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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_sign_hash.c
ECC Crypto, Tom St Denis
*/
#if defined(MECC) && defined(LTC_DER)
/**
Sign a message digest
@param in The message digest to sign
@param inlen The length of the digest
@param out [out] The destination for the signature
@param outlen [in/out] The max size and resulting size of the signature
@param prng An active PRNG state
@param wprng The index of the PRNG you wish to use
@param key A private ECC key
@return CRYPT_OK if successful
*/
int ecc_sign_hash(const unsigned char *in, unsigned long inlen,
unsigned char *out, unsigned long *outlen,
prng_state *prng, int wprng, ecc_key *key)
{
ecc_key pubkey;
void *r, *s, *e, *p;
int err;
LTC_ARGCHK(in != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
LTC_ARGCHK(key != NULL);
/* is this a private key? */
if (key->type != PK_PRIVATE) {
return CRYPT_PK_NOT_PRIVATE;
}
/* is the IDX valid ? */
if (ltc_ecc_is_valid_idx(key->idx) != 1) {
return CRYPT_PK_INVALID_TYPE;
}
if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
return err;
}
/* get the hash and load it as a bignum into 'e' */
/* init the bignums */
if ((err = mp_init_multi(&r, &s, &p, &e, NULL)) != CRYPT_OK) {
return err;
}
if ((err = mp_read_radix(p, (char *)key->dp->order, 16)) != CRYPT_OK) { goto errnokey; }
if ((err = mp_read_unsigned_bin(e, (unsigned char *)in, (int)inlen)) != CRYPT_OK) { goto errnokey; }
/* make up a key and export the public copy */
for (;;) {
if ((err = ecc_make_key_ex(prng, wprng, &pubkey, key->dp)) != CRYPT_OK) {
goto errnokey;
}
/* find r = x1 mod n */
if ((err = mp_mod(pubkey.pubkey.x, p, r)) != CRYPT_OK) { goto error; }
if (mp_iszero(r) == LTC_MP_YES) {
ecc_free(&pubkey);
} else {
/* find s = (e + xr)/k */
if ((err = mp_invmod(pubkey.k, p, pubkey.k)) != CRYPT_OK) { goto error; } /* k = 1/k */
if ((err = mp_mulmod(key->k, r, p, s)) != CRYPT_OK) { goto error; } /* s = xr */
if ((err = mp_add(e, s, s)) != CRYPT_OK) { goto error; } /* s = e + xr */
if ((err = mp_mod(s, p, s)) != CRYPT_OK) { goto error; } /* s = e + xr */
if ((err = mp_mulmod(s, pubkey.k, p, s)) != CRYPT_OK) { goto error; } /* s = (e + xr)/k */
ecc_free(&pubkey);
if (mp_iszero(s) == LTC_MP_NO) {
break;
}
}
}
/* store as SEQUENCE { r, s -- integer } */
err = der_encode_sequence_multi(out, outlen,
LTC_ASN1_INTEGER, 1UL, r,
LTC_ASN1_INTEGER, 1UL, s,
LTC_ASN1_EOL, 0UL, NULL);
goto errnokey;
error:
ecc_free(&pubkey);
errnokey:
mp_clear_multi(r, s, p, e, NULL);
return err;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_sign_hash.c,v $ */
/* $Revision: 1.9 $ */
/* $Date: 2006/12/04 02:50:11 $ */
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