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