Mercurial > dropbear

annotate libtomcrypt/src/pk/dsa/dsa_shared_secret.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 0cbe8f6dbf9e
children f849a5ca2efc
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
382
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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
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2 *
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3 * LibTomCrypt is a library that provides various cryptographic
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4 * algorithms in a highly modular and flexible manner.
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5 *
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6 * The library is free for all purposes without any express
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7 * guarantee it works.
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8 *
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9 * Tom St Denis, [email protected], http://libtomcrypt.com
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10 */
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11 #include "tomcrypt.h"
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12
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13 /**
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14 @file dsa_shared_secret.c
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15 DSA Crypto, Tom St Denis
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16 */
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17
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18 #ifdef MDSA
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19
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20 /**
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21 Create a DSA shared secret between two keys
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22 @param private_key The private DSA key (the exponent)
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23 @param base The base of the exponentiation (allows this to be used for both encrypt and decrypt)
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24 @param public_key The public key
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25 @param out [out] Destination of the shared secret
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26 @param outlen [in/out] The max size and resulting size of the shared secret
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27 @return CRYPT_OK if successful
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28 */
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29 int dsa_shared_secret(void *private_key, void *base,
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30 dsa_key *public_key,
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31 unsigned char *out, unsigned long *outlen)
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32 {
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33 unsigned long x;
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34 void *res;
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35 int err;
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36
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37 LTC_ARGCHK(private_key != NULL);
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38 LTC_ARGCHK(public_key != NULL);
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39 LTC_ARGCHK(out != NULL);
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40 LTC_ARGCHK(outlen != NULL);
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41
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42 /* make new point */
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43 if ((err = mp_init(&res)) != CRYPT_OK) {
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44 return err;
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45 }
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46
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47 if ((err = mp_exptmod(base, private_key, public_key->p, res)) != CRYPT_OK) {
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48 mp_clear(res);
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49 return err;
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50 }
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51
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52 x = (unsigned long)mp_unsigned_bin_size(res);
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53 if (*outlen < x) {
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54 *outlen = x;
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55 err = CRYPT_BUFFER_OVERFLOW;
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56 goto done;
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57 }
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58 zeromem(out, x);
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59 if ((err = mp_to_unsigned_bin(res, out + (x - mp_unsigned_bin_size(res)))) != CRYPT_OK) { goto done; }
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60
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61 err = CRYPT_OK;
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62 *outlen = x;
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63 done:
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64 mp_clear(res);
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65 return err;
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66 }
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67
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68 #endif
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69 /* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_shared_secret.c,v $ */
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70 /* $Revision: 1.7 $ */
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71 /* $Date: 2006/12/04 03:18:43 $ */
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72