Mercurial > dropbear
view libtommath/bn_mp_mul_2d.c @ 1790:42745af83b7d
Introduce extra delay before closing unauthenticated sessions
To make it harder for attackers, introduce a delay to keep an
unauthenticated session open a bit longer, thus blocking a connection
slot until after the delay.
Without this, while there is a limit on the amount of attempts an attacker
can make at the same time (MAX_UNAUTH_PER_IP), the time taken by dropbear to
handle one attempt is still short and thus for each of the allowed parallel
attempts many attempts can be chained one after the other. The attempt rate
is then:
"MAX_UNAUTH_PER_IP / <process time of one attempt>".
With the delay, this rate becomes:
"MAX_UNAUTH_PER_IP / UNAUTH_CLOSE_DELAY".
author | Thomas De Schampheleire <thomas.de_schampheleire@nokia.com> |
---|---|
date | Wed, 15 Feb 2017 13:53:04 +0100 |
parents | 1051e4eea25a |
children |
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line source
#include "tommath_private.h" #ifdef BN_MP_MUL_2D_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ /* shift left by a certain bit count */ mp_err mp_mul_2d(const mp_int *a, int b, mp_int *c) { mp_digit d; mp_err err; /* copy */ if (a != c) { if ((err = mp_copy(a, c)) != MP_OKAY) { return err; } } if (c->alloc < (c->used + (b / MP_DIGIT_BIT) + 1)) { if ((err = mp_grow(c, c->used + (b / MP_DIGIT_BIT) + 1)) != MP_OKAY) { return err; } } /* shift by as many digits in the bit count */ if (b >= MP_DIGIT_BIT) { if ((err = mp_lshd(c, b / MP_DIGIT_BIT)) != MP_OKAY) { return err; } } /* shift any bit count < MP_DIGIT_BIT */ d = (mp_digit)(b % MP_DIGIT_BIT); if (d != 0u) { mp_digit *tmpc, shift, mask, r, rr; int x; /* bitmask for carries */ mask = ((mp_digit)1 << d) - (mp_digit)1; /* shift for msbs */ shift = (mp_digit)MP_DIGIT_BIT - d; /* alias */ tmpc = c->dp; /* carry */ r = 0; for (x = 0; x < c->used; x++) { /* get the higher bits of the current word */ rr = (*tmpc >> shift) & mask; /* shift the current word and OR in the carry */ *tmpc = ((*tmpc << d) | r) & MP_MASK; ++tmpc; /* set the carry to the carry bits of the current word */ r = rr; } /* set final carry */ if (r != 0u) { c->dp[(c->used)++] = r; } } mp_clamp(c); return MP_OKAY; } #endif