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Network Working Group                                          L. BlunkRequest for Comments: 2284                                J. VollbrechtCategory: Standards Track                           Merit Network, Inc.                                                             March 1998PPP Extensible Authentication Protocol (EAP)Status of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1998).  All Rights Reserved.Abstract   The Point-to-Point Protocol (PPP) [1] provides a standard method for   transporting multi-protocol datagrams over point-to-point links.   PPP also defines an extensible Link Control Protocol, which allows   negotiation of an Authentication Protocol for authenticating its peer   before allowing Network Layer protocols to transmit over the link.   This document defines the PPP Extensible Authentication Protocol.Table of Contents1.     Introduction ..........................................21.1       Specification of Requirements ...................21.2       Terminology .....................................22.     PPP Extensible Authentication Protocol (EAP) ..........32.1       Configuration Option Format .....................42.2       Packet Format ...................................62.2.1  Request and Response ............................62.2.2  Success and Failure .............................73.     Initial EAP Request/Response Types ....................83.1       Identity ........................................93.2       Notification ....................................103.3       Nak .............................................10Blunk & Vollbrecht          Standards Track                     [Page 1]

RFC 2284                          EAP                         March 19983.4       MD5-Challenge ...................................113.5       One-Time Password (OTP) .........................113.6       Generic Token Card ..............................12   REFERENCES ...................................................13   ACKNOWLEDGEMENTS .............................................14   CHAIR'S ADDRESS ..............................................14   AUTHORS' ADDRESSES ...........................................14   Full Copyright Statement .....................................151.  Introduction   In order to establish communications over a point-to-point link, each   end of the PPP link must first send LCP packets to configure the data   link during Link Establishment phase.  After the link has been   established, PPP provides for an optional Authentication phase before   proceeding to the Network-Layer Protocol phase.   By default, authentication is not mandatory.  If authentication of   the link is desired, an implementation MUST specify the   Authentication-Protocol Configuration Option during Link   Establishment phase.   These authentication protocols are intended for use primarily by   hosts and routers that connect to a PPP network server via switched   circuits or dial-up lines, but might be applied to dedicated links as   well.  The server can use the identification of the connecting host   or router in the selection of options for network layer negotiations.   This document defines the PPP Extensible Authentication Protocol   (EAP).  The Link Establishment and Authentication phases, and the   Authentication-Protocol Configuration Option, are defined in The   Point-to-Point Protocol (PPP) [1].1.1.  Specification of Requirements   In this document, several words are used to signify the requirements   of the specification.  These words are often capitalized.  The key   words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",   "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this document   are to be interpreted as described inRFC 2119 [6].1.2.  Terminology   This document frequently uses the following terms:Blunk & Vollbrecht          Standards Track                     [Page 2]

RFC 2284                          EAP                         March 1998   authenticator             The end of the link requiring the authentication.  The             authenticator specifies the authentication protocol to be             used in the Configure-Request during Link Establishment             phase.   peer             The other end of the point-to-point link; the end which is             being authenticated by the authenticator.   silently discard             This means the implementation discards the packet without             further processing.  The implementation SHOULD provide the             capability of logging the error, including the contents of             the silently discarded packet, and SHOULD record the event             in a statistics counter.   displayable message             This is interpreted to be a human readable string of             characters, and MUST NOT affect operation of the protocol.             The message encoding MUST follow the UTF-8 transformation             format [5].2.  PPP Extensible Authentication Protocol (EAP)   The PPP Extensible Authentication Protocol (EAP)  is a general   protocol for PPP authentication which supports multiple   authentication mechanisms.  EAP does not select a specific   authentication mechanism at Link Control Phase, but rather postpones   this until the Authentication Phase.  This allows the authenticator   to request more information before determining the specific   authentication mechanism.  This also permits the use of a "back-end"   server which actually implements the various mechanisms while the PPP   authenticator merely passes through the authentication exchange.   1. After the Link Establishment phase is complete, the authenticator      sends one or more Requests to authenticate the peer.  The Request      has a type field to indicate what is being requested.  Examples of      Request types include Identity,  MD5-challenge, One-Time      Passwords, Generic Token Card, etc.  The MD5-challenge type      corresponds closely to the CHAP authentication protocol.      Typically, the authenticator will send an initial Identity Request      followed by one or more Requests for authentication information.      However, an initial Identity Request is not required, and MAY be      bypassed in cases where the identity is presumed (leased lines,      dedicated dial-ups, etc.).Blunk & Vollbrecht          Standards Track                     [Page 3]

