Re: [Unbearable] FWD: Status of draft-ietf-tokbind-https

=JeffH <Jeff.Hodges@KingsMountain.com> Thu, 16 November 2017 02:42 UTC

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From: =JeffH <Jeff.Hodges@KingsMountain.com>
To: IETF TokBind WG <unbearable@ietf.org>
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Subject: Re: [Unbearable] FWD: Status of draft-ietf-tokbind-https
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From: Leif Johansson <leifj@sunet.se>
Date: Monday, November 13, 2017 at 9:10 PM
To: Eric Rescorla <ekr@rtfm.com>om>, 
"draft-ietf-tokbind-https@tools.ietf.org" 
<draft-ietf-tokbind-https@tools.ietf.org>rg>, "tokbind-chairs@ietf.org" 
<tokbind-chairs@ietf.org>
Subject: Re: Status of draft-ietf-tokbind-https
Resent-From: <alias-bounces@ietf.org>rg>, Leif Johansson <leifj@sunet.se>
Resent-To: <andreipo@microsoft.com>om>, <mnystrom@microsoft.com>om>, Dirk 
Balfanz <balfanz@google.com>om>, Adam Langley <agl@google.com>om>, 
<nharper@google.com>om>, Jeff Hodges <Jeff.Hodges@PayPal.com>om>, 
<draft-ietf-tokbind-https@ietf.org>
Resent-Date: Monday, November 13, 2017 at 9:10 PM

 > On 2017-11-13 14:00, Eric Rescorla wrote:
 > Hi folks,
 > I have made a first pass through this document and while I have some
 > comments it appears generally sound. My one concern is the complexity
 > of the federated version. It's complicated enough that it's not obviously
 > secure and I don't know how much analysis there has been of it.



Have we gotten a secdir review yet? I confess I haven't seen one yet but
I may have missed something...

 > One thing I noticed that is a bit concerning is a potential way for an
 > attacker to get a confused token. As I understand it, the objective of
 > the flow is for the client to get a token which he can provide to the
 > Token Consumer that has in it the TBID for the key which he will use
 > to do a provided token binding to the Token Consumer. However, the
 > Token Provider's notion of who the TC is (the audience) usually comes
 > from some kind of redirect argument.
 > Specifically, consider the case where Alice is for some reason trying
 > to authenticate to the attacker, you can then get the following flow:
 > Alice                        Attacker                  Token Provider
 > Request ------------------------>
 > <-------------  Redirect to TP w/
 > Include-Referred-Token-Binding-ID:true
 > Audience identity = Victim
 > GET ---------------------------------------------------------->
 > EBTMS([K_tp, provided_binding],
 >       [K_attacker, referred_binding])
 > Audience identity = Victim
 > <-------------------------------------------------------- Token
 > So at this point, the Provider issues a token he thinks is for
 > the Victim but actually has the TBID for the attacker. I don't
 > see how to make this an attack, but it seems like it has the TP
 > being confused and (if the token has an audience value in it)
 > a token which is confused too, which doesn't seem ideal. Am I
 > wrong about this?
 > Anyway, my question really is: how can we make sure we have reasonable
 > confidence that this piece of token binding is secure? How much
 > analysis has there been? is there anything I can read? Or do we
 > just have whatever is in the draft?
 > Happy to sync up before the session tomorrow if that's useful
 > Thanks,
 > -Ekr

I don't have anything pressing in the morning. Happy to meet up
to talk about this. JB, Nick and Brian is here but I haven't
seen any of the key folks behind the core protocol yet.

	Cheers Leif