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Network Working Group                                            T. Aura
Internet-Draft                                          Aalto University
Intended status: Standards Track                                M. Sethi
Expires: November 25, 2017                                      Ericsson
                                                            May 24, 2017


          Nimble out-of-band authentication for EAP (EAP-NOOB)
                         draft-aura-eap-noob-02

Abstract

   Extensible Authentication Protocol (EAP) provides support for
   multiple authentication methods.  This document defines the EAP-NOOB
   authentication method for nimble out-of-band (OOB) authentication and
   key derivation.  This EAP method is intended for bootstrapping all
   kinds of Internet-of-Things (IoT) devices that have a minimal user
   interface and no pre-configured authentication credentials.  The
   method makes use of a user-assisted one-directional OOB channel
   between the peer device and authentication server.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on November 25, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 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



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   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 Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  EAP-NOOB protocol . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Protocol overview . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Protocol messages and sequences . . . . . . . . . . . . .   8
       3.2.1.  Initial Exchange  . . . . . . . . . . . . . . . . . .   8
       3.2.2.  OOB Step  . . . . . . . . . . . . . . . . . . . . . .  10
       3.2.3.  Completion Exchange . . . . . . . . . . . . . . . . .  12
       3.2.4.  Waiting Exchange  . . . . . . . . . . . . . . . . . .  13
     3.3.  Message data fields . . . . . . . . . . . . . . . . . . .  15
     3.4.  Fast reconnect and rekeying . . . . . . . . . . . . . . .  20
       3.4.1.  Persistent EAP-NOOB association . . . . . . . . . . .  20
       3.4.2.  Reconnect Exchange  . . . . . . . . . . . . . . . . .  21
       3.4.3.  User reset  . . . . . . . . . . . . . . . . . . . . .  23
     3.5.  Key derivation  . . . . . . . . . . . . . . . . . . . . .  24
     3.6.  Error handling  . . . . . . . . . . . . . . . . . . . . .  26
       3.6.1.  Invalid messages  . . . . . . . . . . . . . . . . . .  27
       3.6.2.  Unwanted peer . . . . . . . . . . . . . . . . . . . .  28
       3.6.3.  State mismatch  . . . . . . . . . . . . . . . . . . .  28
       3.6.4.  Negotiation failure . . . . . . . . . . . . . . . . .  28
       3.6.5.  Cryptographic verification failure  . . . . . . . . .  28
       3.6.6.  Application-specific failure  . . . . . . . . . . . .  29
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
     4.1.  Cryptosuites  . . . . . . . . . . . . . . . . . . . . . .  30
     4.2.  Error codes . . . . . . . . . . . . . . . . . . . . . . .  30
     4.3.  Domain name reservation considerations  . . . . . . . . .  31
   5.  Security considerations . . . . . . . . . . . . . . . . . . .  32
     5.1.  Authentication principle  . . . . . . . . . . . . . . . .  32
     5.2.  Identifying and naming peer devices . . . . . . . . . . .  33
     5.3.  Downgrading threats . . . . . . . . . . . . . . . . . . .  35
     5.4.  EAP security claims . . . . . . . . . . . . . . . . . . .  36
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  38
     6.1.  Normative references  . . . . . . . . . . . . . . . . . .  38
     6.2.  Informative references  . . . . . . . . . . . . . . . . .  39
   Appendix A.  Exchanges and events per state . . . . . . . . . . .  40
   Appendix B.  Application-specific parameters  . . . . . . . . . .  41
   Appendix C.  EAP-NOOB Roaming . . . . . . . . . . . . . . . . . .  42
   Appendix D.  OOB message as URL . . . . . . . . . . . . . . . . .  43
   Appendix E.  Example messages . . . . . . . . . . . . . . . . . .  43
   Appendix F.  Version history  . . . . . . . . . . . . . . . . . .  46
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  47



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1.  Introduction

   This document describes a method for registration, authentication and
   key derivation for network-connected ubiquitous computing devices,
   such as consumer and enterprise appliances that are part of the
   Internet of Things (IoT).  These devices may be off-the-shelf
   hardware that is sold and distributed without any prior registration
   or credential-provisioning process.  Thus, the device registration in
   a server database, ownership of the device, and the authentication
   credentials for both network access and application-level security
   must all be established at the time of the device deployment.
   Furthermore, many such devices have only limited user interfaces that
   could be used for their configuration.  Often, the interfaces are
   limited to either only input (e.g. camera) or output (e.g. display
   screen).  The device configuration is made more challenging by the
   fact that the devices may exist in large numbers and may have to be
   deployed or re-configured nimbly based on user needs.

   More specifically, the devices may have the following
   characteristics:

   o  no pre-established relation with a specific server or user,

   o  no pre-provisioned device identifier or authentication
      credentials,

   o  limited user interface and configuration capabilities.

