Re: [CFRG] A Duck Test for End-to-End Secure Messaging: "Video Deck" on YouTube

Peter Saint-Andre <stpeter@mozilla.com> Fri, 30 July 2021 23:01 UTC

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To: Martin Thomson <mt@lowentropy.net>, cfrg@irtf.org
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From: Peter Saint-Andre <stpeter@mozilla.com>
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Subject: Re: [CFRG] A Duck Test for End-to-End Secure Messaging: "Video Deck" on YouTube
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On 7/29/21 9:02 PM, Martin Thomson wrote:

> This last item highlights a general problem: in many messaging systems, the software that provides protection, the servers, the key management, the authentication systems, and even the protocols involved are all under the control of the same entity.  That entity is generally not included in the set of intended recipients, but they clearly have the power to access the content of messages, should they modify the necessary components.
> 
> You do address this in the sense that you assume the RFC 3552 condition that the endpoint is not compromised.  I think it is worth recognizing that e2e protections like this are often voluntary on the part of system designers.  When they are voluntary, there are still benefits, but not necessarily guarantees.  Often this also relies on operational security practices to provide real outcomes, like ensuring that the team that looks after the servers that forward messages do not have the means to push client updates or to make changes to authentication servers.  
> 
> This was not historically as much of an issue if you assume standardized protocols and independent client implementation, but it is a real concern here.  Either way, making a better distinction about what the TCB is can be critical to understanding where the lines are.   As I hinted at, the TCB also extends beyond the client as it often includes external dependencies for things like trust anchors.  That too will need to be acknowledged and handled carefully.

It might be prudent for this document to mention less centralized
architectural models (and examples other than Signal, WhatsApp, and the
like). For instance, most modern XMPP clients implement OMEMO [1] for
end-to-end encryption and XMPP-based projects like Snikket [2] are
making it much easier for people to deploy XMPP services under their own
control.

Peter

[1] https://xmpp.org/extensions/xep-0384.html

[2] https://snikket.org/