Hi Bernard, Yoshi, Following up on Lakshminath's suggestions, here are some changes we can incorporate in the draft to move it forward. * Expected lower layer behavior - we will add a paragraph that emphasizes that the lower layer must negotiate the use of GEE between the peer and authenticator. It is necessary that the lower layer indicate that the message type is GEE and not EAP. If such a message type is not supported by the authenticator/peer, it will not be able process those packets. So, there should be no confusion in processing GEE packets as EAP packets by the lower layer. We will clarify this behavior in the additional text. * Expected EAP behavior - GEE does not need any modifications to EAP. The presence/absence of GEE is only handled by the lower layer. Perhaps the figures are misleading - we can delete the figures as I don't think they are adding much value anyway. We can make it clearer in the text that this is not attempting to change any EAP behavior, if that is not clear. * EAP lower layer and GEE - Bernard's review pointed out that the EAP lower layer transport requirements are not discussed in the GEE draft. GEE is not an EAP lower layer. GEE is a protocol that the EAP lower layer can use to allow multiple parallel authentications. Also, this is not quite the same as pre-authentication, since GEE is to allow multiple authentications for different purposes (e.g., device and user; specific types of accesses, say, IPv4 and IPv6, etc.). Pre-authentication, as Lakshminath points out, can still be done with GEE and in fact, multiple types of authentications can be done as pre-authentication. * Packet modification attacks - Bernard raised a question on packet modification attacks leading to, say, Type 2 access being granted, when only Type 1 authentication had occurred. Such MiTM attacks are not a problem when appropriate key/identity binding requirements are met as documented. OTOH, if the peer is malicious, it may try to use Type 1 credentials for Type 2 authentication or vice-versa. However, any time a system expects multiple types of authentication, the authorization information must be clearly sent from the backend server to the authenticator, indicating the type of access the peer can be granted. This is a need for multiple authentications with or without GEE. We can add some text about this in the security considerations section to clarify the required authorization information from the backend to the authenticator. * Identity binding - Bernard points out the incorrect usage of peer IDs in page 12. We will remove the text under "Single Access Control Enforcement with Protected Result Indication" - when both methods are key generating, the MSKs should be bound anyway. * On using CUI for identity binding - I think Bernard raises a good point here. Perhaps, that doesn't make sense as an example and perhaps should be removed. Jari, thoughts on this? We will fix the terminology and other nits suggested by Bernard as we revise the document. Thanks, Vidya > -----Original Message----- > From: Lakshminath Dondeti [mailto:ldondeti@xxxxxxxxxxxx] > Sent: Wednesday, December 27, 2006 11:44 PM > To: Bernard Aboba; Yoshihiro Ohba > Cc: Jari Arkko; Barany, Pete; ietf@xxxxxxxx > Subject: Re: IETF last call on draft-barany-eap-gee-04.txt > > Hi Bernard, Yoshi, > > Many thanks for your reviews and notes. I am going to try > and address the overarching issues. Once we settle on those, > we can take care of the details. > > * On the use of the term "generic": > At the beginning of the GEE standardization effort, the idea > was to specify the protocol and allow use of it by any EAP > lower layer, irrespective of which standards body develops > the lower layer. Upon Jari's suggestion, we introduces the > term 3GPP2 so as it stands now, GEE is only applicable to EAP > lower layers defined by 3GPP2. Please note that *multiple* > lower layers specified by 3GPP2 may use it. Furthermore, the > intended status is "experimental." The idea is to try it out > and if all goes well, allow the protocol to be used by any > lower layer. Finally, the mechanism over the period of 1 > year or so has been known as GEE, so we would like to > continue to use that term. > > * On correctly parsing the GEE header: > Indeed EAP lower layers (would have to) specify how a peer > and an authenticator can negotiate whether to use EAP or GEE > (and versions within GEE etc); after that though, there would > not be any incorrect parsing of a GEE header as an EAP header. > > Perhaps it is best to specify that this is expected of the > EAP lower layer in the GEE I-D. Would that resolve this concern? > > * On specifying GEE at the IETF: > Surely, GEE could have been specified as part of the EAP > lower layer, but