Mercurial > dropbear
annotate bn_mp_exptmod.c @ 201:c0bf626ee437 libtommath
Bringing back the original ltc 0.35 makefile
| author | Matt Johnston <matt@ucc.asn.au> |
|---|---|
| date | Wed, 11 May 2005 16:23:24 +0000 |
| parents | c5c969ed76f3 |
| children |
| rev | line source |
|---|---|
| 142 | 1 #include <tommath.h> |
| 2 #ifdef BN_MP_EXPTMOD_C | |
| 1 | 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis |
| 4 * | |
| 5 * LibTomMath is a library that provides multiple-precision | |
| 6 * integer arithmetic as well as number theoretic functionality. | |
| 7 * | |
| 8 * The library was designed directly after the MPI library by | |
| 9 * Michael Fromberger but has been written from scratch with | |
| 10 * additional optimizations in place. | |
| 11 * | |
| 12 * The library is free for all purposes without any express | |
| 13 * guarantee it works. | |
| 14 * | |
| 15 * Tom St Denis, [email protected], http://math.libtomcrypt.org | |
| 16 */ | |
| 17 | |
| 18 | |
| 19 /* this is a shell function that calls either the normal or Montgomery | |
| 20 * exptmod functions. Originally the call to the montgomery code was | |
| 21 * embedded in the normal function but that wasted alot of stack space | |
| 22 * for nothing (since 99% of the time the Montgomery code would be called) | |
| 23 */ | |
| 24 int mp_exptmod (mp_int * G, mp_int * X, mp_int * P, mp_int * Y) | |
| 25 { | |
| 26 int dr; | |
| 27 | |
| 28 /* modulus P must be positive */ | |
| 29 if (P->sign == MP_NEG) { | |
| 30 return MP_VAL; | |
| 31 } | |
| 32 | |
| 33 /* if exponent X is negative we have to recurse */ | |
| 34 if (X->sign == MP_NEG) { | |
| 142 | 35 #ifdef BN_MP_INVMOD_C |
| 1 | 36 mp_int tmpG, tmpX; |
| 37 int err; | |
| 38 | |
| 39 /* first compute 1/G mod P */ | |
| 40 if ((err = mp_init(&tmpG)) != MP_OKAY) { | |
| 41 return err; | |
| 42 } | |
| 43 if ((err = mp_invmod(G, P, &tmpG)) != MP_OKAY) { | |
| 44 mp_clear(&tmpG); | |
| 45 return err; | |
| 46 } | |
| 47 | |
| 48 /* now get |X| */ | |
| 49 if ((err = mp_init(&tmpX)) != MP_OKAY) { | |
| 50 mp_clear(&tmpG); | |
| 51 return err; | |
| 52 } | |
| 53 if ((err = mp_abs(X, &tmpX)) != MP_OKAY) { | |
| 54 mp_clear_multi(&tmpG, &tmpX, NULL); | |
| 55 return err; | |
| 56 } | |
| 57 | |
| 58 /* and now compute (1/G)**|X| instead of G**X [X < 0] */ | |
| 59 err = mp_exptmod(&tmpG, &tmpX, P, Y); | |
| 60 mp_clear_multi(&tmpG, &tmpX, NULL); | |
| 61 return err; | |
| 142 | 62 #else |
| 63 /* no invmod */ | |
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64 return MP_VAL; |
| 142 | 65 #endif |
| 1 | 66 } |
| 67 | |
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68 /* modified diminished radix reduction */ |
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69 #if defined(BN_MP_REDUCE_IS_2K_L_C) && defined(BN_MP_REDUCE_2K_L_C) |
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70 if (mp_reduce_is_2k_l(P) == MP_YES) { |
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71 return s_mp_exptmod(G, X, P, Y, 1); |
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72 } |
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73 #endif |
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74 |
| 142 | 75 #ifdef BN_MP_DR_IS_MODULUS_C |
| 1 | 76 /* is it a DR modulus? */ |
| 77 dr = mp_dr_is_modulus(P); | |
| 142 | 78 #else |
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79 /* default to no */ |
| 142 | 80 dr = 0; |
| 81 #endif | |
| 1 | 82 |
| 142 | 83 #ifdef BN_MP_REDUCE_IS_2K_C |
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84 /* if not, is it a unrestricted DR modulus? */ |
| 1 | 85 if (dr == 0) { |
| 86 dr = mp_reduce_is_2k(P) << 1; | |
| 87 } | |
| 142 | 88 #endif |
| 1 | 89 |
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90 /* if the modulus is odd or dr != 0 use the montgomery method */ |
| 142 | 91 #ifdef BN_MP_EXPTMOD_FAST_C |
| 1 | 92 if (mp_isodd (P) == 1 || dr != 0) { |
| 93 return mp_exptmod_fast (G, X, P, Y, dr); | |
| 2 | 94 } else { |
| 1 | 95 #endif |
| 142 | 96 #ifdef BN_S_MP_EXPTMOD_C |
| 1 | 97 /* otherwise use the generic Barrett reduction technique */ |
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98 return s_mp_exptmod (G, X, P, Y, 0); |
| 142 | 99 #else |
| 100 /* no exptmod for evens */ | |
| 101 return MP_VAL; | |
| 102 #endif | |
| 103 #ifdef BN_MP_EXPTMOD_FAST_C | |
| 1 | 104 } |
| 142 | 105 #endif |
| 1 | 106 } |
| 107 | |
| 142 | 108 #endif |