Split Data Packet into Multiple Packets?

[David Shaw]

On Aug 16, 2010, at 6:24 PM, James Board wrote:

> Hi,
> 
> I looked into the OpenPGP Message Format spec, and some encrypted files, and figured out that no matter how large my encrypted message is, gpg uses a single Data Packet for the cipher text.  Can I somehow split that Data Packet into multiple independent Data Packets and decrypt them independently of each other?  I know I can't do that with standard command-line args to gpg, but I'm willing to manipulate the Data Packet to do this.  Is it possible from a technical standpoint ov view?

Yes and no.  Yes, in that you can probably torture the GPG code into doing it.  No, in that OpenPGP does not permit multiple data packets in a single message.

> Also, what is the format of that Data Packet?  The OpenPGP Message Format is silent on that matter.  I'm not using any compression when I encrypt, so the Data Packet should be about the same size as the unencrypted file.  However, it's usually about 55 bytes longer than that.  What other information is stored in the Data Packet and what is the format?

Read RFC-4880.  Specifically, section 11.3, which gives the various legal packet combinations.

David