Mercurial > dropbear
view libtommath/bn_mp_gcd.c @ 1715:3974f087d9c0
Disallow leading lines before the ident for server (#102)
Per RFC4253 4.2 clients must be able to process other lines of data
before the version string, server behavior is not defined neither
with MUST/SHOULD nor with MAY.
If server process up to 50 lines too - it may cause too long hanging
session with invalid/evil client that consume host resources and
potentially may lead to DDoS on poor embedded boxes.
Let's require first line from client to be version string and fail
early if it's not - matches both RFC and real OpenSSH behavior.
author | Vladislav Grishenko <themiron@users.noreply.github.com> |
---|---|
date | Mon, 15 Jun 2020 18:22:18 +0500 |
parents | 1051e4eea25a |
children |
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line source
#include "tommath_private.h" #ifdef BN_MP_GCD_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ /* Greatest Common Divisor using the binary method */ mp_err mp_gcd(const mp_int *a, const mp_int *b, mp_int *c) { mp_int u, v; int k, u_lsb, v_lsb; mp_err err; /* either zero than gcd is the largest */ if (MP_IS_ZERO(a)) { return mp_abs(b, c); } if (MP_IS_ZERO(b)) { return mp_abs(a, c); } /* get copies of a and b we can modify */ if ((err = mp_init_copy(&u, a)) != MP_OKAY) { return err; } if ((err = mp_init_copy(&v, b)) != MP_OKAY) { goto LBL_U; } /* must be positive for the remainder of the algorithm */ u.sign = v.sign = MP_ZPOS; /* B1. Find the common power of two for u and v */ u_lsb = mp_cnt_lsb(&u); v_lsb = mp_cnt_lsb(&v); k = MP_MIN(u_lsb, v_lsb); if (k > 0) { /* divide the power of two out */ if ((err = mp_div_2d(&u, k, &u, NULL)) != MP_OKAY) { goto LBL_V; } if ((err = mp_div_2d(&v, k, &v, NULL)) != MP_OKAY) { goto LBL_V; } } /* divide any remaining factors of two out */ if (u_lsb != k) { if ((err = mp_div_2d(&u, u_lsb - k, &u, NULL)) != MP_OKAY) { goto LBL_V; } } if (v_lsb != k) { if ((err = mp_div_2d(&v, v_lsb - k, &v, NULL)) != MP_OKAY) { goto LBL_V; } } while (!MP_IS_ZERO(&v)) { /* make sure v is the largest */ if (mp_cmp_mag(&u, &v) == MP_GT) { /* swap u and v to make sure v is >= u */ mp_exch(&u, &v); } /* subtract smallest from largest */ if ((err = s_mp_sub(&v, &u, &v)) != MP_OKAY) { goto LBL_V; } /* Divide out all factors of two */ if ((err = mp_div_2d(&v, mp_cnt_lsb(&v), &v, NULL)) != MP_OKAY) { goto LBL_V; } } /* multiply by 2**k which we divided out at the beginning */ if ((err = mp_mul_2d(&u, k, c)) != MP_OKAY) { goto LBL_V; } c->sign = MP_ZPOS; err = MP_OKAY; LBL_V: mp_clear(&u); LBL_U: mp_clear(&v); return err; } #endif