that would mean each lower layer would have > to specify it independently and as with most things, those > sort of exercises tend to end up with results slightly (or > vastly, take your pick) different from each other. > > Next, where as it is true that pre-authentication does allow > multiple EAP conversations to occur in parallel, it is > important to note that pre-authentication merely solves a > subset of the problems. In fact, there is nothing to say > that pre-authentication cannot be used with GEE. It can very > well be used. > > (Also please see the explanation for the use of the term > "generic" on why GEE is better specified at the IETF). Jari > also provides a justification for this in his latest email. > > * On getting an expert review of 3GPP2's EAP lower layers by the IETF: > As it turns out, Vidya suggested this very thing at the > beginning of the GEE standardization effort to some of our > 3GPP2 colleagues. The decision of course will be made by > 3GPP2 (the IESG can send an LS of course). 3GPP2 may develop > one or more EAPoBlah standards and we can try and suggest to > them that a review by the IETF in each case would be > worthwhile. In the same vein, it appears that with GEE they > have identified a piece of common functionality that they > think is best specified at the IETF. > > Once we agree on the above issues, we can move forward and > discuss things like key binding, how authenticators might > keep track of results from the multiple authentications etc. > Thanks also for your notes on inconsistencies (e.g., upside > down layering diagram) and gaps in explanations. We will fix > those as part of the next revision of the draft. > > Thanks again for your review and best wishes for the new > year, Lakshminath > > At 05:00 PM 12/24/2006, Bernard Aboba wrote: > >Review of draft-barany-eap-gee-04.txt > > > >Overall Comments > > > >The title of this document "3GPP2 Generic EAP Encapsulation (GEE) > >Protocol" is somewhat of a contradiction in terms, implying both a > >mechanism that is specific to 3GPP2, as well as a "generic" > >encapsulation, suitable for use with any link layer. > > > >This contradiction carries through much of the document, leaving the > >reader uncertain whether the authors are describing a 3GPP2-specific > >lower layer encapsulation of EAP, or a more general > mechanism that is > >intended for use with *all* existing EAP lower layers. > > > >If the document is intended to describe an EAP lower layer, then it > >should not contain language suggesting that EAP peer and > authenticator > >implementations need to be modified for use with GEE, or > diagrams that > >show GEE sitting above the EAP lower layer. > > > >The problem with a generic EAP shim is that the architecture > described > >in RFC 3748 does not provide a mechanism for negotiation of its use, > >and therefore there is no generic (e.g. non-link layer specific) way > >for backwards compatibility to be maintained. > > > >As a result, introducing a shim as described in this > document requires > >modification to existing EAP lower layers, or it risks introducing > >interoperability problems within existing implementations. > No existing > >EAP lower layer has been defined to handle the GEE header, > and if such > >a header were to blindly inserted, it would be interpretted > it as the > >EAP Packet Code field by existing EAP peers, authenticators and > >servers: > > > > 0 1 2 3 4 5 6 7 > > +-+-+-+-+-+-+-+-+ > > |Version|TID|RFL| > > +-+-+-+-+-+-+-+-+ > > > >The version field = 0, and the TID field = 00/01. The RFL bits are > >= 10 or 00. > >Given this, the GEE header would be interpreted as one of > the following > >EAP Packet Code values: > > > >0 (TID = 0, RFL = 00) (Reserved in RFC 3748) > >2 (TID = 0, RFL = 10) (Response, in RFC 3748) > >4 (TID=01, RFL = 00) (Failure, defined in RFC 3748). > >6 (TID=01, RFL=10) Not defined in RFC 3748. > > > >RFC 3748-conformant EAP implementations would be likely to silently > >discard Packet Codes of Types 0 and 6, and would also > discard Code 2 if > >sent by an EAP authenticator and Code 4 if sent by an EAP peer. > > > >While the document states that conforming implementations are to add > >and strip off the GEE header, it is not made clear how use > of EAP GEE > >is negotiated so that EAP peer and authenticator implementations can > >tell if it is being used or not. Presumably this negotiation is to > >occur in the link layer, but since no existing EAP link > layers support > >such a negotiation, and the document does not describe how > it works, I > >am not clear about whether backward compatibility is being > maintained or not. > > > >Given that link layer negotiation seems to be required and > no existing > >link layer supports