how vulnerable is "hidden-encrypt-to"

[Sin Trenton]

> =====
> 
> The one sending the message really is in control here ;-)
> The sender can use hidden encrypt to ANY public key.
> 
> i.e. if Alice is sending the message and wants to hide her 
> identity,
> nothing prevents her from using throw-keyid with Bob's public key 
> instead of her own, or NIST's, or PGP Corporation's, or any onyone 
> else's.
> 
> If the message is unsigned, the receiver cannot tell,
> (assuming it's sent from an appropriately anonymized e-mail 
> address),
> and if it is signed, then the throw -keyid doesn't hide the 
> sender's identity from the receiver.
> 
> 
> vedaal

I got a bit intrigued by this discussion, having posted a question once
relating to it.

I'm not sure if this input really shows anything or is of any real
contribution to the discussion, but to me it seems all recipients,
including your own are hidden for you when you decrypt a message or a
file? (You get how many keys, but only ID 00000000 for each).
Note that the file was not signed.

So I made a test in my "GPG workshop" (where I have four 'dummy' keys I
created just for testing things out). A file was encrypted with
--hidden-recipients ( -R ); a friend's key, one of my dummy keys [key
four], playing the recipient and sender, plus two keys serving as 'red
herrings', random keys I downloaded from The Guardian (UK newspaper)
and Deutsche Telekom. I then ran a --decrypt and got this output:

gpg: anonymous recipient; trying secret key [key one] ...
gpg: anonymous recipient; trying secret key [key two] ...
gpg: anonymous recipient; trying secret key [key three] ...
gpg: anonymous recipient; trying secret key [key four] ...
gpg: cipher algorithm 122 is unknown or disabled
gpg: anonymous recipient; trying secret key [key one] ...
gpg: anonymous recipient; trying secret key [key two] ...
gpg: anonymous recipient; trying secret key [key three] ...
gpg: anonymous recipient; trying secret key [key four] ...
gpg: anonymous recipient; trying secret key [key one] ...
gpg: anonymous recipient; trying secret key [key two] ...
gpg: anonymous recipient; trying secret key [key three] ...
gpg: anonymous recipient; trying secret key [key four] ...
gpg: anonymous recipient; trying secret key [key one] ...
gpg: anonymous recipient; trying secret key [key two] ...
gpg: anonymous recipient; trying secret key [key three] ...
gpg: anonymous recipient; trying secret key [key four] ...
gpg: okay, we are the anonymous recipient.
gpg: encrypted with RSA key, ID 00000000
gpg: encrypted with RSA key, ID 00000000
gpg: encrypted with RSA key, ID 00000000
gpg: encrypted with RSA key, ID 00000000

/Sin T.