Mercurial > dropbear

annotate libtommath/bn_mp_sqrt.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
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
284
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diff changeset
1 #include <tommath.h>
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2 #ifdef BN_MP_SQRT_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 *
389
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.com
284
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16 */
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17
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18 /* this function is less generic than mp_n_root, simpler and faster */
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19 int mp_sqrt(mp_int *arg, mp_int *ret)
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20 {
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21 int res;
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22 mp_int t1,t2;
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23
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24 /* must be positive */
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25 if (arg->sign == MP_NEG) {
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26 return MP_VAL;
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27 }
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28
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29 /* easy out */
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30 if (mp_iszero(arg) == MP_YES) {
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31 mp_zero(ret);
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32 return MP_OKAY;
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33 }
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34
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35 if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) {
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36 return res;
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37 }
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38
eed26cff980b propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583)
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39 if ((res = mp_init(&t2)) != MP_OKAY) {
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Matt Johnston <matt@ucc.asn.au>
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40 goto E2;
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41 }
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42
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43 /* First approx. (not very bad for large arg) */
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44 mp_rshd (&t1,t1.used/2);
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45
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46 /* t1 > 0 */
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47 if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
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48 goto E1;
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49 }
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50 if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
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51 goto E1;
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52 }
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53 if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
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54 goto E1;
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55 }
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56 /* And now t1 > sqrt(arg) */
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57 do {
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58 if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
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59 goto E1;
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60 }
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diff changeset
61 if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
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62 goto E1;
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63 }
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parents:
diff changeset
64 if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
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65 goto E1;
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66 }
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diff changeset
67 /* t1 >= sqrt(arg) >= t2 at this point */
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68 } while (mp_cmp_mag(&t1,&t2) == MP_GT);
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diff changeset
69
eed26cff980b propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583)
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
70 mp_exch(&t1,ret);
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Matt Johnston <matt@ucc.asn.au>
parents:
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71
eed26cff980b propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583)
Matt Johnston <matt@ucc.asn.au>
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diff changeset
72 E1: mp_clear(&t2);
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Matt Johnston <matt@ucc.asn.au>
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diff changeset
73 E2: mp_clear(&t1);
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Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
74 return res;
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Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
75 }
eed26cff980b propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583)
Matt Johnston <matt@ucc.asn.au>
parents:
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76
eed26cff980b propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583)
Matt Johnston <matt@ucc.asn.au>
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diff changeset
77 #endif
389
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parents: 284
diff changeset
78
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Matt Johnston <matt@ucc.asn.au>
parents: 284
diff changeset
79 /* $Source: /cvs/libtom/libtommath/bn_mp_sqrt.c,v $ */
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Matt Johnston <matt@ucc.asn.au>
parents: 284
diff changeset
80 /* $Revision: 1.3 $ */
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parents: 284
diff changeset
81 /* $Date: 2006/03/31 14:18:44 $ */