1/* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 *
9 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
10 */
11#include "tomcrypt.h"
12
13/**
14  @file dsa_shared_secret.c
15  DSA Crypto, Tom St Denis
16*/
17
18#ifdef MDSA
19
20/**
21  Create a DSA shared secret between two keys
22  @param private_key      The private DSA key (the exponent)
23  @param base             The base of the exponentiation (allows this to be used for both encrypt and decrypt)
24  @param public_key       The public key
25  @param out              [out] Destination of the shared secret
26  @param outlen           [in/out] The max size and resulting size of the shared secret
27  @return CRYPT_OK if successful
28*/
29int dsa_shared_secret(void          *private_key, void *base,
30                      dsa_key       *public_key,
31                      unsigned char *out,         unsigned long *outlen)
32{
33   unsigned long  x;
34   void          *res;
35   int            err;
36
37   LTC_ARGCHK(private_key != NULL);
38   LTC_ARGCHK(public_key  != NULL);
39   LTC_ARGCHK(out         != NULL);
40   LTC_ARGCHK(outlen      != NULL);
41
42   /* make new point */
43   if ((err = mp_init(&res)) != CRYPT_OK) {
44      return err;
45   }
46
47   if ((err = mp_exptmod(base, private_key, public_key->p, res)) != CRYPT_OK) {
48      mp_clear(res);
49      return err;
50   }
51
52   x = (unsigned long)mp_unsigned_bin_size(res);
53   if (*outlen < x) {
54      *outlen = x;
55      err = CRYPT_BUFFER_OVERFLOW;
56      goto done;
57   }
58   zeromem(out, x);
59   if ((err = mp_to_unsigned_bin(res, out + (x - mp_unsigned_bin_size(res))))   != CRYPT_OK)          { goto done; }
60
61   err     = CRYPT_OK;
62   *outlen = x;
63done:
64   mp_clear(res);
65   return err;
66}
67
68#endif
69/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_shared_secret.c,v $ */
70/* $Revision: 1.7 $ */
71/* $Date: 2006/12/04 03:18:43 $ */
72
73