rsa_v15_decrypt_key.c

	/* 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
 */

#include "mycrypt.h"

#ifdef MRSA

/* decrypt then PKCS #1 v1.5 depad  */
int rsa_v15_decrypt_key(const unsigned char *in,     unsigned long  inlen,
                              unsigned char *outkey, unsigned long keylen, 
                              prng_state    *prng,   int            prng_idx,
                              int           *res,    rsa_key       *key)
{
  unsigned long modulus_bitlen, modulus_bytelen, x;
  int           err;
  unsigned char *tmp;
  
  _ARGCHK(outkey != NULL);
  _ARGCHK(key    != NULL);
  _ARGCHK(res    != NULL);
 
  /* default to invalid */
  *res = 0;

  /* valid prng ? */
  if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
     return err;
  }
  
  /* get modulus len in bits */
  modulus_bitlen = mp_count_bits(&(key->N));

  /* outlen must be at least the size of the modulus */
  modulus_bytelen = mp_unsigned_bin_size(&(key->N));
  if (modulus_bytelen != inlen) {
     return CRYPT_INVALID_PACKET;
  }

  /* allocate ram */
  tmp = XMALLOC(inlen);
  if (tmp == NULL) {
     return CRYPT_MEM;
  }

  /* rsa decode the packet */
  x = inlen;
  if ((err = rsa_exptmod(in, inlen, tmp, &x, PK_PRIVATE, prng, prng_idx, key)) != CRYPT_OK) {
     XFREE(tmp);
     return err;
  }

  /* PKCS #1 v1.5 depad */
  err = pkcs_1_v15_es_decode(tmp, x, modulus_bitlen, outkey, keylen, res);
  XFREE(tmp);
  return err;
}

#endif