such a negotiation, GEE appears > incompatible with > >existing EAP lower layers other than perhaps 3GPP2. > > > >A generic shim that only (maybe) works with a single link layer is > >somewhat of a contradiction. > > > >Given the problems of a generic EAP shim, the document makes > much more > >sense if it is viewed as part of a definition of a 3GPP2 lower layer > >for EAP. Presumably 3GPP2 has defined a mechanism by which > the use of > >GEE can be negotiated, and once this is done, 3GPP2 peers and > >authenticators can encapsulate and decapsulate EAP packets within a > >3GPP2 lower layer including the GEE header. This kind of > >encapsulation/decapsulation is described in RFC 3748 as part of the > >operation of a lower layer, so inclusion of GEE within the > 3GPP2 lower > >layer definition makes much more architectural sense. > > > >However, given the current orientation of the document, significant > >rework would be required to recast the GEE scheme as a > 3GPP2-specific > >lower layer definition. Currently the document does not really get > >into sufficient detail to understand exactly how EAP is to be > >encapsulated when run over 3GPP2. For example, there is no > discussion > >of lower layer requirements for transport of EAP packets, as > discussed > >in RFC 3748, Section 3.1. > > > >Specific Comments > > > >Abstract > > > > This document specifies the 3GPP2 Generic EAP Encapsulation (GEE) > > protocol for differentiating between multiple EAP > conversations between > > a peer and an authenticator. > > > >As noted earlier, this paragraph presents GEE as a generic update to > >the EAP specification when it seems more appropriate as part > of a 3GPP2 > >lower-layer definition. > > > > As CDMA2000 third generation cellular networks evolve > [8], [9], EAP > > will also be used as a general authentication protocol that runs > > directly over the data link layer [10]. > > > >Is GEE support included in reference [10]? I presume that > it is, since > >otherwise, I don't see how the mechanism described in the document > >could be deployed. > > > > EAP can be used for different types of authentication, > where multiple > > providers provide access to different services. > However, EAP itself > > does not have the ability to differentiate between multiple EAP > > conversations between a peer and an authenticator. > > > >In general, differentiation between conversations is the task of the > >lower layer, so this is not an EAP architectural issue. > > > > This document specifies the 3GPP2 Generic EAP Encapsulation (GEE) > > protocol for differentiating between multiple EAP conversations > > between a peer and an authenticator. In the rest of > this document, > > we refer to this protocol as GEE, Version 0 or GEEv0. > > > >Given the title of the document, I was expecting something > more along > >these lines: > > > >This document defines a mechanism implemented as part of the 3GPP2 > >lower layer support for EAP defined in [10] which enables > >differentation between multiple EAP conversations occuring > over a 3GPP2 link layer. > >As a result, the mechanism described in this document is specific to > >3GPP2 and is not applicable to other EAP lower layers. > > > > Figure 1 shows an example of the case where the access network > > provider is different from the service network provider. The ANP > > hosts the Authenticator (NAS or Network Access Server in > the figure) > > and an Authentication Server (AAA-ANP in the figure). > The SNP may > > have its own Authentication Server (AAA-SNP in the figure). > > > >This figure implicitly assumes use of an EAP lower layer > that enables > >multiple EAP conversations to be ongoing at the same time. Not all > >existing EAP lower layers permit this. For example, WPA does not > >support pre-authentication or make-before-break, and therefore EAP > >authentication is only permitted between a STA and an AP that it has > >successfully associated to. A STA can only be associated to > a single AP > >within an ESS (associations to separate ESSes are possible via > >multi-net). As a result, I would suggest that the lower > layer assumptions be stated. > > > > When a peer is performing multiple EAP > > authentications, it is not possible to clearly > differentiate between > > the two types of authentications using available means... > > Hence, there is no available means to allow multiple EAP > > authentications for a given peer to occur in > > parallel. > > > >Some existing EAP lower layers do enable an EAP peer to conduct > >multiple EAP authentications in parallel. For example, a STA > >supporting WPA2 pre-authentication can initiate multiple > simultaneous > >EAP authentications (to different BSSIDs). > > > > While EAP methods are TLV-based and