public accounts / PGP / passphrases

[Mike Duvos]

lmccarth at ducie.cs.umass.edu writes:

 > Could someone please elaborate on the foolishness of using
 > PGP with a passphrase on a public machine (as I do) ?

It is not secure to use your private key on a machine that you do
not have physical control over.  It is probably secure to store a
passphrase-protected private key on such a machine, as long as
you do not feed it into a program which decrypts it.

 > Am I wrong in thinking that my secret key is useless to an
 > intruder until she guesses my passphrase ?

Or monitors your keystrokes as you type in your passphrase, or
watches your address space as PGP uses the key, etc etc...

Given the state of Unix security, I would certainly not want to
type my passphrase into a Unix box unless I was the only user,
was directly connected to the box through a wire I could see, and
had just done a fresh boot after verifying the MD5 hash on all
the OS binaries.

Not likely to be the case at your average public installation.

 > I have no net access except via an account on a public
 > machine, so I'm not about to start storing my secret key
 > elsewhere, but I'll change my passphrase to <null> if it's
 > irrelevant anyway.

Having a passphrase will protect against casual acquisition of
your private key, but only physical security when the key is used
will protect you against a determined opponent.

---

As long as I am typing, permit me to add my two cents to the
"digital signatures on the list" flame war.

Like many proponents of strong cryptography, I rarely use it in
everyday life.  I occasionally encrypt personal mail to friends
overseas when I know it is going to take numerous hops over
insecure links en route, and I will digitally sign mail or Usenet
articles if I want to say something that I consider important in
a way that cannot be altered or spoofed.  This happens rarely.

I would consider having to digitally sign everything I post to
the list, no matter how frivilous, the moral equivalent of being
allowed to speak only while under sworn oath.  Now oaths and
notaries are certainly useful things in appropriate places, like
courtrooms and lawyers offices, but I don't think any of us would
care to live our lives having our every utterance subject to
their certification.

It would certainly not aid our cause to have the government be
able to point and say - "Even the cypherpunks make people
digitally identify themselves when posting messages to their
list" - while at the same time attempting to explain to people
why we aren't happy with Chaum's less than anonymous ECash or Web
sites that require registration and personal information before
permitting access to privacy-related material.

The Net, like life, offers a certain plausable deniability in
what has been said, and who has said it.  Some of the best
messages on the list in past years have been Tim's witty and
entertaining spoofs of his ideological opponents.  Let's save
absolute certainty about the real or pseudo-anonymous identities
of speakers in this forum for times when, in the sole opinion of
the person posting, such certainty is deemed necessary.

-- 
     Mike Duvos         $    PGP 2.6 Public Key available     $
     mpd at netcom.com     $    via Finger.                      $