Mercurial > dropbear

annotate libtommath/bn_s_mp_mul_high_digs.c @ 994:5c5ade336926

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Prefer stronger algorithms in algorithm negotiation. Prefer diffie-hellman-group14-sha1 (2048 bit) over diffie-hellman-group1-sha1 (1024 bit). Due to meet-in-the-middle attacks the effective key length of three key 3DES is 112 bits. AES is stronger and faster then 3DES. Prefer to delay the start of compression until after authentication has completed. This avoids exposing compression code to attacks from unauthenticated users. (github pull request #9)
author Fedor Brunner <fedor.brunner@azet.sk>
date Fri, 23 Jan 2015 23:00:25 +0800
parents 5ff8218bcee9
children 60fc6476e044
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1 #include <tommath.h>
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2 #ifdef BN_S_MP_MUL_HIGH_DIGS_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
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4 *
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5 * LibTomMath is a library that provides multiple-precision
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6 * integer arithmetic as well as number theoretic functionality.
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7 *
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8 * The library was designed directly after the MPI library by
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9 * Michael Fromberger but has been written from scratch with
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10 * additional optimizations in place.
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11 *
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12 * The library is free for all purposes without any express
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13 * guarantee it works.
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14 *
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.com
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16 */
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17
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18 /* multiplies |a| * |b| and does not compute the lower digs digits
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19 * [meant to get the higher part of the product]
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20 */
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21 int
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22 s_mp_mul_high_digs (mp_int * a, mp_int * b, mp_int * c, int digs)
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23 {
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24 mp_int t;
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25 int res, pa, pb, ix, iy;
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26 mp_digit u;
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27 mp_word r;
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28 mp_digit tmpx, *tmpt, *tmpy;
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29
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30 /* can we use the fast multiplier? */
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31 #ifdef BN_FAST_S_MP_MUL_HIGH_DIGS_C
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32 if (((a->used + b->used + 1) < MP_WARRAY)
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33 && MIN (a->used, b->used) < (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) {
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34 return fast_s_mp_mul_high_digs (a, b, c, digs);
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35 }
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36 #endif
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37
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38 if ((res = mp_init_size (&t, a->used + b->used + 1)) != MP_OKAY) {
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39 return res;
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40 }
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41 t.used = a->used + b->used + 1;
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42
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43 pa = a->used;
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44 pb = b->used;
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45 for (ix = 0; ix < pa; ix++) {
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46 /* clear the carry */
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47 u = 0;
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48
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49 /* left hand side of A[ix] * B[iy] */
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50 tmpx = a->dp[ix];
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51
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52 /* alias to the address of where the digits will be stored */
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53 tmpt = &(t.dp[digs]);
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54
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55 /* alias for where to read the right hand side from */
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56 tmpy = b->dp + (digs - ix);
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57
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58 for (iy = digs - ix; iy < pb; iy++) {
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59 /* calculate the double precision result */
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60 r = ((mp_word)*tmpt) +
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61 ((mp_word)tmpx) * ((mp_word)*tmpy++) +
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62 ((mp_word) u);
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63
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64 /* get the lower part */
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65 *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
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66
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67 /* carry the carry */
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68 u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
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69 }
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70 *tmpt = u;
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71 }
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72 mp_clamp (&t);
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73 mp_exch (&t, c);
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74 mp_clear (&t);
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75 return MP_OKAY;
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76 }
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77 #endif
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78
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79 /* $Source: /cvs/libtom/libtommath/bn_s_mp_mul_high_digs.c,v $ */
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80 /* $Revision: 1.3 $ */
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81 /* $Date: 2006/03/31 14:18:44 $ */