/**
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 prng An active PRNG state
@param wprng The index of the PRNG you wish to use
@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,
prng_state *prng, int wprng, 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);
/* check that wprng/cipher/hash are not invalid */
if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
return err;
}
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 g_priv, g_pub = g^x pair
private key x should be in range: 1 <= x <= q-1 (see FIPS 186-4 B.1.2)
*/
if ((err = rand_bn_upto(g_priv, key->q, prng, wprng)) != 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;
}
/**
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;
}
