1  // Copyright (c) 2025-present The Bitcoin Core developers
  2  // Distributed under the MIT software license, see the accompanying
  3  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  4  
  5  #ifndef BITCOIN_UTIL_OBFUSCATION_H
  6  #define BITCOIN_UTIL_OBFUSCATION_H
  7  
  8  #include <crypto/hex_base.h>
  9  #include <span.h>
 10  #include <tinyformat.h>
 11  #include <util/strencodings.h>
 12  
 13  #include <array>
 14  #include <bit>
 15  #include <climits>
 16  #include <cstdint>
 17  #include <ios>
 18  #include <memory>
 19  
 20  class Obfuscation
 21  {
 22  public:
 23      using KeyType = uint64_t;
 24      static constexpr size_t KEY_SIZE{sizeof(KeyType)};
 25  
 26      Obfuscation() { SetRotations(0); }
 27      explicit Obfuscation(std::span<const std::byte, KEY_SIZE> key_bytes)
 28      {
 29          SetRotations(ToKey(key_bytes));
 30      }
 31  
 32      operator bool() const { return m_rotations[0] != 0; }
 33  
 34      void operator()(std::span<std::byte> target, size_t key_offset = 0) const
 35      {
 36          if (!*this) return;
 37  
 38          KeyType rot_key{m_rotations[key_offset % KEY_SIZE]}; // Continue obfuscation from where we left off
 39          if (target.size() > KEY_SIZE) {
 40              // Obfuscate until KEY_SIZE alignment boundary
 41              if (const auto misalign{reinterpret_cast<uintptr_t>(target.data()) % KEY_SIZE}) {
 42                  const size_t alignment{KEY_SIZE - misalign};
 43                  XorWord(target.first(alignment), rot_key);
 44  
 45                  target = {std::assume_aligned<KEY_SIZE>(target.data() + alignment), target.size() - alignment};
 46                  rot_key = m_rotations[(key_offset + alignment) % KEY_SIZE];
 47              }
 48              // Aligned obfuscation in 8*KEY_SIZE chunks
 49              for (constexpr auto unroll{8}; target.size() >= KEY_SIZE * unroll; target = target.subspan(KEY_SIZE * unroll)) {
 50                  for (size_t i{0}; i < unroll; ++i) {
 51                      XorWord(target.subspan(i * KEY_SIZE, KEY_SIZE), rot_key);
 52                  }
 53              }
 54              // Aligned obfuscation in KEY_SIZE chunks
 55              for (; target.size() >= KEY_SIZE; target = target.subspan(KEY_SIZE)) {
 56                  XorWord(target.first<KEY_SIZE>(), rot_key);
 57              }
 58          }
 59          XorWord(target, rot_key);
 60      }
 61  
 62      template <typename Stream>
 63      void Serialize(Stream& s) const
 64      {
 65          // Use vector serialization for convenient compact size prefix.
 66          std::vector<std::byte> bytes{KEY_SIZE};
 67          std::memcpy(bytes.data(), &m_rotations[0], KEY_SIZE);
 68          s << bytes;
 69      }
 70  
 71      template <typename Stream>
 72      void Unserialize(Stream& s)
 73      {
 74          std::vector<std::byte> bytes{KEY_SIZE};
 75          s >> bytes;
 76          if (bytes.size() != KEY_SIZE) throw std::ios_base::failure(strprintf("Obfuscation key size should be exactly %s bytes long", KEY_SIZE));
 77          SetRotations(ToKey(std::span<std::byte, KEY_SIZE>(bytes)));
 78      }
 79  
 80      std::string HexKey() const
 81      {
 82          return HexStr(std::as_bytes(std::span{&m_rotations[0], 1}));
 83      }
 84  
 85  private:
 86      // Cached key rotations for different offsets.
 87      std::array<KeyType, KEY_SIZE> m_rotations;
 88  
 89      void SetRotations(KeyType key)
 90      {
 91          for (size_t i{0}; i < KEY_SIZE; ++i) {
 92              int key_rotation_bits{int(CHAR_BIT * i)};
 93              if constexpr (std::endian::native == std::endian::big) key_rotation_bits *= -1;
 94              m_rotations[i] = std::rotr(key, key_rotation_bits);
 95          }
 96      }
 97  
 98      static KeyType ToKey(std::span<const std::byte, KEY_SIZE> key_span)
 99      {
100          KeyType key{};
101          std::memcpy(&key, key_span.data(), KEY_SIZE);
102          return key;
103      }
104  
105      static void XorWord(std::span<std::byte> target, KeyType key)
106      {
107          assert(target.size() <= KEY_SIZE);
108          if (target.empty()) return;
109          KeyType raw{};
110          std::memcpy(&raw, target.data(), target.size());
111          raw ^= key;
112          std::memcpy(target.data(), &raw, target.size());
113      }
114  };
115  
116  #endif // BITCOIN_UTIL_OBFUSCATION_H