RFC 2284                          EAP                         March 1998   2. The peer sends a Response packet in reply to each Request.  As      with the Request packet, the Response packet contains a type field      which corresponds to the type field of the Request.   3. The authenticator ends the authentication phase with a Success or      Failure packet.Advantages   The EAP protocol can support multiple authentication mechanisms   without having to pre-negotiate a particular one during LCP Phase.   Certain devices (e.g. a NAS) do not necessarily have to understand   each request type and may be able to simply act as a passthrough   agent for a "back-end" server on a host.  The device only need look   for the success/failure code to terminate the authentication phase.Disadvantages   EAP does require the addition of a new authentication type to LCP and   thus PPP implementations will need to be modified to use it.  It also   strays from the previous PPP authentication model of negotiating a   specific authentication mechanism during LCP.2.1.  Configuration Option Format   A summary of the Authentication-Protocol Configuration Option format   to negotiate the EAP Authentication Protocol is shown below.  The   fields are transmitted from left to right.    0                   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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |    Length     |     Authentication-Protocol   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type      3   Length      4   Authentication-Protocol      C227 (Hex) for PPP Extensible Authentication Protocol (EAP)Blunk & Vollbrecht          Standards Track                     [Page 4]

RFC 2284                          EAP                         March 19982.2.  Packet Format   Exactly one PPP EAP packet is encapsulated in the Information field   of a PPP Data Link Layer frame where the protocol field indicates   type hex C227 (PPP EAP).  A summary of the EAP packet format is shown   below.  The fields are transmitted from left to right.    0                   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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Code      |  Identifier   |            Length             |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |    Data ...   +-+-+-+-+   Code      The Code field is one octet and identifies the type of EAP packet.      EAP Codes are assigned as follows:         1       Request         2       Response         3       Success         4       Failure   Identifier          The Identifier field is one octet and aids in matching          responses with requests.   Length          The Length field is two octets and indicates the length of the          EAP packet including the Code, Identifier, Length and Data          fields.  Octets outside the range of the Length field should          be treated as Data Link Layer padding and should be ignored on          reception.   Data          The Data field is zero or more octets.  The format of the Data          field is determined by the Code field.Blunk & Vollbrecht          Standards Track                     [Page 5]

RFC 2284                          EAP                         March 19982.2.1.  Request and Response   Description      The Request packet is sent by the authenticator to the peer.  Each      Request has a type field which serves to indicate what is being      requested.  The authenticator MUST transmit an EAP packet with the      Code field set to 1 (Request).  Additional Request packets MUST be      sent until a valid Response packet is received, or an optional      retry counter expires.  Retransmitted Requests MUST be sent with      the same Identifier value in order to distinguish them from new      Requests.  The contents of the data field is dependent on the      Request type.  The peer MUST send a Response packet in reply to a      Request packet.  Responses MUST only be sent in reply to a      received Request and never retransmitted on a timer.  The      Identifier field of the Response MUST match that of the Request.         Implementation Note: Because the authentication process will         often involve user input, some care must be taken when deciding         upon retransmission strategies and authentication timeouts.  It         is suggested a retransmission timer of 6 seconds with a maximum         of 10 retransmissions be used as default.  One may wish to make         these timeouts longer in certain cases (e.g. where Token Cards         are involved).  Additionally, the peer must be prepared to         silently discard received retransmissions while waiting for         user input.   A summary of the Request and Response packet format is shown below.   The fields are transmitted from left to right.    0                   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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Code      |  Identifier   |            Length             |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |  Type-Data ...   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-   Code      1 for Request;      2 for Response.Blunk & Vollbrecht          Standards Track                     [Page 6]

