VFONT.cpp

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#include <vcryptpp/VFONT.h>
 
#include <string_view>
 
#include <BufferStream.h>
 
using namespace vcryptpp;
 
std::vector<std::byte> VFONT::decrypt(std::span<const std::byte> data) {
    BufferStreamReadOnly reader{data.data(), data.size()};
 
    if (reader.seek(SIGNATURE.length(), std::ios::end).read_string(SIGNATURE.length()) != SIGNATURE) {
        return {};
    }
    reader.seek(SIGNATURE.length() + sizeof(uint8_t), std::ios::end);
 
    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) {
        auto byte = reader.read<uint8_t>();
        outByte = static_cast<std::byte>(byte ^ magic);
        magic = byte + MAGIC;
    }
 
    return out;
}