Re: [openpgp] [openpgp-email] Keyserverless Use of OpenPGP in Email

Ruben Pollan <> Tue, 12 April 2016 14:34 UTC

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To: Simon Josefsson <>, "Vincent Breitmoser" <>
From: Ruben Pollan <>
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Date: Tue, 12 Apr 2016 16:34:30 +0200
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Cc: IETF OpenPGP <>, openpgp-email <>
Subject: Re: [openpgp] [openpgp-email] Keyserverless Use of OpenPGP in Email
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Quoting Simon Josefsson (2016-04-12 15:49:18)
> > To counteract this, we can significantly reduce the number of attached
> > public keys if we are just a little bit clever about the decision of
> > when to add it.  Roughly, it makes sense to attach the public key to
> > the first message of a conversation with each recipient.
> It sounds good in theory, but I don't think that will work.  Let's
> compare how I use e-mail clients.  I use k9, claws, evolution, webmail,
> and probably several other clients that I forgot.  I don't read all
> emails in all clients, of course.  I only read the emails that I need
> in the client I happen to have available.  So if you only include the
> public key in the first message of a conversation, the majority of my
> clients would never see that email because of my usage pattern.  None
> of any newly installed MUA would ever see the email, which over time
> tends to approach 100% of my MUAs since I re-install most of them from
> time to time.
> Now it may be that my usage pattern is a corner case, but I believe it
> is typical for many users today.

In the multi-device world you are describing I think is pretty important to 
share your keyring among your devices, not just your private keys, but all your 
known public keys and your trust on them.

> > Another question is, where to place the key. In email, we have two
> > options: in a separate mime part, or directly next to the pgp
> > signature data.
> You could put it in the email header too.  It would be bizare for
> larger keys, but at least possible in theory.
> Also, the OpenPGP mail/news url field header was intended to provide an
> indirect way to support this:
> You still have some of the keyserver privacy concerns, and require
> a network connection, but I'd just like to mention it as another option
> to consider.

In bitmask we do some of the things you propose Vincent. We attach public keys 
to all sent emails until we get an email encrypted to this public key. We attach 
the key as a mime part, because enigmail already have support for that and is 
one click to import it in your keyring.

We also add the OpenPGP header to all the sent emails and use it to discover 
keys from the 'url' field if it's https and from the same domain than the email 

Even dough I have many concerns about key discovery on the key servers, I think 
we need key servers for key updates. We need to be able to revoke, extend 
expiration, rotate subkeys, ... I think is really important for OpenPGP email 
clients to be able to update periodically the keyring in a 'privacy preserving 
way'. We even dream to have some crappy forward secrecy by rotating encryption 
subkeys often, and deleting them from the keyring.

Ruben Pollan  |
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