Re: [TLS] More clarity on resumption and session hash
Ilari Liusvaara <ilari.liusvaara@elisanet.fi> Tue, 26 May 2015 07:27 UTC
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Date: Tue, 26 May 2015 10:27:24 +0300
From: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
To: Karthikeyan Bhargavan <karthikeyan.bhargavan@inria.fr>
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Subject: Re: [TLS] More clarity on resumption and session hash
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On Tue, May 26, 2015 at 08:17:15AM +0200, Karthikeyan Bhargavan wrote: > On 26 May 2015, at 07:03, Martin Thomson <martin.thomson@gmail.com> wrote: > > > On 25 May 2015 at 10:35, Eric Rescorla <ekr@rtfm.com> wrote: > >> The two main options appear to be: > >> > >> 1. Fall back to a full handshake. > >> 2. Abort the connection > >> > >> The argument for the first appears to be interop. The argument for the > >> second appears to be that it's likely there is an error or a mid-flight > >> reconfiguration on the client (which seems not good). My mild preference > >> is for abort but I think it's important in any case that the draft be > >> clear. > > > > I'd prefer the second two. That is, unless someone can come up with a > > legitimate scenario where the former is needed. > > The feedback we’ve been getting on the draft has been to try and preserve interoperability > with legacy clients and servers (even more than the current draft.) > Considering this goal, aborting seems harsh. Also, there are two dangerous scenarios: - You have non-session_hash session and resume that. - You try to use TLS-Exporter in non-session_hase session for authentication. Based on this, it would seem to be the safest to: - Not offer any non-session_hash sessions for resumption. - Deny resumption (full handshake) of any non-session_hash sessions, regardless of client session_hash support. - Disable TLS-Exporter in non-session_hash sessions. The following are odd edge cases (assuming both ends are due endpoints, these are safe): - Resume session_hash-enabled session wihout session_hash extension - Resume session_hash-enabled session with non-session_hash server. I was thinking latter of those odd behaviours could occur if one performs rolling security fix of server farm: - Client is security fixed - Server A is security fixed - Client connects to A - Client gets session_hash-enabled session. - Client connects to B, attempting to resume. - Servers share session DB/key, so resumption succeeds. - Client gets resumption without session_hash extension. -Ilari
- [TLS] More clarity on resumption and session hash Eric Rescorla
- Re: [TLS] More clarity on resumption and session … Karthikeyan Bhargavan
- Re: [TLS] More clarity on resumption and session … Eric Rescorla
- Re: [TLS] More clarity on resumption and session … Martin Thomson
- Re: [TLS] More clarity on resumption and session … Karthikeyan Bhargavan
- Re: [TLS] More clarity on resumption and session … Ilari Liusvaara
- Re: [TLS] More clarity on resumption and session … Karthikeyan Bhargavan
- Re: [TLS] More clarity on resumption and session … Ilari Liusvaara
- Re: [TLS] More clarity on resumption and session … Ilari Liusvaara
- Re: [TLS] More clarity on resumption and session … David Benjamin
- Re: [TLS] More clarity on resumption and session … David Benjamin
- Re: [TLS] More clarity on resumption and session … Nico Williams
- Re: [TLS] More clarity on resumption and session … Martin Thomson
- Re: [TLS] More clarity on resumption and session … Eric Rescorla
- Re: [TLS] More clarity on resumption and session … David Benjamin
- Re: [TLS] More clarity on resumption and session … Salz, Rich
- Re: [TLS] More clarity on resumption and session … David Benjamin
- Re: [TLS] More clarity on resumption and session … David Benjamin
- Re: [TLS] More clarity on resumption and session … Adam Langley