1992-11-26 - Re: PGP on a multiuser system

Header Data

From: yanek@novavax.nova.edu (Yanek Martinson)
To: cypherpunks@toad.com
Message Hash: 6d6553e52597ce1d9a3e1d7fb81ef1e09b7688c84824322220db29426c71e8e4
Message ID: <9211261554.AA26688@novavax.nova.edu>
Reply To: <m0mudhV-0006TAC@rebma.rebma.mn.org>
UTC Datetime: 1992-11-26 15:54:44 UTC
Raw Date: Thu, 26 Nov 92 07:54:44 PST

Raw message

From: yanek@novavax.nova.edu (Yanek Martinson)
Date: Thu, 26 Nov 92 07:54:44 PST
To: cypherpunks@toad.com
Subject: Re: PGP on a multiuser system
In-Reply-To: <m0mudhV-0006TAC@rebma.rebma.mn.org>
Message-ID: <9211261554.AA26688@novavax.nova.edu>
MIME-Version: 1.0
Content-Type: text/plain


> where pgpcompose is a quick hack that looks like:
> #!/usr/bin/ksh
> 
> rm /tmp/pgpcompose
> vi /tmp/pgpcompose
> echo What key?
> read key
> pgp -mae /tmp/pgpcompose $key
> mv /tmp/pgpcompose.asc $1
> exit 0


This is not a very good way of doing this unless this is on a single-user
linux system where youhave read all the source, and compiled it yourself.

First, if on a multi-user system, what happens if two people run pgpcompose?

At the very least, use code like "vi /tmp/pgpcompose.$$", which will append
your process ID to the temp file name.

It is NOT a good idea to keep the plain text in a disk file, even for a little
while.  It would be very easy for someone to set up a crontab entry which 
looks for files of the name /tmp/pgp*, and copies them to a hidden directory.

You would never even know that it was happening.

If you absolutely MUST do crypto on a multiuser machine, at least try not to
keep plaintext or private keys in files.  

For example, you could instead rewrite the above script to call vi directly
on what will become the output cyphertext file.  Then the user types in
plaintext, and does not save the file.  The file (while still only in memory)
is piped (!G) through pgp by the user.

This is still not very secure, since it would be not too difficult for someone
to have a version of vi that saves everything that is piped in a special file.

Or pgp may be modified to do the same.  

Or if you compile pgp yourself every time, the C standard input routines
may be modified to do the logging. 

You get the picture. There is no security on a multiuser system.


--
Yanek Martinson    mthvax.cs.miami.edu!safe0!yanek     uunet!medexam!yanek
this address preferred -->> yanek@novavax.nova.edu <<-- this address preferred
Phone (305) 765-6300 daytime   FAX: (305) 765-6708  1321 N 65 Way/Hollywood
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