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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 rsa_exptmod.c
RSA PKCS exptmod, Tom St Denis
*/
#ifdef MRSA
/**
Compute an RSA modular exponentiation
@param in The input data to send into RSA
@param inlen The length of the input (octets)
@param out [out] The destination
@param outlen [in/out] The max size and resulting size of the output
@param which Which exponent to use, e.g. PK_PRIVATE or PK_PUBLIC
@param key The RSA key to use
@return CRYPT_OK if successful
*/
int rsa_exptmod(const unsigned char *in, unsigned long inlen,
unsigned char *out, unsigned long *outlen, int which,
rsa_key *key)
{
mp_int tmp, tmpa, tmpb;
unsigned long x;
int err;
LTC_ARGCHK(in != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
LTC_ARGCHK(key != NULL);
/* is the key of the right type for the operation? */
if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) {
return CRYPT_PK_NOT_PRIVATE;
}
/* must be a private or public operation */
if (which != PK_PRIVATE && which != PK_PUBLIC) {
return CRYPT_PK_INVALID_TYPE;
}
/* init and copy into tmp */
if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != MP_OKAY) { return mpi_to_ltc_error(err); }
if ((err = mp_read_unsigned_bin(&tmp, (unsigned char *)in, (int)inlen)) != MP_OKAY) { goto error; }
/* sanity check on the input */
if (mp_cmp(&key->N, &tmp) == MP_LT) {
err = CRYPT_PK_INVALID_SIZE;
goto done;
}
/* are we using the private exponent and is the key optimized? */
if (which == PK_PRIVATE) {
/* tmpa = tmp^dP mod p */
if ((err = mp_exptmod(&tmp, &key->dP, &key->p, &tmpa)) != MP_OKAY) { goto error; }
/* tmpb = tmp^dQ mod q */
if ((err = mp_exptmod(&tmp, &key->dQ, &key->q, &tmpb)) != MP_OKAY) { goto error; }
/* tmp = (tmpa - tmpb) * qInv (mod p) */
if ((err = mp_sub(&tmpa, &tmpb, &tmp)) != MP_OKAY) { goto error; }
if ((err = mp_mulmod(&tmp, &key->qP, &key->p, &tmp)) != MP_OKAY) { goto error; }
/* tmp = tmpb + q * tmp */
if ((err = mp_mul(&tmp, &key->q, &tmp)) != MP_OKAY) { goto error; }
if ((err = mp_add(&tmp, &tmpb, &tmp)) != MP_OKAY) { goto error; }
} else {
/* exptmod it */
if ((err = mp_exptmod(&tmp, &key->e, &key->N, &tmp)) != MP_OKAY) { goto error; }
}
/* read it back */
x = (unsigned long)mp_unsigned_bin_size(&key->N);
if (x > *outlen) {
err = CRYPT_BUFFER_OVERFLOW;
goto done;
}
/* this should never happen ... */
if (mp_unsigned_bin_size(&tmp) > mp_unsigned_bin_size(&key->N)) {
err = CRYPT_ERROR;
goto done;
}
*outlen = x;
/* convert it */
zeromem(out, x);
if ((err = mp_to_unsigned_bin(&tmp, out+(x-mp_unsigned_bin_size(&tmp)))) != MP_OKAY) { goto error; }
/* clean up and return */
err = CRYPT_OK;
goto done;
error:
err = mpi_to_ltc_error(err);
done:
mp_clear_multi(&tmp, &tmpa, &tmpb, NULL);
return err;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/rsa/rsa_exptmod.c,v $ */
/* $Revision: 1.4 $ */
/* $Date: 2005/06/23 02:10:22 $ */
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