Re: [MLS] Use Cases for avoiding Forward Secrecy
Dave Cridland <dave@cridland.net> Wed, 28 February 2018 22:56 UTC
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From: Dave Cridland <dave@cridland.net>
Date: Wed, 28 Feb 2018 22:56:22 +0000
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To: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Subject: Re: [MLS] Use Cases for avoiding Forward Secrecy
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On 28 February 2018 at 21:16, Stephen Farrell <stephen.farrell@cs.tcd.ie> wrote: > > Hiya, > > On 28/02/18 17:14, Dave Cridland wrote: >> Given the latter, for example, I could not use an MLS-based system to >> discuss a tax problem with the authority, and since I'm unlikely to >> have a SAKKE-based messaging client, I'm unlikely to have encrypted >> messaging to my tax authority at all - which seems signficantly worse >> than merely having no Forward Secrecy. > > Sorry, why is transport layer security not sufficient between you > and your tax authority? > Because it's not a single hop. Supposing my tax authority uses XMPP, for example, and so has (in my case) hmrc.gov.uk as an XMPP domain. I use some commercialish XMPP provider. I don't want my provider to be able to read my tax messages, nor do I want them archived in plaintext on the server (although I probably do want a verifiable record). Meanwhile, HMRC wants to keep an archived, but secured, copy at their end, viewable by their organisation. > I'm unclear as to why the security guarantees (aimed for) between > groups of people ought be reduced in order to meet the goals of > securing communications between a person and a service provider. > I'm not suggesting they should be. I am suggesting that it might be nice if my options were not simply FS or FO. (Besides which, the archives in a non-FS situation gain some security guarantees, too). > I do agree that it'd be good if a user of some application could > add a new device and still see old messages, but I'm not at all > clear that's that significant (for the crypto) since people will > always need to have some kind of fallback to handle cases where > they've lost state. Assume a FS-only message transfer. In that case, how do we recover missing messages? We have to transport those from another device that has them. That's a perfectly reasonable concept, and one that has been tried before in Skype. Unfortunately, as mobile devices replaced desktop/laptop combinations as the dominant device, they switched away from the design back to centrally-held archives since the clever synchronisation options simply didn't work. Of course, there are users who prefer the trade-off of higher security and no (or limited) archives. Such users would, one hopes, be warned about the change in security should they enter into a conversation with someone who cannot (or will not) support FS. Dave.
- [MLS] Use Cases for avoiding Forward Secrecy Dave Cridland
- Re: [MLS] Use Cases for avoiding Forward Secrecy Raphael Robert
- Re: [MLS] Use Cases for avoiding Forward Secrecy Phillip Hallam-Baker
- Re: [MLS] Use Cases for avoiding Forward Secrecy Stephen Farrell
- Re: [MLS] Use Cases for avoiding Forward Secrecy Phillip Hallam-Baker
- Re: [MLS] Use Cases for avoiding Forward Secrecy Dennis Jackson
- Re: [MLS] Use Cases for avoiding Forward Secrecy Phillip Hallam-Baker
- Re: [MLS] Use Cases for avoiding Forward Secrecy Dave Cridland
- Re: [MLS] Use Cases for avoiding Forward Secrecy Phillip Hallam-Baker
- Re: [MLS] Use Cases for avoiding Forward Secrecy Eric Rescorla
- Re: [MLS] Use Cases for avoiding Forward Secrecy Phillip Hallam-Baker
- Re: [MLS] Use Cases for avoiding Forward Secrecy Dennis Jackson
- Re: [MLS] Use Cases for avoiding Forward Secrecy Jon Millican
- Re: [MLS] Use Cases for avoiding Forward Secrecy Stephen Farrell
- Re: [MLS] Use Cases for avoiding Forward Secrecy Phillip Hallam-Baker
- Re: [MLS] Use Cases for avoiding Forward Secrecy Richard Barnes
- Re: [MLS] Use Cases for avoiding Forward Secrecy Dave Cridland
- Re: [MLS] Use Cases for avoiding Forward Secrecy Dave Cridland
- Re: [MLS] Use Cases for avoiding Forward Secrecy Russ Housley
- Re: [MLS] Use Cases for avoiding Forward Secrecy Phillip Hallam-Baker
- Re: [MLS] Use Cases for avoiding Forward Secrecy Jon Millican
- Re: [MLS] Use Cases for avoiding Forward Secrecy Sean Turner
- Re: [MLS] Use Cases for avoiding Forward Secrecy Dave Cridland
- Re: [MLS] Use Cases for avoiding Forward Secrecy Dave Cridland
- Re: [MLS] Use Cases for avoiding Forward Secrecy Katriel Cohn-Gordon
- Re: [MLS] Use Cases for avoiding Forward Secrecy Dave Cridland
- Re: [MLS] Use Cases for avoiding Forward Secrecy Eric Rescorla
- Re: [MLS] Use Cases for avoiding Forward Secrecy Nadim Kobeissi
- Re: [MLS] Use Cases for avoiding Forward Secrecy Dave Cridland
- Re: [MLS] Use Cases for avoiding Forward Secrecy Stephen Farrell
- Re: [MLS] Use Cases for avoiding Forward Secrecy Dave Cridland
- Re: [MLS] Use Cases for avoiding Forward Secrecy Nadim Kobeissi
- Re: [MLS] Use Cases for avoiding Forward Secrecy Phillip Hallam-Baker