   Many proprietary OOB configuration methods exits for specific IoT
   devices.  The goal of this specification is to provide an open
   standard and a generic protocol for bootstrapping the security of
   network-connected appliances, such as displays, printers, speakers,
   and cameras.  The security bootstrapping in this specification makes
   use of a user-assisted out-of-band (OOB) channel.  The security is
   based on the assumption that attackers are not able to observe or
   modify the messages conveyed through the OOB channel.  We follow the
   common approach of performing a Diffie-Hellman key exchange over the
   insecure network and authenticating the established key with the help
   of the OOB channel in order to prevent man-in-the-middle (MitM)
   attacks.

   The solution presented here is intended for devices that have either
   an input or output interface, such as a camera or display screen,
   which is able to send or receive dynamically generated messages of
   tens of bytes in length.  Naturally, this solution may not be
   appropriate for very small sensors or actuators that have no user
   interface at all.  We also assume that the OOB channel is at least
   partly automated (e.g. camera scanning a bar code) and, thus, there



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   is no need to absolutely minimize the length of the data transferred
   through the OOB channel.  This differs, for example, from Bluetooth
   simple pairing [SimplePairing], where it is critical to minimize the
   length of the manually transferred or compared codes.  Since the OOB
   messages are dynamically generated, we do not support static printed
   registration codes.  This also prevents attacks where a static secret
   code would be leaked.

2.  Terminology

   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 in [RFC2119].

   In addition, this document frequently uses the following terms as
   they have been defined in [RFC5216]:

   authenticator  The entity initiating EAP authentication.

   peer  The entity that responds to the authenticator.  In
         [IEEE-802.1X], this entity is known as the supplicant.

   server  The entity that terminates the EAP authentication method with
         the peer.  In the case where no backend authentication server
         is used, the EAP server is part of the authenticator.  In the
         case where the authenticator operates in pass-through mode, the
         EAP server is located on the backend authentication server.

3.  EAP-NOOB protocol

   This section defines the EAP-NOOB protocol.  The protocol is a
   generalized version of the original idea presented by Sethi et al.
   [Sethi14].

3.1.  Protocol overview

   One EAP-NOOB protocol execution spans multiple EAP exchanges.  This
   is necessary to leave time for the OOB message to be delivered, as
   will be explained below.

   The overall protocol starts with the Initial Exchange, in which the
   server allocates an identifier to the peer, and the server and peer
   negotiate the protocol version and cryptosuite (i.e. cryptographic
   algorithm suite), exchange nonces and perform an Elliptic Curve
   Diffie-Hellman (ECDH) key exchange.  The user-assisted OOB Step then
   takes place.  This step involves only one out-of-band message either
   from the peer to the server or from the server to the peer.  While
   waiting for the OOB Step action, the peer MAY probe the server by



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   reconnecting to it with EAP-NOOB.  If the OOB Step has already taken
   place, the probe leads to the Completion Exchange, which completes
   the mutual authentication and key confirmation.  On the other hand,
   if the OOB Step has not yet taken place, the probe leads to the
   Waiting Exchange, and the peer will perform another probe after a
   server-defined minimum waiting time.  The Initial Exchange and
   Waiting Exchange always end in EAP-Failure, while the Completion
   Exchange may result in EAP-Success.  Once the peer and server have
   performed a successful Completion Exchange, both parties store the
   created association in persistent storage, and the OOB Step is not
   repeated.  Thereafter, creation of new temporal keys, ECDH rekeying,
   and updates of cryptographic algorithms can be achieved with the
   Reconnect Exchange.






































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                                      OOB Output, Initial Exchange,
                                           or Waiting Exchange
                                                  .-----.
                                                  |     v
       .------------------.   Initial       .------------------.
       |                  |   Exchange      |                  |
    .->| 0. Unregistered  |---------------->|1. Waiting for OOB|
    |  |                  |                 |                  |
    |  '------------------'                 '------------------'
    |                                         |      |      ^
   User Reset                 Completion      |      |      |
    |                         Exchange        |     OOB   Initial
    |<-------.      .<------------------------'    Input  Exchange
    |        |      |                                |      |
    |        |      v                                v      |
    |  .------------------.   Completion    .------------------.
    |  |                  |   Exchange      |                  |
    |  |  4. Registered   |<----------------| 2. OOB Received  |
    |  |                  |                 |                  |
    |  '------------------'                 '------------------'
    |        |      ^
    |        |      |
    |  Timeout /   Reconnect
    |   Failure    Exchange
    |        |      |
    |        v      |
    |  .-----------------.
    |  |                 |
    '--| 3. Reconnecting |
       |                 |
       '-----------------'


