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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://libtomcrypt.com
*/
/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
*
* All curves taken from NIST recommendation paper of July 1999
* Available at http://csrc.nist.gov/cryptval/dss.htm
*/
#include "tomcrypt.h"
/**
@file ecc_decrypt_key.c
ECC Crypto, Tom St Denis
*/
#if defined(MECC) && defined(LTC_DER)
/**
Decrypt an ECC 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 ECC key
@return CRYPT_OK if successful
*/
int ecc_decrypt_key(const unsigned char *in, unsigned long inlen,
unsigned char *out, unsigned long *outlen,
ecc_key *key)
{
unsigned char *ecc_shared, *skey, *pub_expt;
unsigned long x, y, hashOID[32];
int hash, err;
ecc_key pubkey;
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! */
/* allocate memory */
pub_expt = XMALLOC(ECC_BUF_SIZE);
ecc_shared = XMALLOC(ECC_BUF_SIZE);
skey = XMALLOC(MAXBLOCKSIZE);
if (pub_expt == NULL || ecc_shared == NULL || skey == NULL) {
if (pub_expt != NULL) {
XFREE(pub_expt);
}
if (ecc_shared != NULL) {
XFREE(ecc_shared);
}
if (skey != NULL) {
XFREE(skey);
}
return CRYPT_MEM;
}
LTC_SET_ASN1(decode, 1, LTC_ASN1_OCTET_STRING, pub_expt, ECC_BUF_SIZE);
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;
}
/* import ECC key from packet */
if ((err = ecc_import(decode[1].data, decode[1].size, &pubkey)) != CRYPT_OK) {
goto LBL_ERR;
}
/* make shared key */
x = ECC_BUF_SIZE;
if ((err = ecc_shared_secret(key, &pubkey, ecc_shared, &x)) != CRYPT_OK) {
ecc_free(&pubkey);
goto LBL_ERR;
}
ecc_free(&pubkey);
y = MIN(ECC_BUF_SIZE, MAXBLOCKSIZE);
if ((err = hash_memory(hash, ecc_shared, x, ecc_shared, &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] = skey[x] ^ ecc_shared[x];
}
*outlen = x;
err = CRYPT_OK;
LBL_ERR:
#ifdef LTC_CLEAN_STACK
zeromem(pub_expt, ECC_BUF_SIZE);
zeromem(ecc_shared, ECC_BUF_SIZE);
zeromem(skey, MAXBLOCKSIZE);
#endif
XFREE(pub_expt);
XFREE(ecc_shared);
XFREE(skey);
return err;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_decrypt_key.c,v $ */
/* $Revision: 1.5 $ */
/* $Date: 2006/06/16 21:53:41 $ */
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