pkcs_1_i2osp.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.
 */
#include "tomcrypt.h"

/**
  @file pkcs_1_i2osp.c
  Integer to Octet I2OSP, Tom St Denis
*/

#ifdef LTC_PKCS_1

/* always stores the same # of bytes, pads with leading zero bytes
   as required
 */

/**
   PKCS #1 Integer to binary
   @param n             The integer to store
   @param modulus_len   The length of the RSA modulus
   @param out           [out] The destination for the integer
   @return CRYPT_OK if successful
*/
int pkcs_1_i2osp(void *n, unsigned long modulus_len, unsigned char *out)
{
   unsigned long size;

   size = mp_unsigned_bin_size(n);

   if (size > modulus_len) {
      return CRYPT_BUFFER_OVERFLOW;
   }

   /* store it */
   zeromem(out, modulus_len);
   return mp_to_unsigned_bin(n, out+(modulus_len-size));
}

#endif /* LTC_PKCS_1 */