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

/**
  @file pkcs_1_oaep_encode.c
  OAEP Padding for PKCS #1, Tom St Denis
*/

#ifdef LTC_PKCS_1

/**
  PKCS #1 v2.00 OAEP encode
  @param msg             The data to encode
  @param msglen          The length of the data to encode (octets)
  @param lparam          A session or system parameter (can be NULL)
  @param lparamlen       The length of the lparam data
  @param modulus_bitlen  The bit length of the RSA modulus
  @param prng            An active PRNG state
  @param prng_idx        The index of the PRNG desired
  @param hash_idx        The index of the hash desired
  @param out             [out] The destination for the encoded data
  @param outlen          [in/out] The max size and resulting size of the encoded data
  @return CRYPT_OK if successful
*/
int pkcs_1_oaep_encode(const unsigned char *msg,    unsigned long msglen,
                       const unsigned char *lparam, unsigned long lparamlen,
                             unsigned long modulus_bitlen, prng_state *prng,
                             int           prng_idx,
                             int           mgf_hash, int lparam_hash,
                             unsigned char *out,    unsigned long *outlen)
{
   unsigned char *DB, *seed, *mask;
   unsigned long hLen, x, y, modulus_len;
   int           err, lparam_hash_used;

   LTC_ARGCHK((msglen == 0) || (msg != NULL));
   LTC_ARGCHK(out    != NULL);
   LTC_ARGCHK(outlen != NULL);

   /* test valid hash */
   if ((err = hash_is_valid(mgf_hash)) != CRYPT_OK) {
      return err;
   }
   if (lparam_hash != -1) {
      if ((err = hash_is_valid(lparam_hash)) != CRYPT_OK) {
         return err;
      }
      lparam_hash_used = lparam_hash;
   } else {
      lparam_hash_used = mgf_hash;
   }

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

   hLen        = hash_descriptor[lparam_hash_used].hashsize;
   modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);

   /* test message size */
   if ((2*hLen >= (modulus_len - 2)) || (msglen > (modulus_len - 2*hLen - 2))) {
      return CRYPT_PK_INVALID_SIZE;
   }

   /* allocate ram for DB/mask/salt of size modulus_len */
   DB   = XMALLOC(modulus_len);
   mask = XMALLOC(modulus_len);
   seed = XMALLOC(hLen);
   if (DB == NULL || mask == NULL || seed == NULL) {
      if (DB != NULL) {
         XFREE(DB);
      }
      if (mask != NULL) {
         XFREE(mask);
      }
      if (seed != NULL) {
         XFREE(seed);
      }
      return CRYPT_MEM;
   }

   /* get lhash */
   /* DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */
   x = modulus_len;
   if (lparam != NULL) {
      if ((err = hash_memory(lparam_hash_used, lparam, lparamlen, DB, &x)) != CRYPT_OK) {
         goto LBL_ERR;
      }
   } else {
      /* can't pass hash_memory a NULL so use `out` with zero length */
      if ((err = hash_memory(lparam_hash_used, out, 0, DB, &x)) != CRYPT_OK) {
         goto LBL_ERR;
      }
   }

   /* append PS then 0x01 (to lhash)  */
   x = hLen;
   y = modulus_len - msglen - 2*hLen - 2;
   XMEMSET(DB+x, 0, y);
   x += y;

   /* 0x01 byte */
   DB[x++] = 0x01;

   if (msglen != 0) {
      /* message (length = msglen) */
      XMEMCPY(DB+x, msg, msglen);
      x += msglen;
   }

   /* now choose a random seed */
   if (prng_descriptor[prng_idx].read(seed, hLen, prng) != hLen) {
      err = CRYPT_ERROR_READPRNG;
      goto LBL_ERR;
   }

   /* compute MGF1 of seed (k - hlen - 1) */
   if ((err = pkcs_1_mgf1(mgf_hash, seed, hLen, mask, modulus_len - hLen - 1)) != CRYPT_OK) {
      goto LBL_ERR;
   }

   /* xor against DB */
   for (y = 0; y < (modulus_len - hLen - 1); y++) {
       DB[y] ^= mask[y];
   }

   /* compute MGF1 of maskedDB (hLen) */
   if ((err = pkcs_1_mgf1(mgf_hash, DB, modulus_len - hLen - 1, mask, hLen)) != CRYPT_OK) {
      goto LBL_ERR;
   }

   /* XOR against seed */
   for (y = 0; y < hLen; y++) {
      seed[y] ^= mask[y];
   }

   /* create string of length modulus_len */
   if (*outlen < modulus_len) {
      *outlen = modulus_len;
      err = CRYPT_BUFFER_OVERFLOW;
      goto LBL_ERR;
   }

   /* start output which is 0x00 || maskedSeed || maskedDB */
   x = 0;
   out[x++] = 0x00;
   XMEMCPY(out+x, seed, hLen);
   x += hLen;
   XMEMCPY(out+x, DB, modulus_len - hLen - 1);
   x += modulus_len - hLen - 1;

   *outlen = x;

   err = CRYPT_OK;
LBL_ERR:
#ifdef LTC_CLEAN_STACK
   zeromem(DB,   modulus_len);
   zeromem(seed, hLen);
   zeromem(mask, modulus_len);
#endif

   XFREE(seed);
   XFREE(mask);
   XFREE(DB);

   return err;
}

#endif /* LTC_PKCS_1 */

