view libtomcrypt/src/encauth/ocb3/ocb3_int_xor_blocks.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
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/* 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.
 */

/**
   @file ocb3_int_xor_blocks.c
   OCB implementation, INTERNAL ONLY helper, by Karel Miko
*/
#include "tomcrypt.h"

#ifdef LTC_OCB3_MODE

/**
   Compute xor for two blocks of bytes 'out = block_a XOR block_b' (internal function)
   @param out        The block of bytes (output)
   @param block_a    The block of bytes (input)
   @param block_b    The block of bytes (input)
   @param block_len  The size of block_a, block_b, out
*/
void ocb3_int_xor_blocks(unsigned char *out, const unsigned char *block_a, const unsigned char *block_b, unsigned long block_len)
{
   int x;
   if (out == block_a) {
     for (x = 0; x < (int)block_len; x++) out[x] ^= block_b[x];
   }
   else {
     for (x = 0; x < (int)block_len; x++) out[x] = block_a[x] ^ block_b[x];
   }
}

#endif

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