/* 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 */#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){   void         *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)) != CRYPT_OK)                                    { return err; }   if ((err = mp_read_unsigned_bin(tmp, (unsigned char *)in, (int)inlen)) != CRYPT_OK)                 { goto error; }   /* sanity check on the input */   if (mp_cmp(key->N, tmp) == LTC_MP_LT) {      err = CRYPT_PK_INVALID_SIZE;      goto error;   }   /* 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)) != CRYPT_OK)                               { goto error; }      /* tmpb = tmp^dQ mod q */      if ((err = mp_exptmod(tmp, key->dQ, key->q, tmpb)) != CRYPT_OK)                               { goto error; }      /* tmp = (tmpa - tmpb) * qInv (mod p) */      if ((err = mp_sub(tmpa, tmpb, tmp)) != CRYPT_OK)                                              { goto error; }      if ((err = mp_mulmod(tmp, key->qP, key->p, tmp)) != CRYPT_OK)                                { goto error; }      /* tmp = tmpb + q * tmp */      if ((err = mp_mul(tmp, key->q, tmp)) != CRYPT_OK)                                             { goto error; }      if ((err = mp_add(tmp, tmpb, tmp)) != CRYPT_OK)                                               { goto error; }   } else {      /* exptmod it */      if ((err = mp_exptmod(tmp, key->e, key->N, tmp)) != CRYPT_OK)                                { goto error; }   }   /* read it back */   x = (unsigned long)mp_unsigned_bin_size(key->N);   if (x > *outlen) {      *outlen = x;      err = CRYPT_BUFFER_OVERFLOW;      goto error;   }   /* this should never happen ... */   if (mp_unsigned_bin_size(tmp) > mp_unsigned_bin_size(key->N)) {      err = CRYPT_ERROR;      goto error;   }   *outlen = x;   /* convert it */   zeromem(out, x);   if ((err = mp_to_unsigned_bin(tmp, out+(x-mp_unsigned_bin_size(tmp)))) != CRYPT_OK)               { goto error; }   /* clean up and return */   err = CRYPT_OK;error:   mp_clear_multi(tmp, tmpa, tmpb, NULL);   return err;}#endif/* $Source: /cvs/libtom/libtomcrypt/src/pk/rsa/rsa_exptmod.c,v $ *//* $Revision: 1.16 $ *//* $Date: 2006/12/04 03:09:28 $ */