> -----Original Message----- > From: Dan Harkins [mailto:dharkins@xxxxxxxxxx] > Sent: Tuesday, February 05, 2008 12:23 PM > To: Joseph Salowey (jsalowey) > Cc: Dan Harkins; ietf@xxxxxxxx; hokey@xxxxxxxx > Subject: RE: [HOKEY] Last Call: draft-ietf-hokey-erx (EAP > Extensions for EAP Re-authentication Protocol (ERP)) to > Proposed Standard > > > So there's something else besides key name that is used to > identify keys. Great, so that means these hashed key names > are unnecessary. No need to do HMAC-SHA256 to generate a > random string, throw away 3/4 of that result and come up with > something that is unusable. > > Let's get rid of this stuff since it serves no useful > purpose and is computationally expensive. > [Joe] That something else mat not be sufficient to disambiguate keys. For example if MAC address or username is used it is possible that there is more than one session with that entity. > Yes, EAP Session ID (or Username, as Glen suggests) will be > hashed. So if you have an rIK and an rRK and 5 or 6 rMSKs all > derived from the same EMSK then the EAP Session ID (or > Username, as Glen suggests) that identifies that EMSK can be > used as the index in the hash table and all the derivatives > are guaranteed to end up in the same bucket. You look up > based on an identifier on the root and everything is right > there in your hands. If the namespace is completely flat then > searching for all related keys is a pain. > > Dan. > > On Tue, February 5, 2008 12:02 pm, Joseph Salowey (jsalowey) wrote: > > There is nothing in the document that says you must index > keys only by > > key id. I don't really understand the problem here, there is other > > context associated with a key besides a name that can be used for > > indexing. The key name provides a fixed length unique > identifier for > > the key. EAP Session-ID is not fixed length and can be > awkward to use > > in protocols, most likely you will end up hashing it anyway. > > > > Joe > > > >> -----Original Message----- > >> From: ietf-bounces@xxxxxxxx [mailto:ietf-bounces@xxxxxxxx] > On Behalf > >> Of Dan Harkins > >> Sent: Friday, February 01, 2008 5:46 PM > >> To: Dan Harkins > >> Cc: ietf@xxxxxxxx; hokey@xxxxxxxx > >> Subject: Re: [HOKEY] Last Call: draft-ietf-hokey-erx (EAP > Extensions > >> for EAP Re-authentication Protocol (ERP)) to Proposed Standard > >> > >> > >> Hello again, > >> > >> Pardon my repetition but I have come up with a very valid reason > >> why naming keys using HMAC-SHA-256 is a bad idea. > >> > >> If one wants to administratively remove all keys in a particular > >> key hierarchy (which seems like an entirely reasonable > request) one > >> must do a linear search of all keys in all key hierarchies that a > >> particular server maintains! > >> This is because HMAC-SHA-256 has mapped all identifying key > >> information for all key hierarchies to the same name space. > >> It precludes using something like a hash table for fast > lookup of all > >> related keys. > >> > >> If keys were named by concatenating the EAP Session-ID with a > >> string that identified the particular key in the key > hierarchy rooted > >> at the MK derived in that EAP Session-ID then the EAP Session-ID > >> could be used as an index into a hash table and all keys for that > >> particular key hierarchy could be looked up very efficiently. > >> > >> regards, > >> > >> Dan. > >> > >> On Fri, February 1, 2008 5:16 pm, Dan Harkins wrote: > >> > > >> > Hello, > >> > > >> > I believe this is a well organized and complete document. On > >> > numerous occasions while reviewing it I made a mental question > >> > regarding something only to have the question answered in a > >> subsequent > >> > paragraph. > >> > > >> > I do have several comments though: > >> > > >> > 1. this protocol can be used in the presence of AAA proxies. Due > >> > to the nature of AAA proxies a peer or authenticator may not > >> > even know whether they are part of the communication chain. > >> > Therefore, from the view of a security threat their presence > >> > must be assumed by the peer and authenticator. > >> > > >> > The Domain referred to in section 2 (part of the EMSK key > >> > hierarchy draft) specifically allows for proxies as part of > >> > the distributed system of computers that define the Domain. > >> > > >> > This brings up many significant issues that are not addressed > >> > in this draft. > >> > > >> > - It cannot be claimed that a key is being bound to its > >> > context when the context cannot even be scoped. (Section 6) > >> > > >> > - The domino effect is not prevented because compromise of a > >> > proxy will compromise keying material on (other) > >> authenticators. > >> > > >> > - A