/**
 * XMSS WOTS Parameters
 * Descibes a signature method for XMSS Winternitz One Time Signatures,
 * as defined in:
 * [1] XMSS: Extended Hash-Based Signatures,
 *     draft-itrf-cfrg-xmss-hash-based-signatures-06
 *     Release: July 2016.
 *     https://datatracker.ietf.org/doc/
 *     draft-irtf-cfrg-xmss-hash-based-signatures/?include_text=1
 *
 * (C) 2016 Matthias Gierlings
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 **/

#include <botan/xmss_wots_parameters.h>

namespace Botan {

const std::map<std::string, XMSS_WOTS_Parameters::ots_algorithm_t>
   XMSS_WOTS_Parameters::m_oid_name_lut =
   {
   { "WOTSP_SHA2-256_W16", WOTSP_SHA2_256_W16 },
   { "WOTSP_SHA2-512_W16", WOTSP_SHA2_512_W16 }
   };

XMSS_WOTS_Parameters::XMSS_WOTS_Parameters(const std::string& algo_name)
   : XMSS_WOTS_Parameters(m_oid_name_lut.at(algo_name))
   {}

XMSS_WOTS_Parameters::XMSS_WOTS_Parameters(ots_algorithm_t oid)
   : m_oid(oid)
   {
   switch(oid)
      {
      case WOTSP_SHA2_256_W16:
         m_element_size = 32;
         m_w = 16;
         m_len = 67;
         m_name = "WOTSP_SHA2-256_W16";
         m_hash_name = "SHA-256";
         m_strength = 256;
         break;
      case WOTSP_SHA2_512_W16:
         m_element_size = 64;
         m_w = 16;
         m_len = 131;
         m_name = "WOTSP_SHA2-512_W16";
         m_hash_name = "SHA-512";
         m_strength = 512;
         break;
// FIXME: Uncomment once SHAKE128/256 implementation is available in Botan.
//      case WOTSP_SHAKE128_W16:
//         m_element_size = 32;
//         m_w = 16;
//         m_len = 67;
//         m_name = "WOTSP_SHAKE128_W16";
//         m_hash_name = "<MISSING>";
//         m_strength = 256;
//         break;
//      case WOTSP_SHAKE256_W16:
//         m_element_size = 64;
//         m_w = 16;
//         m_len = 131;
//         m_name = "WOTSP_SHAKE256_W16";
//         m_hash_name = "<MISSING>";
//         m_strength = 512;
//         break;
      default:
         throw Unsupported_Argument(
            "Algorithm id does not match any XMSS WOTS algorithm id.");
         break;
      }

   m_w == 16 ? m_lg_w = 4 : m_lg_w = 2;
   m_len_1 = static_cast<size_t>(ceil((8 * element_size()) / m_lg_w));
   m_len_2 = static_cast<size_t>(
      floor(log2(m_len_1 * (wots_parameter() - 1)) / m_lg_w) + 1);
   BOTAN_ASSERT(m_len == m_len_1 + m_len_2, "Invalid XMSS WOTS parameter "
                "\"len\" detedted.");
   }

secure_vector<byte>
XMSS_WOTS_Parameters::base_w(const secure_vector<byte>& msg, size_t out_size) const
   {
   secure_vector<byte> result;
   size_t in = 0;
   size_t total = 0;
   size_t bits = 0;

   for(size_t i = 0; i < out_size; i++)
      {
      if(bits == 0)
         {
         total = msg[in];
         in++;
         bits += 8;
         }
      bits -= m_lg_w;
      result.push_back(static_cast<byte>((total >> bits) & (m_w - 1)));
      }
   return result;
   }

secure_vector<byte>
XMSS_WOTS_Parameters::base_w(size_t value) const
   {
   value <<= (8 - ((m_len_2 * m_lg_w) % 8));
   size_t len_2_bytes = static_cast<size_t>(
      ceil(static_cast<float>(m_len_2 * m_lg_w) / 8.f));
   secure_vector<byte> result;
   XMSS_Tools::concat(result, value, len_2_bytes);
   return base_w(result, m_len_2);
   }

void
XMSS_WOTS_Parameters::append_checksum(secure_vector<byte>& data)
   {
   size_t csum = 0;

   for(size_t i = 0; i < data.size(); i++)
      {
      csum += wots_parameter() - 1 - data[i];
      }

   secure_vector<byte> csum_bytes = base_w(csum);
   std::move(csum_bytes.begin(), csum_bytes.end(), std::back_inserter(data));
   }

}