Mercurial > dropbear
view libtommath/bn_mp_lcm.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_LCM_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ /* computes least common multiple as |a*b|/(a, b) */ mp_err mp_lcm(const mp_int *a, const mp_int *b, mp_int *c) { mp_err err; mp_int t1, t2; if ((err = mp_init_multi(&t1, &t2, NULL)) != MP_OKAY) { return err; } /* t1 = get the GCD of the two inputs */ if ((err = mp_gcd(a, b, &t1)) != MP_OKAY) { goto LBL_T; } /* divide the smallest by the GCD */ if (mp_cmp_mag(a, b) == MP_LT) { /* store quotient in t2 such that t2 * b is the LCM */ if ((err = mp_div(a, &t1, &t2, NULL)) != MP_OKAY) { goto LBL_T; } err = mp_mul(b, &t2, c); } else { /* store quotient in t2 such that t2 * a is the LCM */ if ((err = mp_div(b, &t1, &t2, NULL)) != MP_OKAY) { goto LBL_T; } err = mp_mul(a, &t2, c); } /* fix the sign to positive */ c->sign = MP_ZPOS; LBL_T: mp_clear_multi(&t1, &t2, NULL); return err; } #endif