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/* 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://libtom.org
*/
#include "tomcrypt.h"
/**
@file dsa_encrypt_key.c
DSA Crypto, Tom St Denis
*/
#ifdef LTC_MDSA
/**
Encrypt a symmetric key with DSA
@param in The symmetric key you want to encrypt
@param inlen The length of the key to encrypt (octets)
@param out [out] The destination for the ciphertext
@param outlen [in/out] The max size and resulting size of the ciphertext
@param hash The index of the hash you want to use
@param key The DSA key you want to encrypt to
@return CRYPT_OK if successful
*/
int dsa_encrypt_key(const unsigned char *in, unsigned long inlen,
unsigned char *out, unsigned long *outlen,
int hash,
dsa_key *key)
{
unsigned char *expt, *skey;
void *g_pub, *g_priv;
unsigned long x, y;
int err;
LTC_ARGCHK(in != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
LTC_ARGCHK(key != NULL);
if ((err = hash_is_valid(hash)) != CRYPT_OK) {
return err;
}
if (inlen > hash_descriptor[hash].hashsize) {
return CRYPT_INVALID_HASH;
}
/* make a random key and export the public copy */
if ((err = mp_init_multi(&g_pub, &g_priv, NULL)) != CRYPT_OK) {
return err;
}
expt = XMALLOC(mp_unsigned_bin_size(key->p) + 1);
skey = XMALLOC(MAXBLOCKSIZE);
if (expt == NULL || skey == NULL) {
if (expt != NULL) {
XFREE(expt);
}
if (skey != NULL) {
XFREE(skey);
}
mp_clear_multi(g_pub, g_priv, NULL);
return CRYPT_MEM;
}
/* make a random x, g^x pair */
x = mp_unsigned_bin_size(key->q);
get_random_bytes( expt, x);
/* load x */
if ((err = mp_read_unsigned_bin(g_priv, expt, x)) != CRYPT_OK) {
goto LBL_ERR;
}
/* compute y */
if ((err = mp_exptmod(key->g, g_priv, key->p, g_pub)) != CRYPT_OK) {
goto LBL_ERR;
}
/* make random key */
x = mp_unsigned_bin_size(key->p) + 1;
if ((err = dsa_shared_secret(g_priv, key->y, key, expt, &x)) != CRYPT_OK) {
goto LBL_ERR;
}
y = MAXBLOCKSIZE;
if ((err = hash_memory(hash, expt, x, skey, &y)) != CRYPT_OK) {
goto LBL_ERR;
}
/* Encrypt key */
for (x = 0; x < inlen; x++) {
skey[x] ^= in[x];
}
err = der_encode_sequence_multi(out, outlen,
LTC_ASN1_OBJECT_IDENTIFIER, hash_descriptor[hash].OIDlen, hash_descriptor[hash].OID,
LTC_ASN1_INTEGER, 1UL, g_pub,
LTC_ASN1_OCTET_STRING, inlen, skey,
LTC_ASN1_EOL, 0UL, NULL);
LBL_ERR:
#ifdef LTC_CLEAN_STACK
/* clean up */
zeromem(expt, mp_unsigned_bin_size(key->p) + 1);
zeromem(skey, MAXBLOCKSIZE);
#endif
XFREE(skey);
XFREE(expt);
mp_clear_multi(g_pub, g_priv, NULL);
return err;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_encrypt_key.c,v $ */
/* $Revision: 1.9 $ */
/* $Date: 2007/05/12 14:32:35 $ */
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