1. The file is a gzip archive:```% gunzip -vl Parcelmethod  crc     date  time    compressed uncompressed  ratio uncompressed_namedefla 1564e121 Apr 14 05:27       439516       759456  42.1% Parcel```
Ungzip: `gunzip -c Parcel > parcel_content` 2. Look at the text file inside. Notice that it has 2 types of content (apart from multiparts): text and png images:```% cat parcel_content | grep Content-Type | sort | uniqContent-Type: image/pngContent-Type: multipart/mixed; boundary="===============0000136577486898548=="...Content-Type: text/plain; charset="us-ascii"```
Let's ignore text and focuse on images. 3. Extract images:
```% cat extractor.pyimport sysimport base64
if __name__ == '__main__':    with open(sys.argv[1], 'rt') as fin:        lines = [line for line in fin]    i = 0    file_count = 0    seen_b64_contents = set()    while i < len(lines):        if 'Content-Type: image/png' in lines[i]:            assert 'MIME-Version: 1.0' in lines[i + 1]            assert 'Content-Transfer-Encoding: base64' in lines[i + 2]            assert '' == lines[i + 3].strip()            i += 4            b64_content = ''            while lines[i].strip() != '':                b64_content += lines[i]                i += 1
            if b64_content not in seen_b64_contents:                seen_b64_contents.add(b64_content)                with open('img_{}.png'.format(1 + file_count), 'wb') as fout:                    content = base64.decodebytes(b64_content.encode())                    fout.write(content)                    file_count += 1                print('Extracted image #{}'.format(file_count))        i += 1
% python3 extractor.py parcel_contentExtracted image #1...Extracted image #25``` 4. Notice some images have letters. Import them to any visual editor (I used draw.io), drop those without letters, reorder and get the flag:![](https://i.imgur.com/JL8PZe9.png) 
Flag is `RS{Im_doing_a_v1rtual_puzzl3}`.