, int len, void *dat) +{ + (void)dat; + if (len <= 0) { + return len; + } + if (s_mp_rand_source(dst, (size_t)len) != MP_OKAY) { + return 0; + } + return len; +} + +mp_err mp_prime_rand(mp_int *a, int t, int size, int flags) +{ + return s_mp_prime_random_ex(a, t, size, flags, s_mp_rand_cb, NULL); +} + +#endif |