RFC 2284                          EAP                         March 1998   Identifier      The Identifier field is one octet.  The Identifier field MUST be      the same if a Request packet is retransmitted due to a timeout      while waiting for a Response.  Any new (non-retransmission)      Requests MUST modify the Identifier field.  If a peer recieves a      duplicate Request for which it has already sent a Response, it      MUST resend it's Response.  If a peer receives a duplicate Request      before it has sent a Response to the initial Request (i.e. it's      waiting for user input), it MUST silently discard the duplicate      Request.   Length      The Length field is two octets and indicates the length of the EAP      packet including the Code, Identifier, Length, Type, and Type-Data      fields.  Octets outside the range of the Length field should be      treated as Data Link Layer padding and should be ignored on      reception.   Type      The Type field is one octet.  This field indicates the Type of      Request or Response.  Only one Type MUST be specified per EAP      Request or Response.  Normally, the Type field of the Response      will be the same as the Type of the Request.  However, there is      also a Nak Response Type for indicating that a Request type is      unacceptable to the peer.  When sending a Nak in response to a      Request, the peer MAY indicate an alternative desired      authentication Type which it supports. An initial specification of      Types follows in a later section of this document.   Type-Data      The Type-Data field varies with the Type of Request and the      associated Response.2.2.2.  Success and Failure   Description      The Success packet is sent by the authenticator to the peer to      acknowledge successful authentication.  The authenticator MUST      transmit an EAP packet with the Code field set to 3 (Success).      If the authenticator cannot authenticate the peer (unacceptable      Responses to one or more Requests) then the implementation MUST      transmit an EAP packet with the Code field set to 4 (Failure).  AnBlunk & Vollbrecht          Standards Track                     [Page 7]

RFC 2284                          EAP                         March 1998      authenticator MAY wish to issue multiple Requests before sending a      Failure response in order to allow for human typing mistakes.         Implementation Note: Because the Success and Failure packets         are not acknowledged, they may be potentially lost.  A peer         MUST allow for this circumstance.  The peer can use a Network         Protocol packet as an alternative indication of Success.         Likewise, the receipt of a LCP Terminate-Request can be taken         as a Failure.   A summary of the Success and Failure packet format is shown below.   The fields are transmitted from left to right.    0                   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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Code      |  Identifier   |            Length             |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Code      3 for Success;      4 for Failure.   Identifier      The Identifier field is one octet and aids in matching replies to      Responses.  The Identifier field MUST match the Indentifier field      of the Response packet that it is sent in response to.   Length      43.  Initial EAP Request/Response Types   This section defines the initial set of EAP Types used in   Request/Response exchanges.  More Types may be defined in follow-on   documents.  The Type field is one octet and identifies the structure   of an EAP Request or Response packet.  The first 3 Types are   considered special case Types.  The remaining Types define   authentication exchanges.  The Nak Type is valid only for Response   packets, it MUST NOT be sent in a Request.  The Nak Type MUST only beBlunk & Vollbrecht          Standards Track                     [Page 8]

