Des.hpp

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#pragma once
 
#include <algorithm>
#include <array>
#include <cstdint>
#include <string>

namespace lacte::vnc::des {
namespace detail {
 
inline constexpr int K_IP[64] = {
    58, 50, 42, 34, 26, 18, 10, 2, 60, 52, 44, 36, 28, 20, 12, 4,
    62, 54, 46, 38, 30, 22, 14, 6, 64, 56, 48, 40, 32, 24, 16, 8,
    57, 49, 41, 33, 25, 17, 9,  1, 59, 51, 43, 35, 27, 19, 11, 3,
    61, 53, 45, 37, 29, 21, 13, 5, 63, 55, 47, 39, 31, 23, 15, 7};
 
inline constexpr int K_FP[64] = {
    40, 8, 48, 16, 56, 24, 64, 32, 39, 7, 47, 15, 55, 23, 63, 31,
    38, 6, 46, 14, 54, 22, 62, 30, 37, 5, 45, 13, 53, 21, 61, 29,
    36, 4, 44, 12, 52, 20, 60, 28, 35, 3, 43, 11, 51, 19, 59, 27,
    34, 2, 42, 10, 50, 18, 58, 26, 33, 1, 41, 9,  49, 17, 57, 25};
 
inline constexpr int K_E[48] = {32, 1,  2,  3,  4,  5,  4,  5,  6,  7,  8,  9,
                                8,  9,  10, 11, 12, 13, 12, 13, 14, 15, 16, 17,
                                16, 17, 18, 19, 20, 21, 20, 21, 22, 23, 24, 25,
                                24, 25, 26, 27, 28, 29, 28, 29, 30, 31, 32, 1};
 
inline constexpr int K_P[32] = {16, 7, 20, 21, 29, 12, 28, 17, 1,  15, 23,
                                26, 5, 18, 31, 10, 2,  8,  24, 14, 32, 27,
                                3,  9, 19, 13, 30, 6,  22, 11, 4,  25};
 
inline constexpr int K_PC1[56] = {
    57, 49, 41, 33, 25, 17, 9,  1,  58, 50, 42, 34, 26, 18, 10, 2,  59, 51, 43,
    35, 27, 19, 11, 3,  60, 52, 44, 36, 63, 55, 47, 39, 31, 23, 15, 7,  62, 54,
    46, 38, 30, 22, 14, 6,  61, 53, 45, 37, 29, 21, 13, 5,  28, 20, 12, 4};
 
inline constexpr int K_PC2[48] = {
    14, 17, 11, 24, 1,  5,  3,  28, 15, 6,  21, 10, 23, 19, 12, 4,
    26, 8,  16, 7,  27, 20, 13, 2,  41, 52, 31, 37, 47, 55, 30, 40,
    51, 45, 33, 48, 44, 49, 39, 56, 34, 53, 46, 42, 50, 36, 29, 32};
 
inline constexpr int K_SHIFTS[16] = {1, 1, 2, 2, 2, 2, 2, 2,
                                     1, 2, 2, 2, 2, 2, 2, 1};
 
inline constexpr int K_SBOX[8][4][16] = {
    {{14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7},
     {0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8},
     {4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0},
     {15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13}},
    {{15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10},
     {3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5},
     {0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15},
     {13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9}},
    {{10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8},
     {13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1},
     {13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7},
     {1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12}},
    {{7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15},
     {13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9},
     {10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4},
     {3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14}},
    {{2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9},
     {14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6},
     {4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14},
     {11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3}},
    {{12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11},
     {10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8},
     {9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6},
     {4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13}},
    {{4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1},
     {13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6},
     {1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2},
     {6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12}},
    {{13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7},
     {1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2},
     {7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8},
     {2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11}}};

inline auto permute(const std::uint64_t src, const int src_bits,
                    const int* table, const int table_len) -> std::uint64_t {
  std::uint64_t out = 0;
  for (int i = 0; i < table_len; ++i) {
    const int shift = src_bits - table[i];
    out = (out << 1) | ((src >> shift) & 1ULL);
  }
  return out;
}
 
inline auto rotate_left_28(const std::uint32_t value, const int amount)
    -> std::uint32_t {
  constexpr std::uint32_t k_mask = (1u << 28) - 1;
  const std::uint32_t v = value & k_mask;
  return ((v << amount) | (v >> (28 - amount))) & k_mask;
}

inline auto compute_round_keys(const std::uint64_t key64,
                               std::array<std::uint64_t, 16>& round_keys)
    -> void {
  const std::uint64_t permuted = permute(key64, 64, K_PC1, 56);
  auto c = static_cast<std::uint32_t>(permuted >> 28);
  auto d = static_cast<std::uint32_t>(permuted & ((1u << 28) - 1));
  for (int round = 0; round < 16; ++round) {
    c = rotate_left_28(c, K_SHIFTS[round]);
    d = rotate_left_28(d, K_SHIFTS[round]);
    const std::uint64_t cd = (static_cast<std::uint64_t>(c) << 28) | d;
    round_keys[static_cast<std::size_t>(round)] = permute(cd, 56, K_PC2, 48);
  }
}