can easily be > extended to carry > > additional information between the peer and the server, > EAP itself > > does not provide a means to carry any additional > information between > > the peer and the authenticator. > > > >Not all EAP methods are TLV based, and as described in RFC 3748, the > >lower layer can also carry "additional information" such as a GEE > >header. > > > > It is important that the EAP peer > > and authenticator be able to differentiate between the access and > > service authentication exchanges for multiple reasons. > For example, > > it allows proper routing of the messages to the appropriate EAP > > server and allows the two exchanges to happen in parallel. > > > >EAP peers and authenticators already do this today, as noted > earlier. > >However, this does not relate to routing of EAP packets to > EAP servers; > >that is handled via the EAP Identity Request/Response mechanism as > >described in RFC 3748 and 3579. > > > > Hence, the primary motivation for this document is to provide the > > functionality for EAP peers and authenticators to differentiate > > between multiple EAP exchanges that a peer may be executing in > > parallel to gain access to different networks or services. > > > >As described above, the title suggests that the motivation is to > >describe a 3GPP2-specific EAP lower layer encapsulation. > > > > > >relate t routing of EAP messages to EAP servers. That routing is > >handled uthenticator > > +-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+ > > | | | | | | > > | EAP method| EAP method| | EAP method| EAP method| > > | Type = X | Type = Y | | Type = X | Type = Y | > > | V | | | ^ | | > > +-+-+-+-!-+-+-+-+-+-+-+-+ +-+-+-+-!-+-+-+-+-+-+-+-+ > > | ! | | ! | > > | EAP ! Peer layer | | EAP ! Auth. layer | > > | ! | | ! | > > +-+-+-+-!-+-+-+-+-+-+-+-+ +-+-+-+-!-+-+-+-+-+-+-+-+ > > | ! | | ! | > > | EAP ! layer | | EAP ! layer | > > | ! | | ! | > > +-+-+-+-!-+-+-+-+-+-+-+-+ +-+-+-+-!-+-+-+-+-+-+-+-+ > > | ! | | ! | > > | GEE ! layer | | GEE ! layer | > > | ! | | ! | > > +-+-+-+-!-+-+-+-+-+-+-+-+ +-+-+-+-!-+-+-+-+-+-+-+-+ > > | ! | | ! | > > | Lower ! layer | | Lower ! layer | > > | ! | | ! | > > +-+-+-+-!-+-+-+-+-+-+-+-+ +-+-+-+-!-+-+-+-+-+-+-+-+ > > ! ! > > ! ! > > +------------>-------------+ > > > > > > Figure 2: GEE Protocol stack and Peer to Authenticator > interaction > > in > > > >In this diagram, GEE should be included as part of the lower layer, > >rather than a distinct entity below the EAP layer, given that GEE > >cannot function without modifications to the lower layer. > > > > Peer Pass-through Authenticator Authentication > > Server > > +-+-+-+-+-+-+ +-+-+-+-+-+-+ > > | | | | > > |EAP method | |EAP method | > > | V | | ^ | > > +-+-+-!-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-!-+-+-+ > > | ! | |EAP | EAP | | | ! | > > | ! | |Peer | Auth.| EAP Auth. | | ! | > > |EAP ! peer| | | +-----------+ | |EAP !Auth.| > > | ! | | | ! | ! | | ! | > > +-+-+-!-+-+-+ +-+-+-+-!-+-+-+-+-+-!-+-+-+-+ +-+-+-!-+-+-+ > > | ! | | ! | ! | | ! | > > |EAP !layer| | EAP !layer| ! | | ! | > > | ! | | ! | EAP ! layer | | EAP !layer| > > +-+-+-!-+-+-+ +-+-+-+-!-+-+-| ! | | ! | > > |GEE !layer| | GEE !layer| ! | | ! | > > +-+-+-!-+-+-+ +-+-+-+-!-+-+-+-+-+-!-+-+-+-+ +-+-+-!-+-+-+ > > | ! | | ! | ! | | ! | > > |Lower!layer| | Lower!layer| AAA ! /IP | | AAA ! /IP | > > | ! | | ! | ! | | ! | > > +-+-+-!-+-+-+ +-+-+-+-!-+-+-+-+-+-!-+-+-+-+ +-+-+-!-+-+-+ > > ! ! ! ! > > ! ! ! ! > > +-------->--------+ +--------->-------+ > > > >This diagram is also problematic because the kind of decapsulation > >described here can only be carried out by an EAP lower layer, not > >within the EAP layer itself. If GEE is included as part of > the lower > >layer, then the diagram makes more sense, since it would be > clear that > >GEE requires lower layer modifications. > > > > When the authenticator operates in pass-through mode, > the GEE layer > > terminates at the authenticator and the EAP packet is sent over a > > backend AAA layer (e.g., RADIUS [11]). In this case, the > > authenticator must handle the GEE fields in exactly the > same manner > > as in the multiplexing model. The fields in the GEE > header may be > > used by the authenticator to identify the correct EAP exchange to > > properly route the EAP packet. A Transaction ID (TID) > field defined > > in the protocol allows the EAP exchanges to be > distinguished. The > > TID field is used to look up the appropriate domain to which a > > particular EAP message must be routed. > > > >As described in RFC 3748, the behavior described above can only be > >satisfied by an EAP lower layer, since a legacy EAP > implementation will > >not know how to add or strip a GEE header. So the term "GEE-enabled > >lower