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// Cybersecurity clarified.

Decode AZTEC from Vehicle Registration Docs (C++)

2022-05-23   Dawid Farbaniec
...
A two-dimensional code can be seen in the vehicle registration documents. This is the Aztec 2D code and, as you can guess, it was supposed to improve the reading of data from this document. I would not be interested in it, if it were not for the fact that the way data is encoded in it - until now - was known only to a small group of people. As I remember, the topic was taken up for the first time on wykop.pl (thanks!), Then the topic was discussed by other websites (e.g. zaufanatrzeciastrona.pl), people etc.

Read more here:
https://zaufanatrzeciastrona.pl/post/historia-o-dowodach-rejestracyjnych-dekoderze-aztec-i-pewnym-monopolu/ [access: 2022-05-23]

C++ implementation by ethical.blue

/*

* C++ implementation of NRV2E decompression algorithm
* which was used in this project to decode
* Aztec 2D from Polish Vehicle Registration Documents
* - by https://ethical.blue 2019 (last edit: October 2020)
*
* Based on original UCL library written by:
* Markus F.X.J. Oberhumer <[email protected]>
* http://www.oberhumer.com/opensource/ucl/
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU General Public License for more details.
*/

#include <fstream>
#include <vector>

const signed START_OFFSET { 4 };
signed ilen { START_OFFSET };
unsigned current_bit { 0 };
std::byte current_byte { 0 };
std::vector<std::byte> src { 0 };

static unsigned get_bit()
{
    if (ilen >= src.size())
        throw std::invalid_argument("Przesunięcie jest poza zakresem.");

    if (current_bit == 0)
    {
        current_byte = src[ilen++];
        current_bit = 8;
    }

    return (static_cast<unsigned>(current_byte) >> --current_bit) & 1;
}

static std::vector<std::byte> decompress_NRV2E(const std::vector<std::byte>& source_data)
{
    src = source_data;

    unsigned dest_size { static_cast<unsigned>(src[0]) bitor
                         static_cast<unsigned>(src[1]) << 8u bitor
                         static_cast<unsigned>(src[2]) << 16u bitor
                         static_cast<unsigned>(src[3]) << 24u };
    
    std::vector<std::byte> dst(dest_size);

    unsigned olen { 0 };
    unsigned last_m_off { 1 };

    while (ilen < src.size())
    {
        unsigned m_off { 0 };
        unsigned m_len { 0 };

        while (get_bit() == 1)
        {
            dst[olen++] = src[ilen++];
        }

        m_off = 1;
        while (true)
        {
            m_off = m_off * 2 + get_bit();
            if (get_bit() == 1)
                break;
            m_off = (m_off - 1) * 2 + get_bit();
        }

        if (m_off == 2)
        {
            m_off = last_m_off;
            m_len = get_bit();
        }
        else
        {
            m_off = (m_off - 3) * 256 + static_cast<unsigned>(src[ilen++]);
            if (m_off == std::numeric_limits<unsigned>().max())
                break;
            m_len = (m_off ^ std::numeric_limits<unsigned>().max()) & 1;
            m_off >>= 1;
            last_m_off = ++m_off;
        }
        if (m_len > 0)
            m_len = 1 + get_bit();
        else if (get_bit() == 1)
            m_len = 3 + get_bit();
        else
        {
            m_len++;
            do
            {
                m_len = m_len * 2 + get_bit();
            } while (get_bit() == 0);
            m_len += 3;
        }
        m_len += m_off > 0x500 ? 1 : 0;

        unsigned m_pos { 0 };
        m_pos = olen - m_off;

        dst[olen++] = dst[m_pos++];
        do dst[olen++] = dst[m_pos++]; while (--m_len > 0);
    }
    return dst;
}

static std::vector<std::byte> base64_decode(const std::vector<std::byte>& in) {

    std::vector<std::byte> out { 0 };

    std::vector<int> T(256, -1);
    for (int i = 0; i < 64; i++)
        T["ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"[i]] = i;

    signed val { 0 };
    signed valb { -8 };
    for (auto b : in)
    {
        if (T[static_cast<unsigned>(b)] == -1) break;
        val = (val << 6) + T[static_cast<unsigned>(b)];
        valb += 6;
        if (valb >= 0)
        {
            out.push_back(static_cast<std::byte>((val >> valb) & 0xFF));
            valb -= 8;
        }
    }
    return out;
}

int main()
{
    std::string test1 { "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" };

    if (test1.length() % 2 == 1)
        test1[test1.length() - 1] = u8'\0';

    std::vector<std::byte> text_bytes { 0 };

    for (char c : test1)
        text_bytes.push_back(static_cast<std::byte>(c));

    std::vector<std::byte> decoded = base64_decode(text_bytes);
    std::vector<std::byte> decompressed = decompress_NRV2E(decoded);
    std::u16string plain_data { 0 };
    plain_data.assign(reinterpret_cast<std::u16string::const_pointer>(&decompressed[0]), decompressed.size() / sizeof(std::u16string::value_type));

    /* Zapisz rozkodowane dane do pliku tekstowego
       (zmień ścieżkę według swojego systemu) */
    std::basic_ofstream<char16_t> outfile("C:\Users\x\Desktop\Nowy folder\file1.txt", std::ios_base::binary);
    outfile.write(plain_data.c_str(), plain_data.length());
    outfile.close();

    std::string visit { "https://ethical.blue" };

    return EXIT_SUCCESS;
}

Bibliography

https://zaufanatrzeciastrona.pl/post/historia-o-dowodach-rejestracyjnych-dekoderze-aztec-i-pewnym-monopolu/ [access: 2022-05-23]

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