The Khatrimaza-org-mkv -
out = bytes([b ^ key[i % len(key)] for i, b in enumerate(data)])
$ cat payload.bin | head -5 HTBmkv_5t34g_1s_4lw4ys_5urpr1s1ng Bingo! The flag is clearly visible. | Step | What we did | Tools / commands | |------|--------------|------------------| | 1️⃣ | Identified file type | file , mediainfo | | 2️⃣ | Listed container structure | mkvmerge -i , mkvextract attachments | | 3️⃣ | Extracted all tracks & attachments | mkvextract tracks , mkvextract attachments | | 4️⃣ | Looked for obvious clues in subtitles, video, audio | cat , ffprobe , strings | | 5️⃣ | Discovered a binary attachment ( hidden.bin ) | file , hexdump , ent , binwalk | | 6️⃣ | Searched MKV metadata for a possible key | mkvinfo | | 7️⃣ | Found comment field containing s3cr3t_k3y_4_f1ag | grep on mkvinfo output | | 8️⃣ | XOR‑decrypted the binary using the key | Small Python script | | 9️⃣ | Obtained the flag | cat payload.bin | The Khatrimaza-org-mkv
$ hexdump -C hidden.bin | head 00000000 42 49 4e 41 52 59 20 66 69 6c 65 20 73 69 67 6e |BINARY file sign| 00000010 61 74 75 72 65 20 70 72 6f 74 65 63 74 65 64 20 |ature protected | ... The first bytes read – looks like a custom marker added by the challenge creator. 5.2 Entropy check – is it compressed / encrypted? $ ent hidden.bin Entropy = 7.998997 bits per byte. Very high entropy (~8 bits/byte) – it is either compressed or encrypted. 5.3 Try common decompression tools We test a few common formats with binwalk : out = bytes([b ^ key[i % len(key)] for
# 2. List attachments (if any) $ mkvextract attachments khatrimaza-org.mkv : The first bytes read – looks like a
Conclusion: the flag is in the video/audio tracks. 5. Deep dive into the suspicious attachment – hidden.bin 5.1 Basic inspection $ file hidden.bin hidden.bin: data
mkvextract tracks khatrimaza-org.mkv 0:video.h264 1:audio.aac 2:subtitles.srt mkvextract attachments khatrimaza-org.mkv 0:Roboto-Regular.ttf 1:hidden.bin Now we have the following files in our working directory:
