aes.cpp

#pragma once

#include <cstdint>
#include <vector>

inline constexpr const static uint8_t sbox_forward[] = {
  0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
  0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
  0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
  0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75,
  0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84,
  0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
  0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8,
  0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2,
  0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
  0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb,
  0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79,
  0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
  0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a,
  0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e,
  0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
  0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16,
};

inline constexpr const static uint8_t sbox_reverse[] = {
  0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb,
  0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb,
  0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
  0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25,
  0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92,
  0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84,
  0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06,
  0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b,
  0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73,
  0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e,
  0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b,
  0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4,
  0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f,
  0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef,
  0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61,
  0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d,
};

template <size_t rounds = 10>
struct aes {
  static constexpr const size_t blocksize = 16;
  aes(const uint8_t* key, size_t bytes) {
    roundkeys.resize((rounds+1)*blocksize);
    uint8_t rc = 0x01;
    for (size_t n = 0; n < (rounds+1) * blocksize; n++) {
      if (n < bytes) {
        roundkeys[n] = key[n];
      } else if ((n % bytes) == 0) {
        roundkeys[n] = sbox_forward[roundkeys[n-3]] ^ roundkeys[n-bytes] ^ rc;
        rc = gf_timestwo(rc);
      } else if ((n % bytes) < 3) {
        roundkeys[n] = sbox_forward[roundkeys[n-3]] ^ roundkeys[n-bytes];
      } else if ((n % bytes) < 4) {
        roundkeys[n] = sbox_forward[roundkeys[n-7]] ^ roundkeys[n-bytes];
      } else if ((n % bytes) >= 16 && (n % bytes) < 20) {
        roundkeys[n] = roundkeys[n-bytes] ^ sbox_forward[roundkeys[n-4]];
      } else {
        roundkeys[n] = roundkeys[n-bytes] ^ roundkeys[n-4];
      }
    }
  }
  uint8_t gf_timestwo(uint8_t val) {
    if (val & 0x80) {
      return ((val & 0x7F) << 1) ^ 0x1B;
    } else {
      return val << 1;
    }
  }
  uint8_t gfmul(uint8_t a, uint8_t b) {
    uint16_t accum = 0;
    for (size_t off = 0; off < 8; off++) {
      if (b & (1 << off))
        accum ^= (a << off);
    }
    for (size_t off = 7; off --> 0;) {
      if (accum & (0x100 << off)) {
        accum ^= 0x11B << off;
      }
    }
    return (uint8_t)accum;
  }
  std::vector<uint8_t> roundkeys;
  void SubBytes(uint8_t* data) {
    for (size_t n = 0; n < blocksize; n++) {
      data[n] = sbox_forward[data[n]];
    }
  }
  void InvSubBytes(uint8_t* data) {
    for (size_t n = 0; n < blocksize; n++) {
      data[n] = sbox_reverse[data[n]];
    }
  }
  void InvMixColumns(uint8_t* data) {
    uint8_t a[blocksize];
    for (size_t n = 0; n < blocksize; n++) {
      a[n] = data[n];
    }
    for (size_t n = 0; n < blocksize; n+=4) {
      for (size_t k = 0; k < 4; k++) {
        data[n+k] = gfmul(a[n+k], 14) ^ gfmul(a[n+((k+3) % 4)], 9) ^ gfmul(a[n+((k+2)%4)], 13) ^ gfmul(a[n+((k+1)%4)], 11);
      }
    }
  }
  void MixColumns(uint8_t* data) {
    uint8_t a[blocksize];
    for (size_t n = 0; n < blocksize; n++) {
      a[n] = data[n];
    }
    for (size_t n = 0; n < blocksize; n+=4) {
      for (size_t k = 0; k < 4; k++) {
        data[n+k] = gfmul(a[n+k], 2) ^ gfmul(a[n+((k+3) % 4)], 1) ^ gfmul(a[n+((k+2)%4)], 1) ^ gfmul(a[n+((k+1)%4)], 3);
      }
    }
  }
  void InvShiftRows(uint8_t* data) {
    uint8_t tmp = data[13];
    data[13] = data[9];
    data[9] = data[5];
    data[5] = data[1];
    data[1] = tmp;

    std::swap(data[2], data[10]);
    std::swap(data[6], data[14]);

    tmp = data[3];
    data[3] = data[7];
    data[7] = data[11];
    data[11] = data[15];
    data[15] = tmp;
  }
  void ShiftRows(uint8_t* data) {
    uint8_t tmp = data[1];
    data[1] = data[5];
    data[5] = data[9];
    data[9] = data[13];
    data[13] = tmp;

    std::swap(data[2], data[10]);
    std::swap(data[6], data[14]);

    tmp = data[15];
    data[15] = data[11];
    data[11] = data[7];
    data[7] = data[3];
    data[3] = tmp;
  }
  void AddRoundKey(uint8_t* data, size_t round) {
    for (size_t n = 0; n < blocksize; n++) {
      data[n] ^= roundkeys[round * blocksize + n];
    }
  }
  void Encrypt(uint8_t* block) {
    AddRoundKey(block, 0);
    for (size_t n = 1; n < rounds; n++) {
      SubBytes(block);
      ShiftRows(block);
      MixColumns(block);
      AddRoundKey(block, n);
    }
    SubBytes(block);
    ShiftRows(block);
    AddRoundKey(block, rounds);
  }
  void Decrypt(uint8_t* block) {
    AddRoundKey(block, rounds);
    InvShiftRows(block);
    InvSubBytes(block);
    for (size_t n = rounds; --n > 0;) {
      AddRoundKey(block, n);
      InvMixColumns(block);
      InvShiftRows(block);
      InvSubBytes(block);
    }
    AddRoundKey(block, 0);
  }
};