Signature semantics

[vedaal at hush.com]

David Shaw dshaw at jabberwocky.com
wrote on Tue Nov 4 17:58:49 CET 2008 :

> It is not the place of GPG to modify the plaintext.

ok

>GPG should just provide necessary primitives to solve this, 
>and it does:

>gpg --sig-notation 
>"whatever at example.com=I encrypted this to Baker!" 
>--sign --encrypt  blah.txt

>The notation will be hashed into the signature and cannot be 
removed
>without invalidating the signature.

ok,
works nicely,
but needs a user to be reminded to do it ;-)

how about a friendly gnupg reminder prompt:

gpg: you have chosen to sign with 'u' and encrypt to 'r'
gpg: would you like to add a sig-notation "encrypted-to-keyname-r" 
y/n


>All that said, doing this isn't a cure-all.  Alice (the signer 
here)
>may not want her intended target to be public.

then, in that case, 
(where Alice chooses 'n' to the above well-meaning prompt)
how about this as a feature;

when gnupg decrypts and verifies,
if there is a delay of more than 1 minute between signing and 
encrypting,
then gnupg gives the following 'alert':

gpg: message is signed and encrypted
gpg: signature made at time x, encryption made at time y
gpg: duration between signing and encrypting: time z
gpg: please verify with sender, also check time of e-mail sending

now, even if the attacker goes through the trouble of altering his 
computer time-clock to the time of the signature and then encrypts,
there will still be an unmistakable 'suspicious' delay in the e-
mail sending 


vedaal

any ads or links below this message are added by hushmail without 
my endorsement or awareness of the nature of the link

--
Click here to find your roomate.  Search 1000's of available roomates.
http://tagline.hushmail.com/fc/Ioyw6h4erX3HxVZjXoEdVXXcPEngXmDbFclbyT5HN6w3H14Uqq2qMv/