/* 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@iahu.ca, http://libtomcrypt.org *//* RSA Code by Tom St Denis */#include "mycrypt.h"#ifdef MRSAint rsa_exptmod(const unsigned char *in,   unsigned long inlen,                      unsigned char *out,  unsigned long *outlen, int which,                      prng_state    *prng, int           prng_idx,                      rsa_key *key){   mp_int        tmp, tmpa, tmpb;   unsigned long x;   int           err;   _ARGCHK(in     != NULL);   _ARGCHK(out    != NULL);   _ARGCHK(outlen != NULL);   _ARGCHK(key    != NULL);      if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {      return err;   }   if (which == PK_PRIVATE && (key->type != PK_PRIVATE && key->type != PK_PRIVATE_OPTIMIZED)) {      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)                     { goto error; }   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 && key->type == PK_PRIVATE_OPTIMIZED) {      /* tmpa = tmp^dP mod p */      if ((err = tim_exptmod(prng, prng_idx, &tmp, &key->e, &key->dP, &key->p, &tmpa)) != MP_OKAY)    { goto error; }      /* tmpb = tmp^dQ mod q */      if ((err = tim_exptmod(prng, prng_idx, &tmp, &key->e,  &key->dQ, &key->q, &tmpb)) != MP_OKAY)    { goto error; }      /* tmp = tmpa*qP + tmpb*pQ mod N */      if ((err = mp_mul(&tmpa, &key->qP, &tmpa)) != MP_OKAY)                { goto error; }      if ((err = mp_mul(&tmpb, &key->pQ, &tmpb)) != MP_OKAY)                { goto error; }      if ((err = mp_addmod(&tmpa, &tmpb, &key->N, &tmp)) != MP_OKAY)        { goto error; }   } else {      /* exptmod it */      if (which == PK_PRIVATE) {         if ((err = tim_exptmod(prng, prng_idx, &tmp, &key->e, &key->d, &key->N, &tmp)) != MP_OKAY) { goto error; }      } else {         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;   }   *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