/* LibTomCrypt, modular cryptographic library -- Tom St Denis * * LibTomCrypt is a library that provides various cryptographic * algorithms in a highly modular and flexible manner. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com */#include "tomcrypt.h"/**  @file dsa_shared_secret.c  DSA Crypto, Tom St Denis*/  #ifdef MDSA/**  Create a DSA shared secret between two keys  @param private_key      The private DSA key (the exponent)  @param base             The base of the exponentiation (allows this to be used for both encrypt and decrypt)   @param public_key       The public key  @param out              [out] Destination of the shared secret  @param outlen           [in/out] The max size and resulting size of the shared secret  @return CRYPT_OK if successful*/int dsa_shared_secret(void          *private_key, void *base,                      dsa_key       *public_key,                      unsigned char *out,         unsigned long *outlen){   unsigned long  x;   void          *res;   int            err;   LTC_ARGCHK(private_key != NULL);   LTC_ARGCHK(public_key  != NULL);   LTC_ARGCHK(out         != NULL);   LTC_ARGCHK(outlen      != NULL);   /* make new point */   if ((err = mp_init(&res)) != CRYPT_OK) {      return err;   }   if ((err = mp_exptmod(base, private_key, public_key->p, res)) != CRYPT_OK) {      mp_clear(res);      return err;   }      x = (unsigned long)mp_unsigned_bin_size(res);   if (*outlen < x) {      *outlen = x;      err = CRYPT_BUFFER_OVERFLOW;      goto done;   }   zeromem(out, x);   if ((err = mp_to_unsigned_bin(res, out + (x - mp_unsigned_bin_size(res))))   != CRYPT_OK)          { goto done; }   err     = CRYPT_OK;   *outlen = x;done:   mp_clear(res);   return err;}#endif/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_shared_secret.c,v $ *//* $Revision: 1.7 $ *//* $Date: 2006/12/04 03:18:43 $ */