Re: [apps-discuss] HTTP MAC Authentication Scheme

Eran Hammer-Lahav <eran@hueniverse.com> Fri, 20 May 2011 21:25 UTC

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From: Eran Hammer-Lahav <eran@hueniverse.com>
To: Nico Williams <nico@cryptonector.com>
Date: Fri, 20 May 2011 14:18:21 -0700
Thread-Topic: [apps-discuss] HTTP MAC Authentication Scheme
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Cc: "apps-discuss@ietf.org" <apps-discuss@ietf.org>, Ben Adida <ben@adida.net>, "Adam Barth \(adam@adambarth.com\)" <adam@adambarth.com>, "http-state@ietf.org" <http-state@ietf.org>, HTTP Working Group <ietf-http-wg@w3.org>, OAuth WG <oauth@ietf.org>
Subject: Re: [apps-discuss] HTTP MAC Authentication Scheme
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> -----Original Message-----
> From: Nico Williams [mailto:nico@cryptonector.com]
> Sent: Friday, May 20, 2011 1:25 PM
> To: Eran Hammer-Lahav
> Cc: apps-discuss@ietf.org; Ben Adida; http-state@ietf.org; OAuth WG; Adam
> Barth (adam@adambarth.com); HTTP Working Group
> Subject: Re: [apps-discuss] HTTP MAC Authentication Scheme
> 
> Additional comments:
> 
>  - Using nonces for replay protection is heavy-duty.  It is difficult to
> implement a reliable, secure, high-performance replay cache.  (It is easy to
> implement just a high-performance replay cache: use
> memcache.)
> 
>    I recommend an option to use sequence numbers at the server's choice,
> understanding, of course, that requests will not be received in sequence.
> The use of a sliding sequence number window makes it possible to do at
> least as well as when using nonce, and probably faster while still being
> secure.

We switched to use time since credentials were issued. This should be pretty easy to implement if you really need reply protection by using a small window (clock sync is no longer a problem, just the delay in getting the credentials to the client, which should be a small window).

>  - In an open wifi environment active attacks may not be very difficult, thus
> an option to secure more than just a handful of bits from the request, would
> be nice (all of the request and all of the response, say).  The hard part is how
> to decide when to use one or the other.  Ideally browsers can request more
> protection when the network is reconfigured such that there's one or more
> clear wifi interfaces.

There is just no easy way to do that. If you need more, use TLS.

EHL