feature request: allowing display of session key used for encryption

David Shaw dshaw at jabberwocky.com
Sat Dec 13 09:35:03 CET 2003

On Sat, Dec 13, 2003 at 02:32:01AM +0100, Peter Palfrader wrote:
> On Wed, 10 Dec 2003, David Shaw wrote:
> > On Thu, Dec 11, 2003 at 12:29:14AM +0100, Ingo Klöcker wrote:
> > > On Wednesday 10 December 2003 23:45, vedaal at hush.com wrote:
> > > > On Wed, 10 Dec 2003 14:30:46 -0800 Steve Butler <sbutler at fchn.com> 
> > > wrote:
> > > > >Why not always encrypt to yourself as one of the recipients?
> > > >
> > > > for those times when the sender wants more e-mail anonymity
> > > 
> > > --throw-keyid ? Sure it throws away the key id of all encryption keys. 
> > > But if you want anonymity then that's what you want to use because you 
> > > won't have to keep track of any session keys.
> > 
> > In 1.3.x you can do -r for regular recipients,, and -R for hidden
> > recipients, and mix them however you please.
> JFTR, AIUI --throw-keyid still does not clean the message of all traces.
> At least the size of the asymmetric encrypted data would still be
> visible to everybody having access to the ciphertext, which enables them
> to possibly draw conclusions on the size of the modulus.  Even if the
> key is not made public by sending it to keyservers, it would still allow
> some kind of linkability.

This is correct.  The size and the asymmetric algorithm number is
visible.  There are also a lot of hints in a message as to what
version of PGP or GnuPG generated it.

What --throw-keyid does is make the job harder.  There are a whole lot
of "2048-bit RSA keys" out there.  Removing the keyid helps the key
owner to hide in the crowd.

If you use an uncommon key size or key algorithm, the crowd you can
hide in is smaller: there aren't many "3232-bit Elgamal sign+encrypt
keys" out there.

> In short:  don't rely on --throw-keyid to protect your anonymity.

Not by itself, no.  Hidden recipients are intended to make
identification harder, not impossible.

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