layer" would be more appropriate than "GEE layer". > > > > Depending on the architecture, the authenticator that is > responsible > > for each authentication may be different. This could be true > > irrespective of whether the EAP server is the same or > different for > > each authentication. However, in most practical cases, > the need for > > multiple authentications arises only when the EAP > servers performing > > the different types of authentications are different. > Figure 4 shows > > the architecture with each provider having a different > authenticator > > that is engaged in different EAP exchanges that the peer > performs. > > In 3GPP2 networks, single authenticator and multiple > authenticator > > architectures are both possible. > > > >Since existing EAP lower layers already support multiple > simultaneous > >authentications with different authenticators (and different EAP > >servers), this scenario can be realized today, without the > GEE header. > > > > Since GEE runs between the peer and the authenticator, > it brings a > > slight variance when the authenticator for each EAP exchange is > > different. Since the multiple EAP authentications are > over the same > > link, the EAP exchange between the peer and one of the > authenticators > > may have to pass through another authenticator or > enforcement point. > > Hence, the lower layers at each hop in this case must be able to > > indicate the presence of the GEE header. > > > >Actually, the lower layer *always* needs to support the GEE > header, right? > > > > --------------------------------- > > | | > > | Data link layer header | > > | | > > --------------------------------- > > | | > > | GEE header | > > | | > > --------------------------------- > > | | > > | EAP packet | > > | | > > --------------------------------- > > > >This diagram is upside down (other diagrams put EAP layer on > top of the > >GEE layer). > > > > Version > > > > The first 4 bits in the GEE header represent the > protocol version > > number. This field MUST be set to 0 for GEEv0. > > > > Transaction ID (TID) > > > > A 2-bit TID flag is used to distinguish between multiple EAP > > conversations. In Version 0 of GEE (GEEv0), the TID > field MUST be > > either 00 or 01. When TID = 01, the encapsulated EAP > packet is > > for Type 1 authentication. When TID = 00, the > encapsulated EAP > > packet is for Type 2 authentication. In GEEv0, TID > values other > > than 00 and 01 are reserved and MUST NOT be used. > > > >Why are 4 bits used for the Version, but only 2 for the > transaction ID? > >Existing EAP lower layers can handle more than 4 simultaneous EAP > >authentications, so that a two bit transaction ID seems to provide > >*less* flexibility than already exists. > > > > Result flags/code (RFL) > > > > The last 2 bits in the GEE header are used to > indicate the result > > of the EAP authentication in progress. The leftmost > bit in this > > field is the 'K' bit and indicates whether the MSK > resulting from > > the EAP conversation being encapsulated by the particular GEE > > session must be bound with an MSK resulting from the > second EAP > > conversation carried in a second GEE session. If set, this > > implies that the peer MUST bind the MSKs to derive TSKs. The > > process of MSK binding is described in Section 5.3. > In GEEv0, the > > last bit is the R bit and is reserved and MUST be set > to zero at > > the sender and MUST be ignored by the receiver. > > > >Statements about the use of an MSK only really make sense > within the a > >lower layer definition, since presumably the EAP method will > output the > >MSK/EMSK as it would normally, with no awareness that GEE is being > >used. > > > > When the peer receives a GEEv0 packet, the TID field in the GEEv0 > > header MUST be used to determine if the encapsulated EAP > packet is > > for Type 1 or Type 2 authentication. If TID value is 01 in the > > packet received from the authenticator, the peer must perform the > > necessary Type 1 authentication. For instance, this may > mean that > > the peer provides the appropriate identity and use the > appropriate > > EAP method in the EAP session. When the TID is set to 00 in the > > packet received from the authenticator, the peer must perform the > > necessary Type 2 authentication. > > > >At first glance, this appears to be a statement about EAP packet > >handling. I would rephrase it to say "when a 3GPP2 lower layer > >receives a GEEv0 packet... if the enapsulated 3GPP2 frame is > for Type 1 > >or Type 2 authentication... the 3GPP2 lower layer must perform the > >necessary Type 1 authentication..." > > > >5.2. Packet Handling at the Authenticator > > > > When the authenticator receives a GEEv0 packet, the TID > value in the > > header