Mercurial > dropbear
annotate libtommath/bn_mp_exptmod.c @ 1861:2b3a8026a6ce
Add re-exec for server
This allows ASLR to re-randomize the address
space for every connection, preventing some
vulnerabilities from being exploitable by
repeated probing.
Overhead (memory and time) is yet to be confirmed.
At present this is only enabled on Linux. Other BSD platforms
with fexecve() would probably also work though have not been tested.
author | Matt Johnston <matt@ucc.asn.au> |
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date | Sun, 30 Jan 2022 10:14:56 +0800 |
parents | 1051e4eea25a |
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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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5 |
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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 |