src/pk/rsa/rsa_encrypt_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@gmail.com, http://libtomcrypt.org
 */
#include "tomcrypt.h"

/**
  @file rsa_encrypt_key.c
  RSA PKCS OAEP encryption, Tom St Denis
*/  

#ifdef MRSA

/**
    (PKCS #1 v2.0) OAEP pad then encrypt
    @param in          The plaintext
    @param inlen       The length of the plaintext (octets)
    @param out         [out] The ciphertext
    @param outlen      [in/out] The max size and resulting size of the ciphertext
    @param lparam      The system "lparam" for the encryption
    @param lparamlen   The length of lparam (octets)
    @param prng        An active PRNG
    @param prng_idx    The index of the desired prng
    @param hash_idx    The index of the desired hash
    @param key         The RSA key to encrypt to
    @return CRYPT_OK if successful
*/    
int rsa_encrypt_key(const unsigned char *in,     unsigned long inlen,
                          unsigned char *out,    unsigned long *outlen,
                    const unsigned char *lparam, unsigned long lparamlen,
                    prng_state *prng, int prng_idx, int hash_idx, rsa_key *key)
{
  unsigned long modulus_bitlen, modulus_bytelen, x;
  int           err;
  
  LTC_ARGCHK(in     != NULL);
  LTC_ARGCHK(out    != NULL);
  LTC_ARGCHK(outlen != NULL);
  LTC_ARGCHK(key    != NULL);
  
  /* valid prng and hash ? */
  if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
     return err;
  }
  if ((err = hash_is_valid(hash_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 > *outlen) {
     return CRYPT_BUFFER_OVERFLOW;
  }
      
  /* OAEP pad the key */
  x = *outlen;
  if ((err = pkcs_1_oaep_encode(in, inlen, lparam, 
                                lparamlen, modulus_bitlen, prng, prng_idx, hash_idx, 
                                out, &x)) != CRYPT_OK) {
     return err;
  }                                

  /* rsa exptmod the OAEP pad */
  return rsa_exptmod(out, x, out, outlen, PK_PUBLIC, key);
}

#endif /* MRSA */