xmss_tools.h

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/*
 * XMSS Tools
 * (C) 2016,2017 Matthias Gierlings
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 **/
 
#ifndef BOTAN_XMSS_TOOLS_H_
#define BOTAN_XMSS_TOOLS_H_
 
#include <botan/secmem.h>
#include <algorithm>
#include <bit>
#include <iterator>
#include <type_traits>
 
namespace Botan {
 
/**
 * Helper tools for low level byte operations required
 * for the XMSS implementation.
 **/
class XMSS_Tools final {
   public:
      XMSS_Tools() = delete;
      XMSS_Tools(const XMSS_Tools&) = delete;
      void operator=(const XMSS_Tools&) = delete;
 
      /**
       * Concatenates the byte representation in big-endian order of any
       * integral value to a secure_vector.
       *
       * @param target Vector to concatenate the byte representation of the
       *               integral value to.
       * @param src integral value to concatenate.
       **/
      template <typename T, typename U = typename std::enable_if<std::is_integral<T>::value, void>::type>
      static void concat(secure_vector<uint8_t>& target, const T& src);
 
      /**
       * Concatenates the last n bytes of the byte representation in big-endian
       * order of any integral value to a to a secure_vector.
       *
       * @param target Vector to concatenate the byte representation of the
       *               integral value to.
       * @param src Integral value to concatenate.
       * @param len number of bytes to concatenate. This value must be smaller
       *            or equal to the size of type T.
       **/
      template <typename T, typename U = typename std::enable_if<std::is_integral<T>::value, void>::type>
      static void concat(secure_vector<uint8_t>& target, const T& src, size_t len);
};
 
template <typename T, typename U>
void XMSS_Tools::concat(secure_vector<uint8_t>& target, const T& src) {
   const uint8_t* src_bytes = reinterpret_cast<const uint8_t*>(&src);
   if constexpr(std::endian::native == std::endian::little) {
      std::reverse_copy(src_bytes, src_bytes + sizeof(src), std::back_inserter(target));
   } else {
      std::copy(src_bytes, src_bytes + sizeof(src), std::back_inserter(target));
   }
}
 
template <typename T, typename U>
void XMSS_Tools::concat(secure_vector<uint8_t>& target, const T& src, size_t len) {
   size_t c = static_cast<size_t>(std::min(len, sizeof(src)));
   if(len > sizeof(src)) {
      target.resize(target.size() + len - sizeof(src), 0);
   }
 
   const uint8_t* src_bytes = reinterpret_cast<const uint8_t*>(&src);
   if constexpr(std::endian::native == std::endian::little) {
      std::reverse_copy(src_bytes, src_bytes + c, std::back_inserter(target));
   } else {
      std::copy(src_bytes + sizeof(src) - c, src_bytes + sizeof(src), std::back_inserter(target));
   }
}
}  // namespace Botan
 
#endif