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annotate libtomcrypt/src/pk/dh/dh_shared_secret.c @ 1729:f091f7536aa5

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Refer to libtom license files
author Matt Johnston <matt@ucc.asn.au>
date Thu, 25 Jun 2020 23:18:16 +0800
parents 6dba84798cd5
children
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rev   line source
1471
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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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
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10 #include "tomcrypt.h"
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11
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12 #ifdef LTC_MDH
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13
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14 /**
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15 Create a DH shared secret.
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16 @param private_key The private DH key in the pair
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17 @param public_key The public DH key in the pair
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18 @param out [out] The destination of the shared data
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19 @param outlen [in/out] The max size and resulting size of the shared data.
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20 @return CRYPT_OK if successful
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21 */
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22 int dh_shared_secret(dh_key *private_key, dh_key *public_key,
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23 unsigned char *out, unsigned long *outlen)
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24 {
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25 void *tmp;
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26 unsigned long x;
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27 int err;
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28
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29 LTC_ARGCHK(private_key != NULL);
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30 LTC_ARGCHK(public_key != NULL);
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31 LTC_ARGCHK(out != NULL);
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32 LTC_ARGCHK(outlen != NULL);
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33
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34 /* types valid? */
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35 if (private_key->type != PK_PRIVATE) {
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36 return CRYPT_PK_NOT_PRIVATE;
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37 }
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38
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39 /* same DH group? */
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40 if (mp_cmp(private_key->prime, public_key->prime) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; }
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41 if (mp_cmp(private_key->base, public_key->base) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; }
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42
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43 /* init big numbers */
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44 if ((err = mp_init(&tmp)) != CRYPT_OK) {
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45 return err;
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46 }
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47
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48 /* check public key */
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49 if ((err = dh_check_pubkey(public_key)) != CRYPT_OK) {
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50 goto error;
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51 }
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52
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53 /* compute tmp = y^x mod p */
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54 if ((err = mp_exptmod(public_key->y, private_key->x, private_key->prime, tmp)) != CRYPT_OK) {
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55 goto error;
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56 }
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57
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58 /* enough space for output? */
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59 x = (unsigned long)mp_unsigned_bin_size(tmp);
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60 if (*outlen < x) {
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61 *outlen = x;
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62 err = CRYPT_BUFFER_OVERFLOW;
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63 goto error;
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64 }
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65 if ((err = mp_to_unsigned_bin(tmp, out)) != CRYPT_OK) {
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66 goto error;
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67 }
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68 *outlen = x;
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69 err = CRYPT_OK;
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70
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71 error:
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72 mp_clear(tmp);
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73 return err;
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74 }
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75
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76 #endif /* LTC_MDH */
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77
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78 /* ref: $Format:%D$ */
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79 /* git commit: $Format:%H$ */
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80 /* commit time: $Format:%ai$ */