RFC 2284                          EAP                         March 1998   sent in repsonse to a Request which uses an authentication Type code.   All EAP implementatins MUST support Types 1-4.  These Types, as well   as types 5 and 6, are defined in this document.  Follow-on RFCs will   define additional EAP Types.      1       Identity      2       Notification      3       Nak (Response only)      4       MD5-Challenge      5       One-Time Password (OTP) (RFC 1938)      6       Generic Token Card3.1.  Identity   Description      The Identity Type is used to query the identity of the peer.      Generally, the authenticator will issue this as the initial      Request.  An optional displayable message MAY be included to      prompt the peer in the case where there expectation of interaction      with a user.  A Response MUST be sent to this Request with a Type      of 1 (Identity).         Implementation Note:  The peer MAY obtain the Identity via user         input.  It is suggested that the authenticator retry the         Indentity Request in the case of an invalid Identity or         authentication failure to allow for potential typos on the part         of the user.  It is suggested that the Identity Request be         retried a minimum of 3 times before terminating the         authentication phase with a Failure reply.  The Notification         Request MAY be used to indicate an invalid authentication         attempt prior to transmitting a new Identity Request         (optionally, the failure MAY be indicated within the message of         the new Identity Request itself).   Type      1   Type-Data      This field MAY contain a displayable message in the Request.  The      Response uses this field to return the Identity.  If the Identity      is unknown, this field should be zero bytes in length.  The field      MUST NOT be null terminated.  The length of this field is derived      from the Length field of the Request/Response packet and hence a      null is not required.Blunk & Vollbrecht          Standards Track                     [Page 9]

RFC 2284                          EAP                         March 19983.2.  Notification   Description      The Notification Type is optionally used to convey a displayable      message from the authenticator to the peer.   The peer SHOULD      display this message to the user or log it if it cannot be      displayed.  It is intended to provide an acknowledged notification      of some imperative nature.  Examples include a password with an      expiration time that is about to expire, an OTP sequence integer      which is nearing 0, an authentication failure warning, etc.   In      most circumstances, notification should not be required.   Type      2   Type-Data      The Type-Data field in the Request contains a displayable message      greater than zero octets in length.  The length of the message is      determined by Length field of the Request packet.  The message      MUST not be null terminated.  A Response MUST be sent in reply to      the Request with a Type field of 2 (Notification).  The Type-Data      field of the Response is zero octets in length.   The Response      should be sent immediately (independent of how the message is      displayed or logged).3.3.  Nak   Description      The Nak Type is valid only in Response messages.  It is sent in      reply to a Request where the desired authentication Type is      unacceptable.   Authentication Types are numbered 4 and above.      The Response contains the authentication Type desired by the peer.   Type      3   Type-Data      This field MUST contain a single octet indicating the desired      authentication type.Blunk & Vollbrecht          Standards Track                    [Page 10]

RFC 2284                          EAP                         March 19983.4.  MD5-Challenge   Description      The MD5-Challenge Type is analagous to the PPP CHAP protocol [3]      (with MD5 as the specified algorithm).  The PPP Challenge      Handshake Authentication Protocol RFC [3] should be referred to      for further implementation specifics.  The Request contains a      "challenge" message to the peer.  A Repsonse MUST be sent in reply      to the Request.  The Response MAY be either of Type 4 (MD5-      Challenge) or Type 3 (Nak).   The Nak reply indicates the peer's      desired authentication mechanism Type.  All EAP implementations      MUST support the MD5-Challenge mechanism.   Type      4   Type-Data      The contents of the Type-Data  field is summarized below.  For      reference on the use of this fields see the PPP Challenge      Handshake Authentication Protocol [3].       0                   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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  Value-Size   |  Value ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  Name ...       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+3.5.  One-Time Password (OTP)   Description      The One-Time Password system is defined in "A One-Time Password      System" [4].  The Request contains a displayable message      containing an OTP challenge.  A Repsonse MUST be sent in reply to      the Request.  The Response MUST be of Type 5 (OTP) or Type 3      (Nak).  The Nak reply indicates the peer's desired authentication      mechanism Type.   Type      5Blunk & Vollbrecht          Standards Track                    [Page 11]

