oxen-core/src/common/base58.cpp

// Copyright (c) 2014-2019, The Monero Project
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// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers

#include "base58.h"

#include <cassert>
#include <cstring>
#include <vector>
#include <string_view>

#include "crypto/hash.h"
#include "epee/int-util.h"
#include "varint.h"

namespace tools
{
  using namespace std::literals;
  namespace base58
  {
    namespace
    {
      constexpr std::string_view alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"sv;
      constexpr size_t full_block_size = 8;
      constexpr std::array<uint8_t, full_block_size + 1> encoded_block_sizes = {0, 2, 3, 5, 6, 7, 9, 10, 11};
      constexpr size_t full_encoded_block_size = encoded_block_sizes.back();
      constexpr std::array<int8_t, full_encoded_block_size + 1> decoded_block_sizes = {0, -1, 1, 2, -1, 3, 4, 5, -1, 6, 7, 8};
      constexpr size_t addr_checksum_size = 4;

      struct reverse_alphabet_table
      {
        std::array<int8_t, 256> from_b58_lut;
        constexpr reverse_alphabet_table() noexcept : from_b58_lut{}
        {
          for (size_t i = 0; i < from_b58_lut.size(); ++i)
            from_b58_lut[i] = -1;
          for (size_t i = 0; i < alphabet.size(); i++)
            from_b58_lut[alphabet[i]] = i;
        }

        constexpr int8_t operator[](char letter) const
        {
          return from_b58_lut[static_cast<unsigned char>(letter)];
        }
      } constexpr reverse_alphabet;

      uint64_t uint_8be_to_64(const uint8_t* data, size_t size)
      {
        assert(1 <= size && size <= sizeof(uint64_t));

        uint64_t res = 0;
        memcpy(reinterpret_cast<uint8_t*>(&res) + sizeof(uint64_t) - size, data, size);
        return SWAP64BE(res);
      }

      void uint_64_to_8be(uint64_t num, size_t size, uint8_t* data)
      {
        assert(1 <= size && size <= sizeof(uint64_t));

        uint64_t num_be = SWAP64BE(num);
        memcpy(data, reinterpret_cast<uint8_t*>(&num_be) + sizeof(uint64_t) - size, size);
      }

      void encode_block(const char* block, size_t size, char* res)
      {
        assert(1 <= size && size <= full_block_size);

        uint64_t num = uint_8be_to_64(reinterpret_cast<const uint8_t*>(block), size);
        int i = static_cast<int>(encoded_block_sizes[size]) - 1;
        while (0 < num)
        {
          uint64_t remainder = num % alphabet.size();
          num /= alphabet.size();
          res[i] = alphabet[remainder];
          --i;
        }
      }

      bool decode_block(const char* block, size_t size, char* res)
      {
        assert(1 <= size && size <= full_encoded_block_size);

        int res_size = decoded_block_sizes[size];
        if (res_size <= 0)
          return false; // Invalid block size

        uint64_t res_num = 0;
        uint64_t order = 1;
        for (size_t i = size - 1; i < size; --i)
        {
          auto digit = reverse_alphabet[block[i]];
          if (digit < 0)
            return false; // Invalid symbol

          uint64_t product_hi;
          uint64_t tmp = res_num + mul128(order, digit, &product_hi);
          if (tmp < res_num || 0 != product_hi)
            return false; // Overflow

          res_num = tmp;
          order *= alphabet.size(); // Never overflows, 58^10 < 2^64
        }

        if (static_cast<size_t>(res_size) < full_block_size && (UINT64_C(1) << (8 * res_size)) <= res_num)
          return false; // Overflow

        uint_64_to_8be(res_num, res_size, reinterpret_cast<uint8_t*>(res));

        return true;
      }
    }

    std::string encode(std::string_view data)
    {
      if (data.empty())
        return std::string();

      size_t full_block_count = data.size() / full_block_size;
      size_t last_block_size = data.size() % full_block_size;
      size_t res_size = full_block_count * full_encoded_block_size + encoded_block_sizes[last_block_size];

      std::string res(res_size, alphabet[0]);
      for (size_t i = 0; i < full_block_count; ++i)
      {
        encode_block(data.data() + i * full_block_size, full_block_size, &res[i * full_encoded_block_size]);
      }

      if (0 < last_block_size)
      {
        encode_block(data.data() + full_block_count * full_block_size, last_block_size, &res[full_block_count * full_encoded_block_size]);
      }

      return res;
    }

    bool decode(std::string_view enc, std::string& data)
    {
      if (enc.empty())
      {
        data.clear();
        return true;
      }

      size_t full_block_count = enc.size() / full_encoded_block_size;
      size_t last_block_size = enc.size() % full_encoded_block_size;
      int8_t last_block_decoded_size = decoded_block_sizes[last_block_size];
      if (last_block_decoded_size < 0)
        return false; // Invalid enc length
      size_t data_size = full_block_count * full_block_size + last_block_decoded_size;

      data.resize(data_size, 0);
      for (size_t i = 0; i < full_block_count; ++i)
      {
        if (!decode_block(enc.data() + i * full_encoded_block_size, full_encoded_block_size, &data[i * full_block_size]))
          return false;
      }

      if (0 < last_block_size)
      {
        if (!decode_block(enc.data() + full_block_count * full_encoded_block_size, last_block_size,
          &data[full_block_count * full_block_size]))
          return false;
      }

      return true;
    }

    std::string encode_addr(uint64_t tag, std::string_view data)
    {
      std::string buf = get_varint_data(tag);
      buf += data;
      crypto::hash hash = crypto::cn_fast_hash(buf.data(), buf.size());
      const char* hash_data = reinterpret_cast<const char*>(&hash);
      buf.append(hash_data, addr_checksum_size);
      return encode(buf);
    }

    bool decode_addr(std::string_view addr, uint64_t& tag, std::string& data)
    {
      std::string addr_data;
      bool r = decode(addr, addr_data);
      if (!r) return false;
      if (addr_data.size() <= addr_checksum_size) return false;

      std::string checksum(addr_checksum_size, '\0');
      checksum = addr_data.substr(addr_data.size() - addr_checksum_size);

      addr_data.resize(addr_data.size() - addr_checksum_size);
      crypto::hash hash = crypto::cn_fast_hash(addr_data.data(), addr_data.size());
      std::string expected_checksum(reinterpret_cast<const char*>(&hash), addr_checksum_size);
      if (expected_checksum != checksum) return false;

      int read = tools::read_varint(addr_data.begin(), addr_data.end(), tag);
      if (read <= 0) return false;

      data = addr_data.substr(read);
      return true;
    }
  }
}