MUST be used to determine if the encapsulated EAP > packet is > > for Type 1 or Type 2 authentication. > > > >Again, I don't believe that this document should be modifying EAP > >authenticator behavior described in RFC 3748. This should > be modified > >to say "when the 3GPP2 lower layer residing on the authenticator > >receives..." > > > >5.3. Multiple authentications and access control enforcement > > > > When both Type 1 and Type 2 authentications are carried > out, access > > control MUST conform to the following cases. > > > > > > Type1 Type2 Combined result > > > > Case 1 Success Success Success > > Case 2 Success Failure Type1 > related access only > > Cases 3&4 Failure S/F Failure > > Cases 5&6 N/A S/F S/F > > > >This diagram suggests that network access can be granted > even if one of > >the authentications fail. If the GEE header is not > protected (it would > >be hard to protect unless it represented a > re-authentication, since no > >keys have been derived), this seems like it could result in > a privilege > >elevation attack. For example, unless the NAS kept track of which > >conversation related to which GEE header, an attacker could > potentially > >modify the GEE header in transit, resulting in granting a different > >Type of access than was intended. For example, the attacker could > >modify a GEE Type 1 to a GEE Type 2, etc. > > > > GEE requires that at least one of the authentications to be key > > generating and both authentications to be mutually > authenticating. > > > >How does GEE enforce this requirement? If GEE is part of the lower > >layer, then it makes more sense to say "3GPP2 lower layers > require that > >at least one...". > > > > If one of the authentications is not key generating, > then there MUST > > be a way for the authenticator to identify the two authentication > > conversations (Type 1 and Type 2) corresponding to a peer. > > Specifically, there MUST be a mechanism for the authenticator to > > correlate the Type 1 and Type 2 credentials; typically this is > > facilitated by backend network protocol support. An > example of such > > backend support is to be able to send an identifier that > is unique to > > the peer across the authentications in an authenticated > manner. For > > instance, when both authenticators reside in the same > node, the AAA > > transactions may return Chargeable-User-Identity (CUI) attributes > > [12] and the node can compare them for equality. If there is a > > mismatch, or the node has not received such an identity from both > > transactions, the peer MUST be disconnected. > > > >Since different AAA servers can issue different CUIs for the > same user, > >I am not clear how a NAS could compare them. And in any > case, the CUI > >document describes the returned attributes as opaque blobs, no? > > > > MSK Binding > > > > In this case,even when there are multiple authenticators, we > > assume that there is only one access control > enforcement point. > > Here, the combined MSK MUST be used to derive session keys > > (Transient session keys, TSKs). Both authenticators > deliver the > > MSK to the enforcement point and it computes the > combined MSK as > > follows: Combined-MSK = f(MSK-Type 1, "GEE Combined > Key" || MSK- > > Type 2), where f represents prf+ as defined in [3]. > The length of > > the Combined-MSK MUST be 512 bits. With GEEv0, the > PRF is HMAC- > > SHA-256. > > > >The use of terms such as "combined MSK" suggest that this > document is > >updating RFC 3748. I would suggest that a different term be > used, such > >as "Intermediate Key Binding" (IMSK). > > > > Single Access Control Enforcement with Protected Result Indication > > > > In the event that there can be a protected result indication > > between authenticators and/or enforcement points with a way to > > correlate the peer IDs used in the EAP conversations, it is > > feasible to have the TSK generated from only one MSK. A MiTM > > attack may be plausible in this case, and hence it is NOT > > RECOMMENDED. > > > >I'm unclear what this paragraph is intending to say. The > authenticator > >is presumably unable to correlate peer-IDs, given that it is > operating > >in "pass-through" and may not even have visibility into the > EAP method > >exchanges since they are encrypted with keys it does not have access > >to. Does the paragraph mean to imply that the NAS requests > the Peer-Id > >attribute be sent to it by the AAA server? > > > > When two EAP authentications are performed, it is always > feasible to > > use keys from a first exchange to protect a subsequent exchange. > > Note that the two authentications in this case will occur > > sequentially and the first method must be key > generating. The use of > > GEE does not preclude such an