Mercurial > dropbear

annotate libtommath/bn_mp_exptmod.c @ 1857:6022df862942

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Use DSCP for IP QoS traffic classes The previous TOS values are deprecated and not used by modern traffic classifiers. This sets AF21 for "interactive" traffic (with a tty). Non-tty traffic sets AF11 - that indicates high throughput but is not lowest priority (which would be CS1 or LE). This differs from the CS1 used by OpenSSH, it lets interactive git over SSH have higher priority than background least effort traffic. Dropbear's settings here should be suitable with the diffservs used by CAKE qdisc.
author Matt Johnston <matt@ucc.asn.au>
date Tue, 25 Jan 2022 17:32:20 +0800
parents 1051e4eea25a
children
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_EXPTMOD_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 /* this is a shell function that calls either the normal or Montgomery
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7 * exptmod functions. Originally the call to the montgomery code was
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8 * embedded in the normal function but that wasted alot of stack space
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9 * for nothing (since 99% of the time the Montgomery code would be called)
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10 */
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11 mp_err mp_exptmod(const mp_int *G, const mp_int *X, const mp_int *P, mp_int *Y)
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12 {
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13 int dr;
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14
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15 /* modulus P must be positive */
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16 if (P->sign == MP_NEG) {
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17 return MP_VAL;
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18 }
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19
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20 /* if exponent X is negative we have to recurse */
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21 if (X->sign == MP_NEG) {
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22 mp_int tmpG, tmpX;
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23 mp_err err;
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24
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25 if (!MP_HAS(MP_INVMOD)) {
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26 return MP_VAL;
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27 }
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28
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29 if ((err = mp_init_multi(&tmpG, &tmpX, NULL)) != MP_OKAY) {
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30 return err;
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31 }
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32
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33 /* first compute 1/G mod P */
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34 if ((err = mp_invmod(G, P, &tmpG)) != MP_OKAY) {
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35 goto LBL_ERR;
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36 }
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37
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38 /* now get |X| */
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39 if ((err = mp_abs(X, &tmpX)) != MP_OKAY) {
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40 goto LBL_ERR;
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41 }
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42
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43 /* and now compute (1/G)**|X| instead of G**X [X < 0] */
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44 err = mp_exptmod(&tmpG, &tmpX, P, Y);
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45 LBL_ERR:
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46 mp_clear_multi(&tmpG, &tmpX, NULL);
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47 return err;
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48 }
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49
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50 /* modified diminished radix reduction */
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51 if (MP_HAS(MP_REDUCE_IS_2K_L) && MP_HAS(MP_REDUCE_2K_L) && MP_HAS(S_MP_EXPTMOD) &&
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52 (mp_reduce_is_2k_l(P) == MP_YES)) {
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53 return s_mp_exptmod(G, X, P, Y, 1);
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54 }
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55
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56 /* is it a DR modulus? default to no */
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57 dr = (MP_HAS(MP_DR_IS_MODULUS) && (mp_dr_is_modulus(P) == MP_YES)) ? 1 : 0;
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58
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59 /* if not, is it a unrestricted DR modulus? */
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60 if (MP_HAS(MP_REDUCE_IS_2K) && (dr == 0)) {
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61 dr = (mp_reduce_is_2k(P) == MP_YES) ? 2 : 0;
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62 }
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63
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64 /* if the modulus is odd or dr != 0 use the montgomery method */
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65 if (MP_HAS(S_MP_EXPTMOD_FAST) && (MP_IS_ODD(P) || (dr != 0))) {
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66 return s_mp_exptmod_fast(G, X, P, Y, dr);
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67 } else if (MP_HAS(S_MP_EXPTMOD)) {
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68 /* otherwise use the generic Barrett reduction technique */
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69 return s_mp_exptmod(G, X, P, Y, 0);
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70 } else {
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71 /* no exptmod for evens */
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72 return MP_VAL;
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73 }
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74 }
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75
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76 #endif