Re: [openpgp] Combining signature with signer's public key

"Neal H. Walfield" <> Fri, 11 December 2020 09:53 UTC

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Date: Fri, 11 Dec 2020 10:53:32 +0100
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From: "Neal H. Walfield" <>
To: Kai Engert <>
Cc: holger krekel <>,
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Subject: Re: [openpgp] Combining signature with signer's public key
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On Fri, 11 Dec 2020 10:43:11 +0100,
Kai Engert wrote:
> The amount of data that can be transported in an email header is limited.
> For the simple keys that can be generated inside Thunderbird (primary
> key, single subkey for encryption, single used ID), using the
> Autocrypt header could work.
> However:
> - we also allow users to use their complex keys with Thunderbird,
>   which may contain multiple user IDs,

You only need the User ID corresponding to the email address in the
from field, and the current self signature.

>   and contain many certifications,
>   causing the key to be very big

The last I checked gmail doesn't accept mails larger than 25MB.  So,
you'll need a filter if you intend to include everything...  Also, you
have to remember that the email also has content, so you probably
don't want to reserve more than a few MB for the signer's certificate.
In that case, you pretty much have to filter some certificates...

>   The Autocrypt header seems like an incomplete key distribution
>   mechanism for complex keys.

Indeed.  I'd argue that that is a feature, not a bug.