Re: [Atlas] Status Update

[Mirja Kühlewind <[e-mail]>]

Hi Hannes,

see below.

> Am 21.06.2018 um 11:00 schrieb Hannes Tschofenig <[e-mail]>:
> 
> I did a quick read of draft-kuehlewind-taps-crypto-sep-02
> 
> I agree that providing flexibility by separating the transport protocol, record  protocol and control protocol makes sense.
> If you look at the TLS / DTLS protocol you can see that there is much of this already realized today. For example,
>  * Transport: support for various underlying protocols, even non-IP.
>  * Record: DTLS has been used to establish keying material for SRTP and, if you look at network access authentication, also for use with WiFi security. The same is true for some other radio technologies, such as IEEE 802.15.4 in Thread.
> 
> Where the nice separation falls apart a bit (which is not appropriately reflected in the figures) is the unfortunate fact that the handshake protocol itself may need to use some security protection for its own use. In TLS the design just happens in such a way that the record layer is re-used for protecting handshake messages itself (once keys become available). In other protocols, like IKEv2/IPsec there are two separate mechanisms used.

It’s not only the protection but also other transport features, such as reliability. DTLS has its own little transport in that sense. The other option can you use one transport for the handshake and another to actually uses the encryption… from my understanding there are still two problems where things are not as separable as it would nice to have: a) the handshake itself uses the TLS record layer (which is not necessarily a problem but also is not necessary), and b) it’s not only the handshake but also later control messages that would need to be separated (eventually).

> 
> I believe the core message in your document and the message in our document is the same. I have to check how close our Mbed TLS API is to the requirements you outline in your document.

Cool!

> 
> An area where more work is needed IMHO is in the policy context since the developer has to determine which layer has to be protected with what mechanism. This is particularly important when the same protocol can in a flexible way be used at different layers. When you use totally different protocols, as it is often done today then this policy is hardwired.

Another aspect is also when to do what. Because if things are nicely separated and you have session-resumption, you can basically already „pre-load“ crypto context for servers that you know you want to use later.

Mirja


> 
> Ciao
> Hannes
> 
> -----Original Message-----
> From: Atlas [mailto:[e-mail]] On Behalf Of Mirja Kühlewind
> Sent: 19 June 2018 18:53
> To: [e-mail]; Tommy Pauly; Chris Wood
> Subject: Re: [Atlas] Status Update
> 
> Hi all,
> 
> writing as an individual contributor, not an IESG member.
> 
> I just briefly looked at draft-friel-tls-atls-00 and when I saw Figure 6, I have to say that I do wonder a bit what additional standardization is needed here. The new parts are the key export and the App Data Crypto box. However, the key export is mainly an interface question and to my understanding there are by now already libraries that provide the needed interface for quic. And the actual app data crypto should be rather straight forward and probably does not need that much standardization...?
> 
> In the context of taps, however, we've been thinking about how to even more generalize this approach (in figure 6). The two points I think could be generalized here even more are
> 
> 1) The TLS handshake should be completely separated from the crypto and could be run directly by the TLS stack without "tunneling" it through the application. Effectively, in theory the handshake would not even need to use the same transport connection or transport protocol than the application (also it probably could).
> 
> This also something we discuss/propose in this draft as input for taps:
> https://tools.ietf.org/html/draft-kuehlewind-taps-crypto-sep-02
> 
> 2) The TLS handshake could negotiate within one handhshake multiple key shares that can be used on different layers for different protocols and algorithms. I guess that is more a question/request for the TLS working group but goes into the same direction of separating handshake/control and the actual crypto more.
> 
> Mirja
> 
> 
> 
> On 19.06.2018 15:23, Abhijan Bhattacharyya wrote:
>> Hello Hannes,
>> Thanks for the update. The revise charter looks good. So what can we
>> expect in Montral? Do we expect another attempt towards a BoF?
>> I have a view against the particular observation of low activities in
>> the mailing list. I think what ATLAS is trying to do is to collect and
>> coordinate between different relevant stray proposals (which may have
>> already been worked out) under a single consolidated standardization
>> effort. So, the activities are waiting at a threshold of a coordinated
>> future progress. But, more activities in this list is definitely a
>> proposition to establish the point of interest for the IETF community.
>> 
>> With Best Regards
>> Abhijan Bhattacharyya
>> Associate Consultant
>> Scientist, TCS Research
>> Tata Consultancy Services
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>> 
>> -----"Atlas" <[e-mail] <mailto:[e-mail]>>
>> wrote: -----
>> To: "atlas@ietf..org <mailto:[e-mail]>" <[e-mail]
>> <mailto:[e-mail]>>
>> From: Hannes Tschofenig
>> Sent by: "Atlas"
>> Date: 06/08/2018 05:14PM
>> Subject: [Atlas] Status Update
>> 
>> Hi all,
>> 
>> Owen and I submitted another BoF proposal to the IESG based on the
>> feedback from the last IETF meeting.
>> 
>> Here is the most recent charter text we came up with:
>> 
>> ---
>> 
>> There are multiple scenarios where clients and servers need to
>> negotiate shared encryption keys and establish secure, authenticated,
>> integrity-protected, end-to-end encrypted sessions at the application
>> layer over untrusted transport. There are a proliferation of transport
>> protocols and mechanisms in use today across web and IoT use cases
>> including, but not limited to, TCP, UDP, IP, Bluetooth and Zigbee.
>> Additionally, network topologies often include middleboxes and proxies
>> that terminate transport layer connections from clients and
>> re-originate new transport layer connections towards the servers. From
>> the clients and servers perspective, these transport layer proxy
>> functions are untrusted and application data must be protected and
>> encrypted, and not exposed to these proxies. There are multiple
>> potential mechanisms that could be considered for negotiation of
>> encryption keys, and establishment of end-to-end encrypted sessions at
>> the application layer between clients and servers, and this working
>> group proposes use of existing (D)TLS protocols and stacks.
>> 
>> This working group proposes reuse of (D)TLS at the application layer
>> as a simple and straightforward means of achieving the security and
>> implementation goals. The primary purpose of the working group is to
>> develop specifications defining how (D)TLS can be leveraged at the
>> application layer (i.e. Application Layer TLS or ATLS) to establish
>> end-to-end encrypted sessions over a multitude of different transports.
>> 
>> Additionally, during development of ATLS specifications, the working
>> group will consider and address concerns such as:
>> 
>> o complex, multi-hop and lossy transport topologies
>> 
>> o (D)TLS record fragmentation at the transport layer
>> 
>> o middlebox operators whose goals include interception of application
>> layer data
>> 
>> The working group will engage with other relevant working groups
>> across the Applications and Real-Time Area (art), Security Area (sec)
>> and Transport Area (tsv), and one of the goals of this working group
>> is to explicitly identity all related working groups that must be
>> consulted during ATLS specifications development.
>> 
>> ---
>> 
>> There do not seem to be minutes available from the IESG/IAB BoF
>> discussions and how they reached their conclusions. So, we can only
>> report what has been told to us by proxy.
>> 
>> In any case, the IESG rejected the BoF proposal.
>> 
>> The impression from the IESG was that the Bar BOF in London produced
>> mixed feelings and that there was no activity on the list afterwards.
>> 
>> Another comment was that the required standardization effort is too
>> small to justify the setup of an entire working group.
>> 
>> At first, this sounds a bit negative. On the other hand, we have two
>> implementations right now. While they need to be polished I believe
>> this is something we could go forward with.
>> 
>> Ciao
>> Hannes
>> 
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