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annotate libtommath/bn_mp_to_radix.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_MP_TO_RADIX_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 /* stores a bignum as a ASCII string in a given radix (2..64)
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7 *
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8 * Stores upto "size - 1" chars and always a NULL byte, puts the number of characters
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9 * written, including the '\0', in "written".
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10 */
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11 mp_err mp_to_radix(const mp_int *a, char *str, size_t maxlen, size_t *written, int radix)
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12 {
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13 size_t digs;
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14 mp_err err;
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15 mp_int t;
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16 mp_digit d;
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17 char *_s = str;
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18
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19 /* check range of radix and size*/
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20 if (maxlen < 2u) {
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21 return MP_BUF;
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22 }
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23 if ((radix < 2) || (radix > 64)) {
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24 return MP_VAL;
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25 }
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26
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27 /* quick out if its zero */
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28 if (MP_IS_ZERO(a)) {
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29 *str++ = '0';
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30 *str = '\0';
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31 if (written != NULL) {
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32 *written = 2u;
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33 }
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34 return MP_OKAY;
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35 }
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36
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37 if ((err = mp_init_copy(&t, a)) != MP_OKAY) {
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38 return err;
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39 }
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40
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41 /* if it is negative output a - */
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42 if (t.sign == MP_NEG) {
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43 /* we have to reverse our digits later... but not the - sign!! */
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44 ++_s;
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45
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46 /* store the flag and mark the number as positive */
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47 *str++ = '-';
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48 t.sign = MP_ZPOS;
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49
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50 /* subtract a char */
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51 --maxlen;
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52 }
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53 digs = 0u;
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54 while (!MP_IS_ZERO(&t)) {
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55 if (--maxlen < 1u) {
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56 /* no more room */
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57 err = MP_BUF;
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58 goto LBL_ERR;
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59 }
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60 if ((err = mp_div_d(&t, (mp_digit)radix, &t, &d)) != MP_OKAY) {
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61 goto LBL_ERR;
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62 }
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63 *str++ = mp_s_rmap[d];
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64 ++digs;
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65 }
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66 /* reverse the digits of the string. In this case _s points
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67 * to the first digit [exluding the sign] of the number
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68 */
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69 s_mp_reverse((unsigned char *)_s, digs);
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70
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71 /* append a NULL so the string is properly terminated */
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72 *str = '\0';
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73 digs++;
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74
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75 if (written != NULL) {
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76 *written = (a->sign == MP_NEG) ? (digs + 1u): digs;
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77 }
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78
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79 LBL_ERR:
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80 mp_clear(&t);
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81 return err;
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82 }
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83
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84 #endif