VFONT.cpp

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#include <vcryptpp/VFONT.h>
 
#include <limits>
#include <random>
#include <string_view>
 
#include <BufferStream.h>
 
using namespace vcryptpp;
 
std::vector<std::byte> VFONT::encrypt(std::span<const std::byte> data, uint8_t saltLength) {
    std::vector<std::byte> out;
    BufferStream stream{out};
 
    static std::random_device random_device{};
    static std::mt19937 generator{random_device()};
    std::uniform_int_distribution<> distribution{0, (std::numeric_limits<uint8_t>::max())};
 
    std::vector<std::byte> salt;
    salt.resize(saltLength);
 
    uint8_t magic = MAGIC;
    for (int i = 0; i < saltLength; i++) {
        salt[i] = static_cast<std::byte>(distribution(generator));
        magic ^= static_cast<uint8_t>(salt[i]) + MAGIC;
    }
 
    for (auto byte : data) {
        const uint8_t encrypted = static_cast<uint8_t>(byte) ^ magic;
        stream << encrypted;
        magic = encrypted + MAGIC;
    }
    stream
        .write(salt)
        .write<uint8_t>(saltLength + 1)
        .write(SIGNATURE, false);
 
    out.resize(stream.size());
    return out;
}
 
std::vector<std::byte> VFONT::decrypt(std::span<const std::byte> data) {
    BufferStreamReadOnly reader{data};
 
    if (reader.seek(SIGNATURE.length(), std::ios::end).read_string(SIGNATURE.length()) != SIGNATURE) {
        return {};
    }
    reader.seek(SIGNATURE.length() + sizeof(uint8_t), std::ios::end);
 
    const auto bytes = reader.read<uint8_t>();
 
    std::vector<std::byte> out;
    out.resize(reader.size() - SIGNATURE.length() - bytes);
 
    reader.seek(-static_cast<int>(bytes), std::ios::cur);
    uint8_t magic = MAGIC;
    for (int i = 0; i < bytes - 1; i++) {
        magic ^= reader.read<uint8_t>() + MAGIC;
    }
 
    reader.seek(0);
    for (auto& outByte : out) {
        const auto byte = reader.read<uint8_t>();
        outByte = static_cast<std::byte>(byte ^ magic);
        magic = byte + MAGIC;
    }
 
    return out;
}