🚀 go-pugleaf

In article <1bfo95INN6a4@nym.ossi.com> aegl@ossi.com (Tony Luck) writes:
>barmar@think.com (Barry Margolin) writes:
>>In article <1992Oct13.172459.28720@zip.eecs.umich.edu> ayman@eecs.umich.edu (Ayman I. Kayssi) writes:
>>>I posted a question on comp.unix.questions about how to get a shell by email,
>>>that is a shell that would execute what's in the body of an email message.
>>>All the details have been worked out except for one thing: security.
>
>>How about this:
>
>>Include in the header a string in both plaintext and encrypted form.  The
>>receiving system would decrypt the encrypted form and compare it to the
>>plaintext.
>
>>One problem with this is that it's quite amenable to known-plaintext
>>attacks.  And it also requires a decryption key to be stored on the
>>destination system, unless you use a public-key encryption system.
>
>Such a system would be easily spoofed by a "replay" attack.  If I ever get
>hold of one of the messages, I just take the header (which has a valid key
>on it) attach a different shell script, and send it!  Bang!

How about encode a sequence number, and disallow repeated sequence numbers?

The replay attack goes away.  However, a sysop on the route your message
travels could copy your message, replace the commands, and send his message
*before* your message.  Significantly harder, but it's not A1 security.