/* 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 RSA_TIMING/* decrypts c into m */int tim_exptmod(prng_state *prng, int prng_idx,                 mp_int *c, mp_int *e, mp_int *d, mp_int *n, mp_int *m){   int           err;   mp_int        r, tmp, tmp2;   unsigned char *rtmp;   unsigned long rlen;   _ARGCHK(c != NULL);   _ARGCHK(e != NULL);   _ARGCHK(d != NULL);   _ARGCHK(n != NULL);   _ARGCHK(m != NULL);   if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {      return err;   }   /* pick random r */    rtmp = XMALLOC(MAX_RSA_SIZE/8);   if (rtmp == NULL) {      return CRYPT_MEM;   }   rlen = mp_unsigned_bin_size(n);   if (prng_descriptor[prng_idx].read(rtmp, rlen, prng) != rlen) {      XFREE(rtmp);      return CRYPT_ERROR_READPRNG;   }   if ((err = mp_init_multi(&r, &tmp, &tmp2, NULL)) != MP_OKAY) {      XFREE(rtmp);      return mpi_to_ltc_error(err);   }   /* read in r */   if ((err = mp_read_unsigned_bin(&r, rtmp, rlen)) != MP_OKAY)              { goto __ERR; }   /* compute tmp = r^e */   if ((err = mp_exptmod(&r, e, n, &tmp)) != MP_OKAY)                        { goto __ERR; }   /* multiply C into the mix */   if ((err = mp_mulmod(c, &tmp, n, &tmp)) != MP_OKAY)                       { goto __ERR; }   /* raise to d */   if ((err = mp_exptmod(&tmp, d, n, &tmp)) != MP_OKAY)                      { goto __ERR; }      /* invert r and multiply */   if ((err = mp_invmod(&r, n, &tmp2)) != MP_OKAY)                           { goto __ERR; }   /* multiply and we are totally set */   if ((err = mp_mulmod(&tmp, &tmp2, n, m)) != MP_OKAY)                      { goto __ERR; }__ERR:  mp_clear_multi(&r, &tmp, &tmp2, NULL);   XFREE(rtmp);   return mpi_to_ltc_error(err);}#endif