From: Hal <hfinney@shell.portal.com>
Date: Thu, 2 Feb 95 21:15:55 PST
To: cypherpunks@toad.com
Subject: Re: Adding padding to PGP files
Message-ID: <199502030514.VAA24599@jobe.shell.portal.com>
MIME-Version: 1.0
Content-Type: text/plain


From: Nobody@eniac.ac.siue.edu (Anonymous)
> > Date: Thu, 2 Feb 1995 08:48:49 -0800
> > From: Hal <hfinney@shell.portal.com>
> > 
> > It only works on binary ".pgp" public-key encrypted files (not ascii armored
> > files).  So there would be some work needed to make it a really useful tool.
> > 
> > Hal
> 
>   I just tried adding random characters at the end of a pgp ascii
> armoured message.  I had to cut out the checksum, but pgp was able to
> decrypt the message just fine.  So a very simple program (ideally with
> a strong source of random numbers) should be able to pad ascii
> armoured files.

Unfortunately, this approach is easy but doesn't really succeed in adding
undetectable padding.  The PGP message, once the ascii armor is stripped
away, has a byte count in it.  Anyone can de-armor the message and see
that this byte count does not match the size of the file.  So you also
need to bump this byte count to match the added bytes.  That's all my
perl script does that I posted.

Hal