operation, even though the main > > motivation for GEE is to allow parallel execution of the EAP > > exchanges. > > > >In fact, existing lower layer specifications *require* that the > >authentications be handled sequentially. For example, in WPA/WPA2, > >receipt of keys kicks off the 4-way handshake. This is > another reason > >why GEE is inherently incompatible with existing EAP lower layers. > > > >6. GEE Extensibility > > > > GEE could be extended to support dynamic TID assignment, where an > > authenticator may pick an unused TID value. The peer could > > participate in as many as 4 EAP conversations in parallel. > > > >As noted earlier, this is already possible. > > > > In order for the peer to be able to understand the > meaning of each > > TID, a new mechanism would be needed to send information about > > authentication type and other policy hints. > > > >Given that existing implementations can already handle multiple > >authentications, I don't understand why "policy hints" need > to be sent > >across the wire. > > > > If the EAP method used for one authentication is known > to be weaker > > than the EAP method used for another authentication, whereas the > > authenticator may intend to enforce one authentication before the > > other, an attacker may modify the GEE flags to cause the peer to > > start the weaker authentication without the protection > of stronger > > authentication. The adversary may then be able to break > the weaker > > authentication method and gain access to services. Even if the > > authenticator requires, say, both Type 1 and Type 2 > authentications > > from all peers, it is plausible for a rogue peer with available > > credentials for Type 1 authentication to gain access to Type 2 > > services for which it does not have proper credentials. > > > >Wouldn't it also be possible for an attacker to gain access to a > >different service type (1 vs. 2) by packet modification? > > > > To mitigate this threat, i.e., when the EAP method used for one > > authentication (e.g., Type 2) is more vulnerable to > attacks than the > > EAP method used for another authentication (e.g., Type 1), the > > authenticator needs to strictly enforce a policy of Type 1 > > authentication first, and require that the Type 2 authentication > > occur within the secure channel established as a result of Type 1 > > authentication. Another possible solution is for the > authenticator > > to maintain an association between the Layer 2 security > association > > and Layer 3 address(es), to prevent rogue peers from > stealing other > > peers' IP services. > > > >The problem is that EAP authentication typically occurs > *before* layer > >3 addresses are assigned, so that this would require the > authenticator > >to snoop on layer 3 traffic occuring after authentication, > as well as > >to keep additional state. > > > > Suppose a peer has credentials for Type 1 authentication > in a visited > > network and credentials for both Type 1 and Type 2 > authentication in > > the home network. It is plausible that the peer may > supply its home > > network credentials for Type 1 as well as Type 2 > authentication and > > thereby avoid any payments to the visited ANP. To avoid this > > possibility, the AAA-ANP may send to the authenticators > its Type 1 > > authentication policy by sending a list of realms for > which Type 1 > > authentication request is allowed to be forwarded to > home network. > > The authenticator may share that information with the > peer in the EAP > > identity request following the semantics in RFC 4284 > [13] or other > > similar procedures. > > > >Since RFC 4284 hints are unprotected, it seems like this would be > >vulnerable to active attack. > > > > There are several possible mitigation strategies > including the use of > > identifier binding between authentications (e.g., Layer > 2 and Layer 3 > > identifier correlation), or in case of sequential > authentications, > > the use of key material from the first authentication to encrypt > > future authentications. Other solutions require all > authentications > > to be key generating and binding all the keys to > generate the master > > key used to bootstrap the traffic key generation process or using > > multiple encapsulations using the generated keys. > > > >As described earlier, this would require authenticators to snoop on > >layer 3 exchanges and keep additional state on EAP peers. > > > >_______________________________________________ > >Ietf mailing list > >Ietf@xxxxxxxx > >https://www1.ietf.org/mailman/listinfo/ietf > > > _______________________________________________ > Ietf mailing list > Ietf@xxxxxxxx > https://www1.ietf.org/mailman/listinfo/ietf > _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf