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Internet Engineering Task Force (IETF)                        T. KivinenRequest for Comments: 6467                                     AuthenTecCategory: Informational                                    December 2011ISSN: 2070-1721Secure Password Framework for Internet Key Exchange Version 2 (IKEv2)Abstract   This document defines a generic way for Internet Key Exchange version   2 (IKEv2) to use any of the symmetric secure password authentication   methods.  Multiple methods are already specified in other documents,   and this document does not add any new one.  This document specifies   a way to agree on which method is to be used in the current   connection.  This document also provides a common way to transmit,   between peers, payloads that are specific to secure password   authentication methods.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6467.Kivinen                       Informational                     [Page 1]

RFC 6467           Secure Password Framework for IKEv2     December 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1. Introduction ....................................................22. Method Negotiation ..............................................43. Generic Secure Password Method Payload ..........................64. IKE_AUTH Exchange ...............................................75. Security Considerations .........................................96. IANA Considerations .............................................97. References .....................................................107.1. Normative References ......................................107.2. Informative References ....................................101.  Introduction   The IPsecME working group was chartered to provide for IKEv2   ([RFC5996]) a symmetric secure password authentication protocol that   supports the use of low-entropy shared secrets, and to protect   against off-line dictionary attacks without requiring the use of   certificates or the Extensible Authentication Protocol (EAP).  There   are multiple such methods, and the working group was to pick one.   Unfortunately, the working group failed to pick one protocol, and   there are multiple candidates going forward as separate documents.   As each of those older versions of those documents used a different   technique to negotiate the use of the method and also used different   payload formats, it is very hard to try to make an implementation   where multiple such systems could co-exist.   Current document versions ([SPSK-AUTH], [PACE], and [PAKE]) use the   method described in this document.   This document describes IKEv2 payload formats that can be used for   multiple secure password methods to negotiate and transmit data so   each different method can easily co-exist in the same implementation.Kivinen                       Informational                     [Page 2]

RFC 6467           Secure Password Framework for IKEv2     December 2011   This document consists of two major parts:   o  How to negotiate which secure password method negotiation is used.   o  How to transmit data, between peers, that is specific to secure      password methods.   The secure password methods are not usually meant to be used in the   normal end user (remote access VPN) cases.  In such cases, EAP-based   authentication works fine, and the asymmetric nature of EAP does not   matter.  In such scenarios, the authentication is usually backed up   with the back-end Authentication, Authorization, and Accounting (AAA)   servers and other infrastructure.  That is, in such scenarios,   neither of the IKEv2 peers really knows the secret, as on one end it   is typed in by the user when it is needed, and on the other end it is   authenticated by the back-end AAA server.   The new secure password methods are meant to be used, for example, in   the authentication between two servers or routers.  These scenarios   are usually symmetric: both peers know the shared secret, no back-end   authentication servers are involved, and either end can initiate an   IKEv2 connection.  Note that such a model could also be supported by   EAP when an EAP method that can run in symmetric fashion is in use,   and the EAP method is directly implemented on both peers and no AAA   is in use.   In many cases, each implementation will use only one of the proposed   secure password authentication methods but can include support for   multiple methods even when only one of them will be used.  For   example, a general-purpose operating system running IPsec and IKEv2   and supporting secure password authentication methods to protect   services provided by the system might need to implement support for   several methods.  It is then up to the administrator which one is to   be used.  As the server might need to connect to multiple other   servers, each implementing a different set of methods, it may not be   possible to pick one method that would serve all cases.   The secure password methods mostly keep the existing IKEv2   IKE_SA_INIT exchange and modify the IKE_AUTH authentication step.  As   those methods do not want to add new round trips, negotiating which   of the secure password methods to use needs to happen during the   IKE_SA_INIT.  As the identity of the other end is only provided   inside IKE_AUTH, the responder needs to select the list of supported   methods based only on the IP address of the initiator.  This could   lead to problems if only certain methods would be acceptable for   certain identified peers.  Fortunately, as the authentication is done   based on the secret shared between both peers, the shared secret   should be usable in all of the methods; thus, a remote peer usuallyKivinen                       Informational                     [Page 3]

RFC 6467           Secure Password Framework for IKEv2     December 2011   does not need to restrict selection of the method based on the   initiator's identity but only based on the supported methods and the   administrative policy.   Also, as the initiator already knows which peer it is connecting   with, it can limit which methods it proposes to the other peer.  And   as secure password methods are meant to be used in symmetric cases,   both ends should have similar configuration; i.e., they have the same   shared secret and, most likely, also a list of acceptable   authentication methods to be used.  This could also be interpreted so   that there is no need to support method negotiation, as both ends can   already see this from the configuration.  On the other hand, in most   cases, either end does not really care which method is used but is   willing to use any secure method that the other end supports.  In   such cases, the automatic negotiation provides a way to make the   configuration easy, i.e., no need to pick one method to be used   between the peers.   The reason for using the common IKEv2 payload to transmit, between   peers, data that is specific to the secure password method is that   the payload type field in the IKEv2 is only an 8-bit field, and 62.5%   of the range is already reserved (50% to the private use numbers, and   12.5% to the IKEv1 payload numbers).  This leaves 95 usable numbers,   out of which 16 are already in use.  Initially, it was proposed that   five payload type numbers be consumed.  Those five new payload types   would already represent a 31% increase in the number of currently   allocated payload types.2.  Method Negotiation   Because all of the methods modify the IKE_AUTH exchange, the   negotiation of the secure password method to be used needs to happen   during the IKE_SA_INIT exchange.  The secure password negotiation   exchange would be:   Initiator                         Responder   -------------------------------------------------------------------   HDR(SPIi=xxx, SPIr=0, IKE_SA_INIT,       Flags: Initiator, Message ID=0),       SAi1, KEi, Ni, [N(SECURE_PASSWORD_METHODS)]  -->                      <--  HDR(SPIi=xxx, SPIr=yyy, IKE_SA_INIT,                               Flags: Response, Message ID=0),                               SAr1, KEr, Nr, [CERTREQ],                               [N(SECURE_PASSWORD_METHODS)]Kivinen                       Informational                     [Page 4]

RFC 6467           Secure Password Framework for IKEv2     December 2011   If the N(SECURE_PASSWORD_METHODS) Notify payload is missing, then   normal IKEv2 authentication methods are used.  If the Notify payloads   are included, then the negotiation of the secure password methods   happens inside those payloads.   As it might be possible that future secure password methods will   modify the IKE_AUTH payload in a more substantial way, it is better   that as an end result of the negotiation we have exactly one secure   password method that will be used.  The initiator will know which   methods are usable when talking to that responder, so the initiator   will send a list of acceptable methods in its IKE_SA_INIT request.   The responder will pick exactly one method and put that in its   response.   The secure password methods are identified by the 16-bit IANA-   allocated numbers stored in the Notify payload notification data   field.  If a method supports multiple different password   preprocessing methods, each of those may be allocated a separate   number from this space, or the method might do its own negotiation of   the preprocessing method later.  As the initiator has already   selected the shared secret it will be using, it will also know which   preprocessing it might need, so it should propose only those   preprocessing methods suitable for the selected shared secret.  This   means that it is recommended that separate IANA numbers be allocated   for different preprocessing methods.   The actual Notify payload will look like this:                        1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | Next Payload  |C|  RESERVED   |         Payload Length        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Protocol ID  |   SPI Size    |      Notify Message Type      |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                                                               |   ~                Security Parameter Index (SPI)                 ~   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                                                               |   ~                       Notification Data                       ~   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   The Protocol ID will be zero, and the SPI Size will also be zero,   meaning that the SPI field will be empty.  The Notify Message Type   will be 16424.Kivinen                       Informational                     [Page 5]

RFC 6467           Secure Password Framework for IKEv2     December 2011   The Notification Data contains the list of the 16-bit secure password   method numbers:                        1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | Secure Password Method #1     | Secure Password Method #2     |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | Secure Password Method #3     | ...                           |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   The response Notify payload contains exactly one 16-bit secure   password method number inside the Notification Data field.3.  Generic Secure Password Method Payload   This payload will contain the data that is specific to the secure   password payload.  The IKE_AUTH exchanges might have a number of   these inside, depending on what is required and specified by the   secure password method.  As the secure password method is already   selected during IKE_SA_INIT, there is no need to repeat the   information of the selected secure password method; thus, this   payload only contains the method-specific data.  As some secure   password methods require multiple different payloads, they are   assumed to include their method-specific payload type inside the   payload -- for example, inside the first octet of the data.  However,   this is method-specific, and a method is free to format the payload   data as it wants.   The Generic Secure Password Method (GSPM) payload will look   like this:                        1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | Next Payload  |C|  RESERVED   |         Payload Length        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                                                               |   ~         Data Specific to the Secure Password Method           ~   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   The Payload Type for this payload is 49, and the name used in this   document is "GSPM payload."Kivinen                       Informational                     [Page 6]

RFC 6467           Secure Password Framework for IKEv2     December 2011   If the method uses payload subtypes (which are specific to the secure   password method) inside the GSPM payload, the format will be   like this:                        1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | Next Payload  |C|  RESERVED   |         Payload Length        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |   Subtype*    |                                               |   +-+-+-+-+-+-+-+-+                                               +   |                                                               |   ~         Data Specific to the Secure Password Method           ~   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   * method-specific subtype field   This representation is here only for illustrative purposes; the   secure password method will define the exact format of the payload   contents.4.  IKE_AUTH Exchange   As the negotiation takes place during IKE_SA_INIT, the secure   password methods may modify the IKE_AUTH exchange if needed.  To   easily enable implementing multiple methods, it is recommended that   IKE_AUTH exchange not be modified unnecessarily.  Adding zero, one,   or multiple GSPM payloads to each exchange is needed, as is the   modification to how the AUTH payload is calculated, but all other   changes should be kept minimal.   The IKE_AUTH exchange should look similar to when EAP is used,   meaning that the first request includes IDi, SAi2, TSi, TSr, and some   number of GSPM payloads.  The response should include IDr and, again,   a number of GSPM payloads.  There may be multiple exchanges, each   consisting of some number of GSPM payloads; finally, when   authentication is done, there should be one final exchange where the   request includes the AUTH payload (along with some number of GSPM   payloads) and the response contains AUTH, SAr2, TSi, TSr, and some   number of GSPM payloads.  The number of GSPM payloads is up to the   secure password method but usually will be less than 3.  However,   depending on the method, it might be more.   The AUTH payload calculation should include all the data that would   normally be included, in addition to the extra data needed by the   secure password method.  The secure password method needs to define   how the AUTH payload is calculated.Kivinen                       Informational                     [Page 7]

RFC 6467           Secure Password Framework for IKEv2     December 2011   As the AUTH payload calculation is changed, the secure payload method   should not use any of the existing authentication method numbers in   the AUTH Payload Auth Method field but instead should use the number   allocated in this document.  This number is meant to be used by all   secure password authentication methods.   Initiator                         Responder   -------------------------------------------------------------------   HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH,       Flags: Initiator, Message ID=1),       SK {IDi, [CERTREQ,]           GSPM, [GSPM, ...,]           [IDr,] SAi2,           TSi, TSr}  -->                     <--  HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH, Flags:                                 Response, Message ID=1),                                 SK {IDr, [CERT,]                                     GSPM, [GSPM, ...]}   HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH,       Flags: Initiator, Message ID=2),       SK {GSPM, [GSPM, ...,]}  -->                     <--  HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH, Flags:                                 Response, Message ID=2),                                 SK {GSPM, [GSPM, ...]}   ...   HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH,       Flags: Initiator, Message ID=x),       SK {[GSPM, ...,], AUTH}  -->                     <--  HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH, Flags:                                 Response, Message ID=x),                                 SK {[GSPM, ...,] AUTH, SAr2,                                     TSi, TSr}   Note that the number of the GSPM payloads and other payloads in each   packet will be defined only by the secure password method   documentation, and representations in this document are only for   illustrative purposes.Kivinen                       Informational                     [Page 8]

RFC 6467           Secure Password Framework for IKEv2     December 20115.  Security Considerations   As this document does not describe an exact protocol, the security   considerations are not relevant.  Any secure password method   documentation using payload types described here needs to also   describe the security properties of the protocol it defines or   discusses.6.  IANA Considerations   This document allocates one new IKEv2 message type in the "Notify   Messages Types - Status Types" registry:      16424   SECURE_PASSWORD_METHODS   This document also allocates one new number in the "IKEv2   Authentication Method" registry:      12   Generic Secure Password Authentication Method   This document also adds one new payload type to the "IKEv2 Payload   Types" registry:      49   Generic Secure Password Method      GSPM   This document creates a new IANA registry -- "IKEv2 Secure Password   Methods":      0            Reserved   Values 1-1023 are unassigned.  Values 1024-65535 are for private use   among mutually consenting parties.  Changes and additions to this   registry are done by Expert Review.Kivinen                       Informational                     [Page 9]

RFC 6467           Secure Password Framework for IKEv2     December 20117.  References7.1.  Normative References   [RFC5996]    Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,                "Internet Key Exchange Protocol Version 2 (IKEv2)",RFC 5996, September 2010.7.2.  Informative References   [PACE]       Kuegler, D. and Y. Sheffer, "Password Authenticated                Connection Establishment with IKEv2", Work in Progress,                September 2011.   [PAKE]       Shin, S. and K. Kobara, "Most Efficient Augmented                Password-Only Authentication and Key Exchange for                IKEv2", Work in Progress, July 2011.   [SPSK-AUTH]  Harkins, D.,"Secure PSK Authentication for IKE", Work                in Progress, July 2011.Author's Address   Tero Kivinen   AuthenTec   Eerikinkatu 28   HELSINKI  FI-00180   Finland   EMail: kivinen@iki.fiKivinen                       Informational                    [Page 10]