Partial length headers

Hasnain Mujtaba hmujtaba at
Fri Nov 21 20:16:20 CET 2003

Thanks. A couple more questions:

Looking at the pgpdump of an encrypted file, I see that GPG uses the
Symmetrically Encrypted and MDC Packet (tag 18). 

I cannot find this tag in RFC 2440. Where can I get more information on
this tag type and its internal structure? I am trying to understand how
partial length chunks are built. Are these partial chunks nested within
the outer Symm Encrypted and MDC Packet? What is the name of the
outer-most packet? Is it the Symmetrically Encrypted packet? 

-----Original Message-----
From: gnupg-users-bounces at
[mailto:gnupg-users-bounces at] On Behalf Of David Shaw
Sent: Thursday, November 20, 2003 5:50 PM
To: gnupg-users at
Subject: Re: Partial length headers

On Thu, Nov 20, 2003 at 05:28:58PM -0500, Hasnain Mujtaba wrote:
> Hi all,
> Does GnuPG support Partial Length headers, as specified in the OpenPGP
> RFC 2440?


> If so, how can I force GPG to spit out an encrypted packet using
> partial length headers? I have a 1 MB file and I want to encrypt it
> such that the Encrypted Data Packet uses partial lengths. I am
> interested in streaming the encrypted chunks to a third party.

Normally GnuPG chooses partial or not depending on the requirements of
the data (very large files must be partial, other files can be partial
or not).  You can force it to always be partial by giving it the data
via stdin.  That is, instead of doing:
	gpg --encrypt myfile
	cat myfile | gpg --encrypt > output.gpg


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