annotate libtommath/bn_mp_add.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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1 #include "tommath_private.h"
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2 #ifdef BN_MP_ADD_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
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4 /* SPDX-License-Identifier: Unlicense */
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6 /* high level addition (handles signs) */
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7 mp_err mp_add(const mp_int *a, const mp_int *b, mp_int *c)
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8 {
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9 mp_sign sa, sb;
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10 mp_err err;
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11
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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12 /* get sign of both inputs */
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parents: 1470
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13 sa = a->sign;
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14 sb = b->sign;
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15
1655
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16 /* handle two cases, not four */
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17 if (sa == sb) {
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18 /* both positive or both negative */
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19 /* add their magnitudes, copy the sign */
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20 c->sign = sa;
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21 err = s_mp_add(a, b, c);
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22 } else {
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23 /* one positive, the other negative */
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24 /* subtract the one with the greater magnitude from */
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25 /* the one of the lesser magnitude. The result gets */
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26 /* the sign of the one with the greater magnitude. */
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27 if (mp_cmp_mag(a, b) == MP_LT) {
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28 c->sign = sb;
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29 err = s_mp_sub(b, a, c);
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30 } else {
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31 c->sign = sa;
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32 err = s_mp_sub(a, b, c);
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33 }
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34 }
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35 return err;
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36 }
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38 #endif