Mercurial > dropbear
view libtomcrypt/src/misc/mem_neq.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 | 6dba84798cd5 |
children |
line wrap: on
line source
/* LibTomCrypt, modular cryptographic library -- Tom St Denis * * LibTomCrypt is a library that provides various cryptographic * algorithms in a highly modular and flexible manner. * * The library is free for all purposes without any express * guarantee it works. */ #include "tomcrypt.h" /** @file mem_neq.c Compare two blocks of memory for inequality in constant time. Steffen Jaeckel */ /** Compare two blocks of memory for inequality in constant time. The usage is similar to that of standard memcmp, but you can only test if the memory is equal or not - you can not determine by how much the first different byte differs. This function shall be used to compare results of cryptographic operations where inequality means most likely usage of a wrong key. The execution time has therefore to be constant as otherwise timing attacks could be possible. @param a The first memory region @param b The second memory region @param len The length of the area to compare (octets) @return 0 when a and b are equal for len bytes, 1 they are not equal. */ int mem_neq(const void *a, const void *b, size_t len) { unsigned char ret = 0; const unsigned char* pa; const unsigned char* pb; LTC_ARGCHK(a != NULL); LTC_ARGCHK(b != NULL); pa = a; pb = b; while (len-- > 0) { ret |= *pa ^ *pb; ++pa; ++pb; } ret |= ret >> 4; ret |= ret >> 2; ret |= ret >> 1; ret &= 1; return ret; } /* ref: $Format:%D$ */ /* git commit: $Format:%H$ */ /* commit time: $Format:%ai$ */