Mercurial > dropbear

annotate libtommath/bn_mp_exptmod.c @ 356:1085ceab122d debug-unrandom

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blah, forgot PAM options.h
author Matt Johnston <matt@ucc.asn.au>
date Wed, 09 Aug 2006 16:45:50 +0000
parents cd14c94fe89c
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
348
cd14c94fe89c add some more copious debugging
Matt Johnston <matt@ucc.asn.au>
parents: 284
diff changeset
1 #include "../dbutil.h"
284
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2 #include <tommath.h>
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3 #ifdef BN_MP_EXPTMOD_C
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4 /* LibTomMath, multiple-precision integer library -- Tom St Denis
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5 *
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6 * LibTomMath is a library that provides multiple-precision
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7 * integer arithmetic as well as number theoretic functionality.
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8 *
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9 * The library was designed directly after the MPI library by
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10 * Michael Fromberger but has been written from scratch with
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11 * additional optimizations in place.
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12 *
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13 * The library is free for all purposes without any express
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14 * guarantee it works.
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15 *
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16 * Tom St Denis, [email protected], http://math.libtomcrypt.org
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17 */
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18
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19
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20 /* this is a shell function that calls either the normal or Montgomery
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21 * exptmod functions. Originally the call to the montgomery code was
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22 * embedded in the normal function but that wasted alot of stack space
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23 * for nothing (since 99% of the time the Montgomery code would be called)
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24 */
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25 int mp_exptmod (mp_int * G, mp_int * X, mp_int * P, mp_int * Y)
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26 {
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27 int dr;
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28
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29 /* modulus P must be positive */
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30 if (P->sign == MP_NEG) {
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31 return MP_VAL;
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32 }
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33
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34 /* if exponent X is negative we have to recurse */
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35 if (X->sign == MP_NEG) {
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36 #ifdef BN_MP_INVMOD_C
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37 mp_int tmpG, tmpX;
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38 int err;
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39
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40 /* first compute 1/G mod P */
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41 if ((err = mp_init(&tmpG)) != MP_OKAY) {
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42 return err;
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43 }
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44 if ((err = mp_invmod(G, P, &tmpG)) != MP_OKAY) {
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45 mp_clear(&tmpG);
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46 return err;
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47 }
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48
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49 /* now get |X| */
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50 if ((err = mp_init(&tmpX)) != MP_OKAY) {
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51 mp_clear(&tmpG);
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52 return err;
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53 }
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54 if ((err = mp_abs(X, &tmpX)) != MP_OKAY) {
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55 mp_clear_multi(&tmpG, &tmpX, NULL);
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56 return err;
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57 }
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58
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59 /* and now compute (1/G)**|X| instead of G**X [X < 0] */
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60 err = mp_exptmod(&tmpG, &tmpX, P, Y);
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61 mp_clear_multi(&tmpG, &tmpX, NULL);
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62 return err;
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63 #else
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64 /* no invmod */
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65 return MP_VAL;
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66 #endif
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67 }
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68
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69 /* modified diminished radix reduction */
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70 #if defined(BN_MP_REDUCE_IS_2K_L_C) && defined(BN_MP_REDUCE_2K_L_C)
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71 if (mp_reduce_is_2k_l(P) == MP_YES) {
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72 return s_mp_exptmod(G, X, P, Y, 1);
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73 }
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74 #endif
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75
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76 #ifdef BN_MP_DR_IS_MODULUS_C
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77 /* is it a DR modulus? */
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78 dr = mp_dr_is_modulus(P);
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79 #else
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80 /* default to no */
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81 dr = 0;
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82 #endif
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83
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84 #ifdef BN_MP_REDUCE_IS_2K_C
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85 /* if not, is it a unrestricted DR modulus? */
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86 if (dr == 0) {
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87 dr = mp_reduce_is_2k(P) << 1;
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88 }
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89 #endif
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90
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91 /* if the modulus is odd or dr != 0 use the montgomery method */
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92 #ifdef BN_MP_EXPTMOD_FAST_C
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93 if (mp_isodd (P) == 1 || dr != 0) {
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94 return mp_exptmod_fast (G, X, P, Y, dr);
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95 } else {
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96 #endif
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97 #ifdef BN_S_MP_EXPTMOD_C
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98 /* otherwise use the generic Barrett reduction technique */
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99 return s_mp_exptmod (G, X, P, Y, 0);
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100 #else
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101 /* no exptmod for evens */
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102 return MP_VAL;
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103 #endif
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104 #ifdef BN_MP_EXPTMOD_FAST_C
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105 }
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106 #endif
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107 }
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108
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109 #endif