Thunderbird and OpenPGP - Autocrypt

Kai Engert kaie at
Thu Dec 5 11:37:24 UTC 2019

Will Thunderbird support Autocrypt?

Short answer: Thunderbird's implementation will use an approach that is
different from some of the recommendations made in the Autocrypt
specification. However, exchanging messages between Thunderbird and
other clients implementing Autocrypt may be possible, because both use
the OpenPGP standard.

Longer answer:

>From my understanding, the intention of Autocrypt is to make email
encryption as easy as possible, and to automate it as much as possible,
in order to provide protection against passive surveillance.

In order to achieve that, with the current Autocrypt specification
(Level 1), users aren't encouraged to verify the authenticity of the
keys used for encryption with communication partners.

Rather, it is suggested that information contained in arriving plain
text email is used to automatically learn about peer's changed keys, and
to use such updated keys without verification.

Consequently, an adversary who has the technical ability to send an
email in Bob's name, can trick Alice into replacing Bob's key with the
adversary's key, and Alice will use the adversary's key for outgoing
encrypted email to Bob.

With Thunderbird's integrated OpenPGP implementation, we'd like to
assist the user in protecting themselves against active adversaries. We
will not follow the recommendation to automatically replace keys.
Rather, we intend to inform the user about key change events, and
encourage the user to verify the keys used by their communication partners.

While the Autocrypt specification promises to address the active
adversary scenario in a future version of the specification, it is
currently unknown how it will work.

There are some other ideas contained in the Autocrypt specification,
like exchanging keys using email headers, or using a mechanism named
"Gossip" to distribute the set of all public keys of a group
conversation in an unobtrusive way. Thunderbird might implement a subset
of those ideas for some compatibility with other email software that
implements Autocrypt.


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