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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_decrypt_key.c
DSA Crypto, Tom St Denis
*/
#ifdef LTC_MDSA
/**
Decrypt an DSA encrypted key
@param in The ciphertext
@param inlen The length of the ciphertext (octets)
@param out [out] The plaintext
@param outlen [in/out] The max size and resulting size of the plaintext
@param key The corresponding private DSA key
@return CRYPT_OK if successful
*/
int dsa_decrypt_key(const unsigned char *in, unsigned long inlen,
unsigned char *out, unsigned long *outlen,
dsa_key *key)
{
unsigned char *skey, *expt;
void *g_pub;
unsigned long x, y, hashOID[32];
int hash, err;
ltc_asn1_list decode[3];
LTC_ARGCHK(in != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
LTC_ARGCHK(key != NULL);
/* right key type? */
if (key->type != PK_PRIVATE) {
return CRYPT_PK_NOT_PRIVATE;
}
/* decode to find out hash */
LTC_SET_ASN1(decode, 0, LTC_ASN1_OBJECT_IDENTIFIER, hashOID, sizeof(hashOID)/sizeof(hashOID[0]));
if ((err = der_decode_sequence(in, inlen, decode, 1)) != CRYPT_OK) {
return err;
}
hash = find_hash_oid(hashOID, decode[0].size);
if (hash_is_valid(hash) != CRYPT_OK) {
return CRYPT_INVALID_PACKET;
}
/* we now have the hash! */
if ((err = mp_init(&g_pub)) != CRYPT_OK) {
return err;
}
/* allocate memory */
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(g_pub);
return CRYPT_MEM;
}
LTC_SET_ASN1(decode, 1, LTC_ASN1_INTEGER, g_pub, 1UL);
LTC_SET_ASN1(decode, 2, LTC_ASN1_OCTET_STRING, skey, MAXBLOCKSIZE);
/* read the structure in now */
if ((err = der_decode_sequence(in, inlen, decode, 3)) != CRYPT_OK) {
goto LBL_ERR;
}
/* make shared key */
x = mp_unsigned_bin_size(key->p) + 1;
if ((err = dsa_shared_secret(key->x, g_pub, key, expt, &x)) != CRYPT_OK) {
goto LBL_ERR;
}
y = MIN(mp_unsigned_bin_size(key->p) + 1, MAXBLOCKSIZE);
if ((err = hash_memory(hash, expt, x, expt, &y)) != CRYPT_OK) {
goto LBL_ERR;
}
/* ensure the hash of the shared secret is at least as big as the encrypt itself */
if (decode[2].size > y) {
err = CRYPT_INVALID_PACKET;
goto LBL_ERR;
}
/* avoid buffer overflow */
if (*outlen < decode[2].size) {
*outlen = decode[2].size;
err = CRYPT_BUFFER_OVERFLOW;
goto LBL_ERR;
}
/* Decrypt the key */
for (x = 0; x < decode[2].size; x++) {
out[x] = expt[x] ^ skey[x];
}
*outlen = x;
err = CRYPT_OK;
LBL_ERR:
#ifdef LTC_CLEAN_STACK
zeromem(expt, mp_unsigned_bin_size(key->p) + 1);
zeromem(skey, MAXBLOCKSIZE);
#endif
XFREE(expt);
XFREE(skey);
mp_clear(g_pub);
return err;
}
#endif
/* $Source$ */
/* $Revision$ */
/* $Date$ */
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