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Diffstat (limited to 'libtommath/bn_mp_prime_random_ex.c')
| -rw-r--r-- | libtommath/bn_mp_prime_random_ex.c | 123 |
1 files changed, 123 insertions, 0 deletions
diff --git a/libtommath/bn_mp_prime_random_ex.c b/libtommath/bn_mp_prime_random_ex.c new file mode 100644 index 0000000..2010ebe --- /dev/null +++ b/libtommath/bn_mp_prime_random_ex.c @@ -0,0 +1,123 @@ +#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, tomstdenis@iahu.ca, http://math.libtomcrypt.org + */ + +/* 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 - 2) >> 3; + if (flags & LTM_PRIME_2MSB_ON) { + maskOR_msb |= 1 << ((size - 2) & 7); + } else if (flags & LTM_PRIME_2MSB_OFF) { + maskAND &= ~(1 << ((size - 2) & 7)); + } + + /* get the maskOR_lsb */ + maskOR_lsb = 0; + 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 |