Re: Using PGP on Insecure Machines

[cactus@bb.com (L. Todd Masco)]

In article <m0qdImM-0004EcC@khijol.uucp>,
Ed Carp [Sysadmin] <khijol!erc@apple.com> wrote:
>At the risk of repeating myself, what's the problem with wrapping PGP in 
>a shell script?  Works for me - see a previous mailing, complete with 
>wrapper scripts.  I can send either encrypted or just signed email 
>without especially noticing it.

Okay, I'm the Evil NSA Sysadmin from hell.  I want to collect all the
 info available on my users.  The NSA gives me $50 per keypair, snitch
 money.  Or I just like to be able to read all your mail, and would like
 to have the option of, at some point, forging something from you.

So, I replace the shells on machines under my control with programs that
 invoke something like tee(1) to split stdin and stdout to files and then
 execs the intended shell.  For good measure, I overwrite the process
 entry in the running kernel.

So I now have a files of every keystroke you type, and if I'm clever about
 how I do it (I will be), I can correlate them with the stdout.  I just
 search for "pgp" and bingo: I've got your passphrase.

Since I'm root, getting your keyfiles is trivial.  

Your keys are toast, and you don't even know it.  There are a gazillion
 other ways the ENSFH could have done this: monitoring your /dev/tty vector
 in the kernel would be far more subtle, for example.  The key thing to
 remember is that the computer isn't your tool: it's the tool of the people
 with root.

Not only that, but I don't even have to steal your keys: the plaintext will
 exist at some time, and I can trap that -- by only twinning your stdio.
 
The network security is almost as important, since there are probably many
 more malicious people outside your machine than inside.  So, if you're
 running UNIX, you'd damn well trust everyone with root, run a logging
 /bin/login, be behind a firewall, replace the crypt that passwd uses with
 some transformation, put shadow passwd files in place, make crypt log
 usage and place appropriate monitoring software to watch the logs, monitor
 the machine from another machine behind your firewall, and a host of other
 things.

Security is not easy -- Tim's point is that you can't get it by just
 running some package;  If you think you can, you're fooling yourself
 and everytime someone puts on a securer-than-thou-because I run PGP air,
 they're showing themselves to be totally clueless.

This is all very rudimentary -- come on, you've got to be paranoid where
 security is concerned.  There are many vectors of attack and you've only
 got to miss the one that someone tries to lose big.
-- 
L. Todd Masco  | "Large prime numbers imply arrest."  - Previously meaningless
cactus@bb.com  |   grammatically correct sentence.  Now...