Re: don't use passwords as private keys (was Re: Using a password as a private key.)

[Adam Back <aba@dcs.ex.ac.uk>]

Harv "RedRook" (is that Harvey Rook?) writes:
> You don't know you have to destroy a key file, until it is too late.

Sooo.  What does this imply you should do?  Destroy your key file on a
regular basis :-)

eg. this key:

pub  2048/2E17753D 1998/10/04 Adam Back <aba@dcs.ex.ac.uk> (FS key, Oct 98)

will be destroyed tomorrow ("FS" = Forward Secrecy), the key is my
forward secret key for October.  And this one was destroyed at the end
of last month:

pub  2048/xxxxxxxx 1998/09/01 Adam Back <aba@dcs.ex.ac.uk> (FS key, Nov 98)

etc.

This means that if someone were (say like GCHQ or ECHELON) were to be
archiving my email, and later develop an interest in reading it, they
would be out of luck.  And I wouldn't be able to help them if I wanted
to.

> Until then, it's just laying around waiting for some one to copy and
> crack. If you are paranoid enough to assume your opponent is going to
> torcher you to get your signature password, you should assume that he
> already has your keyfile, and is willing to torcher you to get it's
> password.

Forward secrecy means that only the current key file is vulnerable.

> Thus coercion and dicitonary attacks are moot points. That is, if your
> password is good enough.

Your passphrase might not be as secure as you think it is.  The sound
of you typing it whilst on the phone, or the RF noise emitted by the
keyboard controller chip may completely or partially leak it.

Adam