pcap2john: Add SNMPv3 parser

[AlbertVeli]

This adds support for extracting SNMPv3 USM hashes. The parser handles both authentication-only (authNoPriv) and authentication with privacy (authPriv) modes.

Hashes are printed in $SNMPv3$ format, with authProto set to 0 to allow John to try both MD5 and SHA1. If the authProto is known the 0 can be changed to 1 (MD5) or 2 (SHA1). This is not done automatically.

[AlbertVeli]

Since I was assisted by ChatGPT-4o when writing this I asked about licensing and it responded with the following suggestion for licensing information.

This code is my original contribution, written with assistance from
ChatGPT. I am submitting it under the terms of the GPLv2+ license as
required by the John the Ripper project.

It may still need some refactoring. Does it support all formats that snmp_fmt_plug.c supports? Can the SNMP plugin crack the (optional) encryption password too? This only extracts the authentication password hash.

[solardiz]

Thank you for your contribution @AlbertVeli! I intend to take a closer look a bit later.

[solardiz]

@AlbertVeli What input files did you test this with? I notice that comments in snmp_fmt_plug.c have URLs and filenames for pcap files corresponding to the test vectors. I think we should make copies of those files in our https://github.com/openwall/john-samples repo - can you please send us a pull request with that?

@kholia How did you create those test vectors? Is there possibly already an extraction tool that @AlbertVeli has missed?

GPLv2+ license as required by the John the Ripper project.

We actually prefer our cut-down BSD license where possible, please see doc/pcap2john.readme for licenses that apply to this script. I suggest you add a similar copyright statement + license for your contribution. If you add to that documentation file, then you'll also need to revise its initial wording that currently says it's only about "prior copyright headers" (yours wouldn't be "prior", but is a new addition).

Seeing the commit history for pcap2john.py, I think @exploide should also add a copyright statement + license.

Maybe we should collect the copyright statements and list them in the script itself (one line per person) and group them by license (most are our cut-down BSD), but I see one contribution is GPLv3 (unfortunately).