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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 |