inline auto feistel(const std::uint32_t r, const std::uint64_t round_key48)
    -> std::uint32_t {
  const std::uint64_t expanded = permute(r, 32, K_E, 48);
  const std::uint64_t x = expanded ^ round_key48;
  std::uint32_t sbox_out = 0;
  for (int box = 0; box < 8; ++box) {
    const int shift = 48 - (box * 6 + 6);
    const auto six = static_cast<std::uint32_t>((x >> shift) & 0x3FULL);
    const std::uint32_t row = ((six & 0x20U) >> 4U) | (six & 0x01U);
    const std::uint32_t col = (six >> 1U) & 0x0FU;
    const std::uint32_t value =
        static_cast<std::uint32_t>(K_SBOX[box][row][col]);
    sbox_out = (sbox_out << 4U) | value;
  }
  return static_cast<std::uint32_t>(permute(sbox_out, 32, K_P, 32));
}
 
}  // namespace detail

[[nodiscard]] inline auto encrypt_block(const std::uint64_t plaintext,
                                        const std::uint64_t key64)
    -> std::uint64_t {
  std::array<std::uint64_t, 16> round_keys{};
  detail::compute_round_keys(key64, round_keys);
 
  const std::uint64_t ip = detail::permute(plaintext, 64, detail::K_IP, 64);
  auto l = static_cast<std::uint32_t>(ip >> 32);
  auto r = static_cast<std::uint32_t>(ip & 0xFFFFFFFFULL);
  for (int round = 0; round < 16; ++round) {
    const std::uint32_t new_r =
        l ^ detail::feistel(r, round_keys[static_cast<std::size_t>(round)]);
    l = r;
    r = new_r;
  }
  // Pre-output is R16 || L16 (the swap that alternates every round is NOT
  // re-applied after the last one) - see this file's own doc comment.
  const std::uint64_t preoutput = (static_cast<std::uint64_t>(r) << 32) | l;
  return detail::permute(preoutput, 64, detail::K_FP, 64);
}
 
inline auto bytes_to_u64(const std::array<std::uint8_t, 8>& bytes)
    -> std::uint64_t {
  std::uint64_t value = 0;
  for (const auto b : bytes) {
    value = (value << 8) | b;
  }
  return value;
}
 
inline auto u64_to_bytes(const std::uint64_t value)
    -> std::array<std::uint8_t, 8> {
  std::array<std::uint8_t, 8> out{};
  std::uint64_t remaining = value;
  for (int i = 7; i >= 0; --i) {
    out[static_cast<std::size_t>(i)] = static_cast<std::uint8_t>(remaining);
    remaining >>= 8;
  }
  return out;
}
 
namespace detail {
inline auto reverse_bits(std::uint8_t b) -> std::uint8_t {
  b = static_cast<std::uint8_t>(((b & 0xF0U) >> 4U) | ((b & 0x0FU) << 4U));
  b = static_cast<std::uint8_t>(((b & 0xCCU) >> 2U) | ((b & 0x33U) << 2U));
  b = static_cast<std::uint8_t>(((b & 0xAAU) >> 1U) | ((b & 0x55U) << 1U));
  return b;
}
}  // namespace detail

[[nodiscard]] inline auto vnc_encrypt_challenge(
    const std::array<std::uint8_t, 16>& challenge, const std::string& password)
    -> std::array<std::uint8_t, 16> {
  std::array<std::uint8_t, 8> key_bytes{};
  for (std::size_t i = 0; i < key_bytes.size(); ++i) {
    key_bytes[i] =
        i < password.size() ? static_cast<std::uint8_t>(password[i]) : 0;
  }
  for (auto& b : key_bytes) {
    b = detail::reverse_bits(b);
  }
  const std::uint64_t key64 = bytes_to_u64(key_bytes);
 
  std::array<std::uint8_t, 16> out{};
  for (int half = 0; half < 2; ++half) {
    std::array<std::uint8_t, 8> block{};
    std::copy(challenge.begin() + half * 8, challenge.begin() + half * 8 + 8,
              block.begin());
    const std::uint64_t ciphertext = encrypt_block(bytes_to_u64(block), key64);
    const auto ciphertext_bytes = u64_to_bytes(ciphertext);
    std::copy(ciphertext_bytes.begin(), ciphertext_bytes.end(),
              out.begin() + half * 8);
  }
  return out;
}
}  // namespace lacte::vnc::des