Mercurial > dropbear

annotate libtommath/bn_s_mp_balance_mul.c @ 1788:1fc0012b9c38

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Fix handling of replies to global requests (#112) The current code assumes that all global requests want / need a reply. This isn't always true and the request itself indicates if it wants a reply or not. It causes a specific problem with [email protected] messages. These are sent by OpenSSH after authentication to inform the client of potential other host keys for the host. This can be used to add a new type of host key or to rotate host keys. The initial information message from the server is sent as a global request, but with want_reply set to false. This means that the server doesn't expect an answer to this message. Instead the client needs to send a prove request as a reply if it wants to receive proof of ownership for the host keys. The bug doesn't cause any current problems with due to how OpenSSH treats receiving the failure message. It instead treats it as a keepalive message and further ignores it. Arguably this is a protocol violation though of Dropbear and it is only accidental that it doesn't cause a problem with OpenSSH. The bug was found when adding host keys support to libssh, which is more strict protocol wise and treats the unexpected failure message an error, also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145 for more information. The fix here is to honor the want_reply flag in the global request and to only send a reply if the other side expects a reply.
author Dirkjan Bussink <d.bussink@gmail.com>
date Thu, 10 Dec 2020 16:13:13 +0100
parents 1051e4eea25a
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
1692
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
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1 #include "tommath_private.h"
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2 #ifdef BN_S_MP_BALANCE_MUL_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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5
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6 /* single-digit multiplication with the smaller number as the single-digit */
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7 mp_err s_mp_balance_mul(const mp_int *a, const mp_int *b, mp_int *c)
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8 {
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9 int count, len_a, len_b, nblocks, i, j, bsize;
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10 mp_int a0, tmp, A, B, r;
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11 mp_err err;
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12
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13 len_a = a->used;
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14 len_b = b->used;
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15
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16 nblocks = MP_MAX(a->used, b->used) / MP_MIN(a->used, b->used);
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17 bsize = MP_MIN(a->used, b->used) ;
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18
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19 if ((err = mp_init_size(&a0, bsize + 2)) != MP_OKAY) {
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20 return err;
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21 }
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22 if ((err = mp_init_multi(&tmp, &r, NULL)) != MP_OKAY) {
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23 mp_clear(&a0);
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24 return err;
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25 }
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26
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27 /* Make sure that A is the larger one*/
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28 if (len_a < len_b) {
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29 B = *a;
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30 A = *b;
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31 } else {
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32 A = *a;
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33 B = *b;
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34 }
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35
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36 for (i = 0, j=0; i < nblocks; i++) {
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37 /* Cut a slice off of a */
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38 a0.used = 0;
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39 for (count = 0; count < bsize; count++) {
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40 a0.dp[count] = A.dp[ j++ ];
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41 a0.used++;
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42 }
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43 mp_clamp(&a0);
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44 /* Multiply with b */
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45 if ((err = mp_mul(&a0, &B, &tmp)) != MP_OKAY) {
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46 goto LBL_ERR;
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47 }
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48 /* Shift tmp to the correct position */
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49 if ((err = mp_lshd(&tmp, bsize * i)) != MP_OKAY) {
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50 goto LBL_ERR;
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51 }
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52 /* Add to output. No carry needed */
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53 if ((err = mp_add(&r, &tmp, &r)) != MP_OKAY) {
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54 goto LBL_ERR;
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55 }
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56 }
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57 /* The left-overs; there are always left-overs */
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58 if (j < A.used) {
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59 a0.used = 0;
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60 for (count = 0; j < A.used; count++) {
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61 a0.dp[count] = A.dp[ j++ ];
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62 a0.used++;
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63 }
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64 mp_clamp(&a0);
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65 if ((err = mp_mul(&a0, &B, &tmp)) != MP_OKAY) {
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66 goto LBL_ERR;
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67 }
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68 if ((err = mp_lshd(&tmp, bsize * i)) != MP_OKAY) {
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69 goto LBL_ERR;
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70 }
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71 if ((err = mp_add(&r, &tmp, &r)) != MP_OKAY) {
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72 goto LBL_ERR;
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73 }
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74 }
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75
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76 mp_exch(&r,c);
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77 LBL_ERR:
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78 mp_clear_multi(&a0, &tmp, &r,NULL);
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79 return err;
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80 }
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81 #endif