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view libtommath/bn_mp_to_ubin.c @ 1790:42745af83b7d

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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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#include "tommath_private.h"
#ifdef BN_MP_TO_UBIN_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

/* store in unsigned [big endian] format */
mp_err mp_to_ubin(const mp_int *a, unsigned char *buf, size_t maxlen, size_t *written)
{
   size_t  x, count;
   mp_err  err;
   mp_int  t;

   count = mp_ubin_size(a);
   if (count > maxlen) {
      return MP_BUF;
   }

   if ((err = mp_init_copy(&t, a)) != MP_OKAY) {
      return err;
   }

   for (x = count; x --> 0u;) {
#ifndef MP_8BIT
      buf[x] = (unsigned char)(t.dp[0] & 255u);
#else
      buf[x] = (unsigned char)(t.dp[0] | ((t.dp[1] & 1u) << 7));
#endif
      if ((err = mp_div_2d(&t, 8, &t, NULL)) != MP_OKAY) {
         goto LBL_ERR;
      }
   }

   if (written != NULL) {
      *written = count;
   }

LBL_ERR:
   mp_clear(&t);
   return err;
}
#endif