7z2john.pl: unsupported coders/filters
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- C
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Description
In the 2026 Crack Me If You Can contest challenge 2 contained 5 .7z files that have newer coders/filters that are not supported by 7z2john.pl.
The challenge can be downloaded from https://contest-2026.korelogic.com/downloads/ and decrypted with:
gpg --batch --passphrase '46d;;Ho@]3LgfH3t-z#)' -d cmiyc_2026_challenge_2.tar.pgp > cmiyc_2026_challenge_2.tar
This produces 5 .7z files. Running 7z2john.pl gives:
$ run/7z2john.pl test_*.7z
WARNING: unsupported coder with codec id '0x040109' in file 'test_1.7z' found.
WARNING: unsupported coder with codec id '0x020304' in file 'test_2.7z' found.
WARNING: unsupported coder with codec id '0x0b' in file 'test_3.7z' found.
WARNING: unsupported coder with codec id '0x0a' in file 'test_4.7z' found.
WARNING: unsupported coder with codec id '0x020302' in file 'test_5.7z' found.
The codec IDs appear to correspond to:
| Codec ID | Method/filter |
|---|---|
| 0x040109 | Deflate64 |
| 0x020304 | Swap4 |
| 0x0b | RISC-V BCJ filter |
| 0x0a | ARM64 BCJ filter |
| 0x020302 | Swap2 |
It would be useful if 7z2john.pl could support these methods/filters when extracting hashes from encrypted 7z archives.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with run/7z2john.pl and reproduce the warnings using the five .7z files from the Crack Me If You Can challenge 2 archive. Trace how the script handles coder and filter IDs, then verify extraction against all five files. Done means the listed Deflate64, Swap4, RISC-V BCJ, ARM64 BCJ, and Swap2 methods no longer produce unsupported-coder warnings while hashes are extracted.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- perl
- Domain
- security, tooling
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 55/100