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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.org
*/
#include "tomcrypt.h"
/**
@file dsa_sign_hash.c
DSA implementation, sign a hash, Tom St Denis
*/
#ifdef MDSA
/**
Sign a hash with DSA
@param in The hash to sign
@param inlen The length of the hash to sign
@param r The "r" integer of the signature (caller must initialize with mp_init() first)
@param s The "s" integer of the signature (caller must initialize with mp_init() first)
@param prng An active PRNG state
@param wprng The index of the PRNG desired
@param key A private DSA key
@return CRYPT_OK if successful
*/
int dsa_sign_hash_raw(const unsigned char *in, unsigned long inlen,
mp_int *r, mp_int *s,
prng_state *prng, int wprng, dsa_key *key)
{
mp_int k, kinv, tmp;
unsigned char *buf;
int err;
LTC_ARGCHK(in != NULL);
LTC_ARGCHK(r != NULL);
LTC_ARGCHK(s != NULL);
LTC_ARGCHK(key != NULL);
if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
return err;
}
if (key->type != PK_PRIVATE) {
return CRYPT_PK_NOT_PRIVATE;
}
/* check group order size */
if (key->qord >= MDSA_MAX_GROUP) {
return CRYPT_INVALID_ARG;
}
buf = XMALLOC(MDSA_MAX_GROUP);
if (buf == NULL) {
return CRYPT_MEM;
}
/* Init our temps */
if ((err = mp_init_multi(&k, &kinv, &tmp, NULL)) != MP_OKAY) { goto error; }
retry:
do {
/* gen random k */
if (prng_descriptor[wprng].read(buf, key->qord, prng) != (unsigned long)key->qord) {
err = CRYPT_ERROR_READPRNG;
goto LBL_ERR;
}
/* read k */
if ((err = mp_read_unsigned_bin(&k, buf, key->qord)) != MP_OKAY) { goto error; }
/* k > 1 ? */
if (mp_cmp_d(&k, 1) != MP_GT) { goto retry; }
/* test gcd */
if ((err = mp_gcd(&k, &key->q, &tmp)) != MP_OKAY) { goto error; }
} while (mp_cmp_d(&tmp, 1) != MP_EQ);
/* now find 1/k mod q */
if ((err = mp_invmod(&k, &key->q, &kinv)) != MP_OKAY) { goto error; }
/* now find r = g^k mod p mod q */
if ((err = mp_exptmod(&key->g, &k, &key->p, r)) != MP_OKAY) { goto error; }
if ((err = mp_mod(r, &key->q, r)) != MP_OKAY) { goto error; }
if (mp_iszero(r) == MP_YES) { goto retry; }
/* now find s = (in + xr)/k mod q */
if ((err = mp_read_unsigned_bin(&tmp, (unsigned char *)in, inlen)) != MP_OKAY) { goto error; }
if ((err = mp_mul(&key->x, r, s)) != MP_OKAY) { goto error; }
if ((err = mp_add(s, &tmp, s)) != MP_OKAY) { goto error; }
if ((err = mp_mulmod(s, &kinv, &key->q, s)) != MP_OKAY) { goto error; }
if (mp_iszero(s) == MP_YES) { goto retry; }
err = CRYPT_OK;
goto LBL_ERR;
error:
err = mpi_to_ltc_error(err);
LBL_ERR:
mp_clear_multi(&k, &kinv, &tmp, NULL);
#ifdef LTC_CLEAN_STACK
zeromem(buf, MDSA_MAX_GROUP);
#endif
XFREE(buf);
return err;
}
/**
Sign a hash with DSA
@param in The hash to sign
@param inlen The length of the hash to sign
@param out [out] Where to store 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 desired
@param key A private DSA key
@return CRYPT_OK if successful
*/
int dsa_sign_hash(const unsigned char *in, unsigned long inlen,
unsigned char *out, unsigned long *outlen,
prng_state *prng, int wprng, dsa_key *key)
{
mp_int r, s;
int err;
LTC_ARGCHK(in != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
LTC_ARGCHK(key != NULL);
if (mp_init_multi(&r, &s, NULL) != MP_OKAY) {
return CRYPT_MEM;
}
if ((err = dsa_sign_hash_raw(in, inlen, &r, &s, prng, wprng, key)) != CRYPT_OK) {
goto LBL_ERR;
}
err = der_encode_sequence_multi(out, outlen,
LTC_ASN1_INTEGER, 1UL, &r,
LTC_ASN1_INTEGER, 1UL, &s,
LTC_ASN1_EOL, 0UL, NULL);
LBL_ERR:
mp_clear_multi(&r, &s, NULL);
return err;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_sign_hash.c,v $ */
/* $Revision: 1.6 $ */
/* $Date: 2005/05/15 21:48:59 $ */
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