Mercurial > dropbear
view libtommath/bn_s_mp_mul_digs_fast.c @ 1861:2b3a8026a6ce
Add re-exec for server
This allows ASLR to re-randomize the address
space for every connection, preventing some
vulnerabilities from being exploitable by
repeated probing.
Overhead (memory and time) is yet to be confirmed.
At present this is only enabled on Linux. Other BSD platforms
with fexecve() would probably also work though have not been tested.
author | Matt Johnston <matt@ucc.asn.au> |
---|---|
date | Sun, 30 Jan 2022 10:14:56 +0800 |
parents | 1051e4eea25a |
children |
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#include "tommath_private.h" #ifdef BN_S_MP_MUL_DIGS_FAST_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ /* Fast (comba) multiplier * * This is the fast column-array [comba] multiplier. It is * designed to compute the columns of the product first * then handle the carries afterwards. This has the effect * of making the nested loops that compute the columns very * simple and schedulable on super-scalar processors. * * This has been modified to produce a variable number of * digits of output so if say only a half-product is required * you don't have to compute the upper half (a feature * required for fast Barrett reduction). * * Based on Algorithm 14.12 on pp.595 of HAC. * */ mp_err s_mp_mul_digs_fast(const mp_int *a, const mp_int *b, mp_int *c, int digs) { int olduse, pa, ix, iz; mp_err err; mp_digit W[MP_WARRAY]; mp_word _W; /* grow the destination as required */ if (c->alloc < digs) { if ((err = mp_grow(c, digs)) != MP_OKAY) { return err; } } /* number of output digits to produce */ pa = MP_MIN(digs, a->used + b->used); /* clear the carry */ _W = 0; for (ix = 0; ix < pa; ix++) { int tx, ty; int iy; mp_digit *tmpx, *tmpy; /* get offsets into the two bignums */ ty = MP_MIN(b->used-1, ix); tx = ix - ty; /* setup temp aliases */ tmpx = a->dp + tx; tmpy = b->dp + ty; /* this is the number of times the loop will iterrate, essentially while (tx++ < a->used && ty-- >= 0) { ... } */ iy = MP_MIN(a->used-tx, ty+1); /* execute loop */ for (iz = 0; iz < iy; ++iz) { _W += (mp_word)*tmpx++ * (mp_word)*tmpy--; } /* store term */ W[ix] = (mp_digit)_W & MP_MASK; /* make next carry */ _W = _W >> (mp_word)MP_DIGIT_BIT; } /* setup dest */ olduse = c->used; c->used = pa; { mp_digit *tmpc; tmpc = c->dp; for (ix = 0; ix < pa; ix++) { /* now extract the previous digit [below the carry] */ *tmpc++ = W[ix]; } /* clear unused digits [that existed in the old copy of c] */ MP_ZERO_DIGITS(tmpc, olduse - ix); } mp_clamp(c); return MP_OKAY; } #endif