RFC 2284                          EAP                         March 1998   Type-Data      The Type-Data field contains the OTP "challenge" as a displayable      message in the Request.  In the Response, this field is used for      the 6 words from the OTP dictionary [4].  The messages MUST not be      null terminated.  The length of the field is derived from the      Length field of the Request/Reply packet.3.6.  Generic Token Card   Description      The Generic Token Card Type is defined for use with various Token      Card implementations which require user input.   The Request      contains an ASCII text message and the Reply contains the Token      Card information necessary for authentication.  Typically, this      would be information read by a user from the Token card device and      entered as ASCII text.   Type      6   Type-Data      The Type-Data field in the Request contains a displayable message      greater than zero octets in length.  The length of the message is      determined by Length field of the Request packet.  The message      MUST not be null terminated.  A Response MUST be sent in reply to      the Request with a Type field of 6 (Generic Token Card).  The      Response contains data from the Token Card required for      authentication.  The length is of the data is determined by the      Length field of the Response packet.Security Considerations   Security issues are the primary topic of this RFC.   The interaction of the authentication protocols within PPP are highly   implementation dependent.   For example, upon failure of authentication, some implementations do   not terminate the link.  Instead, the implementation limits the kind   of traffic in the Network-Layer Protocols to a filtered subset, which   in turn allows the user opportunity to update secrets or send mail to   the network administrator indicating a problem.Blunk & Vollbrecht          Standards Track                    [Page 12]

RFC 2284                          EAP                         March 1998   There is no provision for retries of failed authentication.  However,   the LCP state machine can renegotiate the authentication protocol at   any time, thus allowing a new attempt.  It is recommended that any   counters used for authentication failure not be reset until after   successful authentication, or subsequent termination of the failed   link.   There is no requirement that authentication be full duplex or that   the same protocol be used in both directions.  It is perfectly   acceptable for different protocols to be used in each direction.   This will, of course, depend on the specific protocols negotiated.   In practice, within or associated with each PPP server, it is not   anticipated that a particular named user would be authenticated by   multiple methods.  This would make the user vulnerable to attacks   which negotiate the least secure method from among a set (such as PAP   rather than EAP).  Instead, for each named user there should be an   indication of exactly one method used to authenticate that user name.   If a user needs to make use of different authentication methods under   different circumstances, then distinct identities SHOULD be employed,   each of which identifies exactly one authentication method.References   [1]   Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,RFC 1661, July 1994.   [2]   Reynolds, J. and J. Postel, "Assigned Numbers", STD 2,RFC 1700, October 1994.   [3]   Simpson, W., "PPP Challenge Handshake Authentication Protocol         (CHAP)",RFC 1994, August 1996.   [4]   Haller, N. and C. Metz, "A One-Time Password System",RFC 1938,         May 1996.   [5]   Yergeau, F., "UTF-8, a transformation format of Unicode and ISO         10646",RFC 2044, October 1996.   [6]   Bradner, S., "Key words for use in RFCs to Indicate Requirement         Levels",RFC 2119, March 1997.Blunk & Vollbrecht          Standards Track                    [Page 13]

RFC 2284                          EAP                         March 1998Acknowledgments   This protocol derives much of its inspiration from Dave Carrel's AHA   draft as well as the PPP CHAP protocol [3].  Bill Simpson provided   much of the boilerplate used throughout this document.   Al Rubens   (Merit) also provided valuable feedback.Chair's Address   The working group can be contacted via the current chair:   Karl F. Fox   Ascend Communications, Inc.   655 Metro Place South, Suite 370   Dublin, Ohio  43017   EMail: karl@ascend.com   Phone: +1 614 760 4041   Fax:   +1 614 760 4050Authors' Addresses   Larry J. Blunk   Merit Network, Inc.   4251 Plymouth Rd., Suite C   Ann Arbor, MI  48105   EMail: ljb@merit.edu   Phone: 734-763-6056   FAX:   734-647-3185   John R. Vollbrecht   Merit Network, Inc.   4251 Plymouth Rd., Suite C   Ann Arbor, MI  48105   EMail: jrv@merit.edu   Phone: +1-313-763-1206   FAX: +1-734-647-3185Blunk & Vollbrecht          Standards Track                    [Page 14]

RFC 2284                          EAP                         March 1998Full Copyright Statement   Copyright (C) The Internet Society (1998).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Blunk & Vollbrecht          Standards Track                    [Page 15]