Re: [MLS] Functional Definition of End-to-End Secure Messaging
Alec Muffett <alec.muffett@gmail.com> Fri, 07 May 2021 13:50 UTC
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From: Alec Muffett <alec.muffett@gmail.com>
Date: Fri, 07 May 2021 14:49:58 +0100
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To: Dave Cridland <dave@cridland.net>
Cc: Messaging Layer Security WG <mls@ietf.org>
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Subject: Re: [MLS] Functional Definition of End-to-End Secure Messaging
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Hey Dave! Nice to follow up in long-form. :-) On Fri, 7 May 2021 at 13:51, Dave Cridland <dave@cridland.net> wrote: > As I said on Twitter, I'm hesitant to try to build a one-size-fits-all > definition of "secure". > But that's not what I am trying to do; I am trying to build a one-size-fits-all definition of "end-to-end secure", which is pretty easy to do because there's an inherent threat-model in the phrase "end to end". It comes down to "there are ends. respect them." > I think a much more useful first step (and one where consensus is much > easier to gain) would be to talk about different threats and their > potential mitigations and trade-offs, rather than blanket statements that > things are or are not secure in some absolute sense which I'm unconvinced > exists. > The set of threats is practically infinite, and as we're aware from firewall design it is much more robust to work with an "allowlist" rather than a "blocklist". Hence this approach. > "Secure" is not an absolute > I agree. > and has to be handled in context. > And the context is "end to end", and - especially - "end" is a term that many use and few strictly define. MLS provides a (very) useful set of tools with which to build various > models of secure, including the consumer-grade personal security you appear > to be driving toward. > I am not driving towards anything other than a measurable definition of "end-to-end secure messaging". > The primary objection I have here is that people will make the assumption > that any system that does not conform to your arbitrary definition of > "Secure" is, by inference, "Insecure". > That *is* an objection, however it pivots on the assertion that I am somehow attempting to define "secure" - but I am not. The document clearly states that it is a "Functional Definition of End-to-End Secure Messaging"; perhaps you can suggest how to make that more clear? As an example, ... Your stipulation is that clinicians joining a particular > group chat must not be able to see past messages. This in turn means that > clinicians must be ill-informed about the patient's past, and therefore > there is a heightened clinical risk to the patient. I would argue that > patient safety should be an outcome of an applicable security stance. I > think there is genuine risk involved in providing people with a misleading > single definition of "secure" > That's a great question with a practical use-case, but to me it begs the question of: "why is the system that you [Dave] are describing, appropriate to describe as 'end-to-end secure'?" - who are the ends? Are the messages stored in such a way that they could be accessed by a non-participant, for instance a database administrator? Where is your forward secrecy, and how is what you describe somehow different to (say) a security-hardened version of Facebook Messenger? These are questions which really ought to be asked of *every* platform, and they are *not* being asked, because we have no metric to measure against. Hence this document. This is not to say that your definition is particularly "wrong"; it's not > capable of being wrong for the same reason that it's not capable of being > "right". > I disagree, and I suggest that it is the very nature of your critique which demonstrates the functional requirement for a metric like draft-muffett-end-to-end-secure-messaging - alec -- https://alecmuffett.com/about
- [MLS] Functional Definition of End-to-End Secure … Alec Muffett
- Re: [MLS] Functional Definition of End-to-End Sec… Raphael Robert
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- Re: [MLS] Functional Definition of End-to-End Sec… Dave Cridland
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- Re: [MLS] Functional Definition of End-to-End Sec… Raphael Robert
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- Re: [MLS] Functional Definition of End-to-End Sec… Raphael Robert
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- Re: [MLS] Functional Definition of End-to-End Sec… Raphael Robert
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- Re: [MLS] Functional Definition of End-to-End Sec… Raphael Robert
- Re: [MLS] Functional Definition of End-to-End Sec… Sofía Celi
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- Re: [MLS] Functional Definition of End-to-End Sec… Mallory Knodel
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- [MLS] secure & end Re: Functional Definition of E… Mallory Knodel
- Re: [MLS] Functional Definition of End-to-End Sec… Raphael Robert
- Re: [MLS] Functional Definition of End-to-End Sec… Alec Muffett
- Re: [MLS] secure & end Re: Functional Definition … Alec Muffett