agree

Obligatory link to MC++ song "Alice and Bob" from the 2005 album Algorhythms:

https://youtu.be/NHrugBhQfvA?si=fSwl_dupZe5VPzhf&t=407

Here's an video of RMS talking about the period referenced in that man page regarding the introduction of passwords on user accounts:

https://youtu.be/k0RYQVkQmWU?t=235

For me it brings memory of DOS applications TheDraw and ACiD Draw from the 90's BBS era. Magical times.

You'r right, the rot13 command is a shell wrapper around: ` exec /usr/bin/caesar 13 "$@" ` Forcing the key to be 13. You can obviously invoke /usr/bin/caesar with any of the 25 keys.

The use of rot13 was just an amusement in this case given its vintage. Replacing rot13 with any other simple stdin/stdout transcoder should be simple to do via the socat invocation, eg base64, a sed replace command, gzip/gunzip, even an actual symmetric encryption protocol like AES, etc.

So if you contol both ends any kind of obfuscation will defeat deep packet inspection, as long as the same obfuscation is not widely used so that the inspection software can check for it.

But if you do not control both ends, let's say you want many customers or even the public to connect to your server that's not an option.

> as long as the same obfuscation is not widely used so that the inspection software can check for it.

I imagine there are only so many things you can detect with DPI before the network connection becomes (even more) prohibitively slow. And you can check for rot13 or base64 or common compression algorithms (but beware of zip bombs), but you can't check for properly encrypted data since it will appear as random bits.