rsa_encrypt_key.c

/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
#include "tomcrypt_private.h"

/**
  @file rsa_encrypt_key.c
  RSA PKCS #1 encryption, Tom St Denis and Andreas Lange
*/

#ifdef LTC_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 padding     Type of padding (LTC_PKCS_1_OAEP or LTC_PKCS_1_V1_5)
    @param key         The RSA key to encrypt to
    @return CRYPT_OK if successful
*/
int rsa_encrypt_key_ex(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, int            padding,
                       const rsa_key       *key)
{
  unsigned long modulus_bitlen, modulus_bytelen, x;
  int           err;

  LTC_ARGCHK((inlen == 0) || (in != NULL));
  LTC_ARGCHK(out    != NULL);
  LTC_ARGCHK(outlen != NULL);
  LTC_ARGCHK(key    != NULL);

  /* valid padding? */
  if ((padding != LTC_PKCS_1_V1_5) &&
      (padding != LTC_PKCS_1_OAEP)) {
    return CRYPT_PK_INVALID_PADDING;
  }

  /* valid prng? */
  if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
     return err;
  }

  if (padding == LTC_PKCS_1_OAEP) {
    /* valid hash? */
    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) {
     *outlen = modulus_bytelen;
     return CRYPT_BUFFER_OVERFLOW;
  }

  if (padding == LTC_PKCS_1_OAEP) {
    /* 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;
    }
  } else {
    /* PKCS #1 v1.5 pad the key */
    x = *outlen;
    if ((err = pkcs_1_v1_5_encode(in, inlen, LTC_PKCS_1_EME,
                                  modulus_bitlen, prng, prng_idx,
                                  out, &x)) != CRYPT_OK) {
      return err;
    }
  }

  /* rsa exptmod the OAEP or PKCS #1 v1.5 pad */
  return ltc_mp.rsa_me(out, x, out, outlen, PK_PUBLIC, key);
}

#endif /* LTC_MRSA */