Re: [TLS] renego, patricide, putting out to stud, etc.

Michael D'Errico <mike-list@pobox.com> Fri, 01 January 2010 01:17 UTC

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Date: Thu, 31 Dec 2009 17:19:09 -0800
From: Michael D'Errico <mike-list@pobox.com>
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Subject: Re: [TLS] renego, patricide, putting out to stud, etc.
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It's not really parent-child, it is actually more like cloning and
metamorphosis.

Mike



Ravi Ganesan wrote:
>  >> OK, but that's a fairly complicated way of describing the semantics. 
> Also
>  >> you used the term "session" to describe the nodes:
> 
> It is somewhat complicated, but I think it is the minimum needed. I just 
> feel getting into connections, sessions, channels, all words which carry 
> unintended baggage, does not seem to be working.  Just consider if I am 
> the Client and you are the Server, and we open a thingy (call it A) 
> communicate for a while. Use A to spawn two more thingys in parallel 
> using abbreviated handshakes (B and C). Then do a renego using full 
> handshake on B (gives us D). D then spawns two more thingys using 
> abbreviated handshakes (E and F). F happens to do a renego using a full 
> handshakes to spawn G. In the meanwhile we do a full handshake renego on 
> A, and then.... you are asked to explain in retrospect exactly what on 
> earth happened. If you use my approach of tagging each of the nodes 
> A,B,C,D,E, F and G with the six variables (session-id, master-secret, 
> client-random, server-random, auth knowledge and RI), and show which of 
> them change from parent to child, you will end up with a compact tree 
> with the properties I mentioned. 
> 
> But of course I am biased, I feel it is limiting to use words that limit 
> TLS to "sockets" or "connections", needlessly.  For instance  what does 
> a connection mean if the binding is not TCP? e.g.  EKR's work on UDP, 
> mine on HTTP, Gajek et al on SOAP).
> This bias aside, however, I think the tree with its state transitions is 
> useful even for regular TLS. Especially since we are keeping chained 
> hashes around.
> 
> 
>     Message: 1
>     Date: Wed, 30 Dec 2009 16:46:49 -0800
>     From: Ravi Ganesan <ravi@findravi.com <mailto:ravi@findravi.com>>
>     Subject: Re: [TLS] sessions, contexts, etc.
>     To: tls@ietf.org <mailto:tls@ietf.org>
>     Message-ID:
>            <3561bdcc0912301646p65923143t1b138fb17b75d9@mail.gmail.com
>     <mailto:3561bdcc0912301646p65923143t1b138fb17b75d9@mail.gmail.com>>
>     Content-Type: text/plain; charset="utf-8"
> 
>     Does something along these lines work as a pedagogical device? Nodes
>     characterized by the parameters of relevance. A root node, three
>     types of
>     ways to spawn a child node. What a child inherits from parent, etc...
> 
>     At the end of a TLS handshake, the Client and the Server share six key
>     pieces of information:
>     (i) a session-id  /*Public information */
>     (ii) a shared master-secret /*Secret. Known only to Client and Server */
>     (iii) the client-random and /* May be public or secret */
>     (iv) the server-random.  /*May be public or secret*/
>     (v) authentication knowledge /* Namely, the Client MAY know that is has
>     authenticated the Server (in practice this almost always is true). The
>     Server MAY know that it has authenticated the Client (relatively rare in
>     practice, but an important sub-category).
>     (vi) renegotiation-information /*The newly introduced RI field at
>     the end of
>     the handshake. */
> 
> 
>     When the  Client and a Server share NONE of the above six pieces of
>     data,
>     the Client will typically initiate a completely fresh session using
>     the FULL
>     handshake.  Such a session is called a ROOT session. A Client and a
>     Server
>     who have completed a ROOT session can engage in further handshakes
>     to create
>     new sessions, which in turn can create further sessions. Treating each
>     session as a node in a graph we can get a tree rooted at the ROOT.
> 
>     Each node can spawn a child node using three different techniques as
>     follows:
> 
>     i) A node can create a child-node by performing an abbreviated
>     handshake.
>     Such an abbreviated-child inherits the session-id, the shared
>     master-secret
>     and the authentication-knowledge, from its parent (these CANNOT
>     change). It
>     gets new client-random, server-random and starts afresh with
>     renegotiation-information.  This technique of spawning a child node is
>     usually used for efficiency considerations (abbrv. handshake
>     requires no PKI
>     operations, which is why it cannot be used to update
>     authentication-knowledge of the other end either).  The creation of
>     such a
>     child-node does NOT result in the previous node becoming inactive.
> 
>     ii) A node can create a child node by performing renegotiation,
>     followed by
>     a full handshake. Such a full-renego-child, starts afresh with new
>     values
>     for all of the first five parameters. The only parameter which keeps
>     it tied
>     to this tree is the renegotiation-information, which is derived from the
>     handshake and the parent-node's renegotiation-information. The primary
>     use-case for this technique is  to update authentication-knowledge
>     of the
>     Server (i.e. does it know who the Client is?).  The creation of such
>     a child
>     node means the parent node can no longer be used.
> 
>     iii) A node can create a child node by performing renegotiation
>     followed by
>     an abbreviated handshake. Such a abbrv-renego-child inherits the
>     session-id,
>     shared-master-secret and authentication-information of its parent.
>     There is
>     a new client-random and server-random, and as in a
>     full-renego-child, the
>     renegotiation-information is derived from the handshake and the the
>     renegotiation-information of its parent.  I do not know why this
>     use-case
>     exists; the encryption/hashing keys change but it is questionable if
>     that
>     adds any protection. The creation of such a child node means the
>     parent node
>     can no longer be used.
> 
>     Observe that each of the different child nodes can give birth to any
>     of the
>     other three types of children.
> 
> 
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