| /* 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 $ */ |
| |