Re: [MLS] Use Cases for avoiding Forward Secrecy
Richard Barnes <rlb@ipv.sx> Thu, 01 March 2018 02:21 UTC
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From: Richard Barnes <rlb@ipv.sx>
Date: Wed, 28 Feb 2018 21:21:53 -0500
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To: Dave Cridland <dave@cridland.net>
Cc: mls@ietf.org
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Subject: Re: [MLS] Use Cases for avoiding Forward Secrecy
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Re-adding the list. On Feb 28, 2018 18:21, "Richard Barnes" <rlb@ipv.sx> wrote: > Hey Dave, > > Thanks for the feedback. This is a good point to clarify. It had also > crossed my mind, as the product I work with most in my day job also has > retention features. > > However, I kind of chose not to worry about it, under the following > theory: You can always build a non-forward-secret system out of a > forward-secret one. For example, you could use the FS keys to encrypt a > long-term key, passing it forward across FS boundaries. > > So kind of like Raphael was saying, I figured an application with > history-sharing or retention needs could wrap see extra stuff around MLS to > dial back the appropriate knobs. > > --Richard > > On Feb 28, 2018 12:14, "Dave Cridland" <dave@cridland.net> wrote: > >> Hi folks, >> >> While I'm really pleased to see MLS, and I generally like the idea of >> Forward Secrecy, there's a couple of use cases where it might be worth >> avoiding. Feel free to correct me if these are in fact possible with >> Forward Secrecy. Both these relate to archival access to past >> messages: >> >> * UX - Some users (actually all of them) would like to be able to >> install client software on a new device and have their historical >> messages available to them. Most "business" messaging systems seem to >> work this way, as well as a number of consumer-grade systems. The >> nature of Forward Secrecy means that an archive would need to be held >> on one device and re-sent to another through the network, which is >> trickier to manage, and is reliant on multiple devices being online at >> overlapping times. Alternately, the archival copy might be re-uploaded >> to the server using a static encryption key, I suppose, which would >> rather spoil the point. >> >> * Retention - Many business and government deployments have mandatory >> retention requirements. An example is MIKEY-SAKKE, promoted in part by >> the UK Government for its own communications, which uses mandatory key >> escrow to keep an archived copy of the messages accessible to the >> business units involved. An advantage of the SAKKE system is that it >> allows the key escrow to be offline, limiting attack opportunities. >> >> 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. >> >> None of this is to say that Forward Secrecy should be avoided >> entirely, of course. >> >> Dave. >> >> _______________________________________________ >> MLS mailing list >> MLS@ietf.org >> https://www.ietf.org/mailman/listinfo/mls >> >
- [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