pairwise key is being given by one of the entities > >> that share > >> > it, e.g. the server, to a 3rd entity, e.g. a proxy, > >> without the > >> > consent of the other peer that shares the key, > e.g. the peer. > >> > This brings up security considerations that are > not discussed. > >> > > >> > - During discussions at a HOKEY meeting and on the list > >> the rationale > >> > that justified proxies was that the peer is more > >> concerned about > >> > receiving network access (which is confirmed in the > >> ERP document > >> > when it says, "The primary purpose [of ERP] is > network access > >> > control.") than about specifically authenticating > >> "the network". > >> > Provided that service is obtained with no surprises > >> in the bill at > >> > the end of the month the rationale was that the peer > >> didn't care > >> > if the key was distributed to proxies if it was > necessary to > >> > continue to provide network access. Which is a > >> reasonable rationale. > >> > But it needs to be mentioned in this document. It > has a unique > >> > threat model that is not discussed anywhere. > >> > > >> > - The aforementioned rationale begs the question of why have > >> > "Domain Specific Keys". If the peer doesn't care > >> whether proxies > >> > have a key, potentially for a different domain, then > >> it doesn't > >> > care about key separation between domains. This is > significant > >> > added complexity for no benefit. > >> > > >> > - RFC4962 REQUIRES things-- bind key to its context, > prevent the > >> > domino effect-- that ERP cannot support. ERP is a AAA key > >> > management protocol though and falls under the scope > >> of RFC4962. > >> > There needs to be justification for why ERP is not > meeting the > >> > mandatory requirements of RFC4962. > >> > > >> > I think all of these issues need addressing before > >> advancement of this > >> > Internet-Draft. > >> > > >> > 2. Inter-Domain ERP > >> > > >> > It is this reviewers recollection that consensus was > >> reached in HOKEY > >> > to require a peer to reauthenticate back to the home AAA > >> server every > >> > time it attached to a POP in different domain. > >> > > >> > Therefore, I wonder why a "Domain-Specific" key, the > >> DSRK, and all it's > >> > progeny-- DS-rIK, DS-rRK, DSUSRK, etc.-- continue to be > >> used by this > >> > protocol. A "HOKEY-KEY", a USRK, should be derived > from the EMSK > >> > and that is the key given, through proxies if need be, > to the ER > >> > server in the visited domain. If the peer goes to a > >> different domain > >> > then it does a full reauthentication resulting in a _new_ > >> USRK, that > >> > has no relation to the previous USRK, being given to > the ER server > >> > in the new domain. Again, it was my understanding that > the group > >> > already reached consensus on this matter. > >> > > >> > 3. HMAC-SHA256 as a key naming technique > >> > > >> > SHA-256 is a computationally intensive operation; > >> HMAC-SHA256 doubly > >> > so. There should, therefore, be some justification to > use such a > >> > strong cryptographic mixing function if all one wants to do is > >> > "uniquely name a key". EAP methods export a > Session-ID. An rIK can > >> > be named by the concatenation of Session-ID and "rIK". > >> Similarly for > >> > the rMSK, rRK and the other keys being generated in ERP. > >> > > >> > This has the added benefit of allowing for key management > >> to quickly > >> > identify keys based on common queries-- all the keys for > >> a specific > >> > Session-ID, or all rIKs held by a particular entity. By using a > >> > strong cryptographic mixing function all specificity of > >> the key names > >> > has been lost across every single key hierarchy that a > >> HOKEY server > >> > may end up managing. > >> > > >> > This is a really bad idea and it should be changed before this > >> > Internet-Draft is advanced. > >> > > >> > 4. Section 5.3.2 EAP-Initiate/Re-Auth Packet > >> > > >> > This packet has the following field: > >> > > >> > +-+-+-+-+-+-+-+-+ > >> > |R|B|L| Reserved| > >> > +-+-+-+-+-+-+-+-+ > >> > > >> > And "R" is, itself, reserved. This makes no sense. Please << 1 > >> > this field. > >> > > >> > regards, > >> > > >> > Dan. > >> > > >> > > >> > > >> > > >> > _______________________________________________ > >> > HOKEY mailing list > >> > HOKEY@xxxxxxxx > >> > http://www.ietf.org/mailman/listinfo/hokey > >> > > >> > >> > >> _______________________________________________ > >> Ietf mailing list > >> Ietf@xxxxxxxx > >> http://www.ietf.org/mailman/listinfo/ietf > >> > > > > > _______________________________________________ Ietf@xxxxxxxx http://www.ietf.org/mailman/listinfo/ietf