         Figure 1: EAP-NOOB server-peer association state machine

   Figure 1 shows the association state machine, which is the same for
   the server and for the peer.  When the client initiates the EAP-NOOB
   method, the server chooses the ensuing message exchange based on the
   combination of the server and peer states.  The EAP server and peer
   are initially in the Unregistered state, in which no state
   information needs to be stored.  Before a successful Completion
   Exchange, the server-peer association state is ephemeral in both the
   server and peer (ephemeral states 0..2) , and either party may cause
   the protocol to fall back to the Initial Exchange.  After the
   Completion Exchange has resulted in EAP-Success, the association
   state becomes persistent (persistent states 3..4), and only user
   reset or memory failure can cause the return of the server or the
   peer to the ephemeral states and to the Initial Exchange.



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   The server MUST NOT repeat the OOB Step with the same peer except if
   the association with the peer is explicitly reset by the user or lost
   due to failure of the persistent storage in the server.  In
   particular, once the association has entered the Registered state,
   the server MUST NOT delete the association or go back to states 0-2
   without explicit user approval.  Similarly, the peer MUST NOT repeat
   the OOB Step unless the user explicitly deletes the association with
   the server or resets the peer to the Unregistered state.  The server
   and peer MAY implement user reset of the association by deleting the
   state data from that endpoint.  If they continue to store data about
   the association after the user reset, their behavior SHOULD be
   equivalent to having deleted the association data.

   It can happen that the peer accidentally or through user reset loses
   its persistent state and reconnects to the server without a
   previously allocated peer identifier.  In that case, the server MUST
   treat the peer as a new peer.  The server MAY use auxiliary
   information, such as the PeerInfo field received in the Initial
   Exchange, to detect such multiple association of the same peer.
   However, it MUST NOT delete or merge redundant associations without
   user or application approval because EAP-NOOB internally has no
   secure way of verifying that the two peers are the same physical
   device.  Similarly, the server might lose the association state
   because of a memory failure or user reset.  In that case, the only
   way to recover is that the user resets also the peer.

   A special feature of the EAP-NOOB method is that the server is not
   assumed to have any a-priori knowledge of the peer.  Therefore, the
   peer initially uses the generic identity string "noob@eap-noob.net"
   as the NAI.  The server then allocates a server-specific identifier
   to the peer.  After that, the network access identifier NAI is a
   concatenation of the server-allocated peer identifier and the generic
   suffix "@eap-noob.net".  This suffix serves two purposes: firstly, it
   tells the server that the peer supports and expects the EAP-NOOB
   method and, secondly, it allows routing of the EAP-NOOB sessions to a
   specific authentication server in the AAA architecture.

   EAP-NOOB is an unusual EAP method in that the peer has to connect to
   the server two or more times before it can receive EAP-Success.  The
   reason is that, while EAP allows delays between the request-response
   pairs, e.g. for repeated password entry, the user delays in OOB
   authentication can be much longer than in password trials.  In
   particular, EAP-NOOB supports also peers with no input capability in
   the user interface.  Since these output-only devices cannot be told
   to perform the protocol at the right moment, they have to perform the
   initial exchange opportunistically and hope for the OOB Step to take
   place within a timeout period (NoobTimeout), which is why the timeout
   needs to be several minutes rather than seconds.  For example,



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   consider a printer (peer) from which the OOB message is printed as a
   bar code on paper and then scanned with a camera phone and
   communicated to the server.  To support such devices and slow OOB
   channels, the peer in EAP-NOOB first contacts the server in the
   Initial Exchange, then disconnects for some time, and later continues
   with the Waiting and Completion Exchanges.

3.2.  Protocol messages and sequences

   This section defines the EAP-NOOB exchanges.  The protocol messages
   communicated and the data members in each message are listed in the
   diagrams below.

   Each EAP-NOOB exchange begins with the authenticator sending an EAP-
   Request/Identity packet to the peer.  From this point on, the EAP
   conversation occurs between the server and the peer, and the
   authenticator acts as a pass-through device.  The peer responds to
   the authenticator with an EAP-Response/Identity packet, containing
   the network access identifier (NAI).  The peer MUST compose the NAI
   as defined in Section 3.3.  Essentially, if the peer has no previous
   peer identifier (PeerId), it uses the fixed NAI string "noob@eap-
   noob.net", and if it has received a PeerId from the server, it
   creates the NAI by concatenating the PeerId, a state indicator "+sX",
   and the fixed suffix string "@eap-noob.net".

   After receiving the NAI, the server chooses the EAP-NOOB exchange,
   i.e. the ensuing message sequence, based on the combination of the
   client and server states.  The client recognizes the exchange based
   on the message type field (Type) of the EAP-NOOB request received
   from the server.  The available exchanges are defined in the
   following subsections.  Each exchange comprises one or two EAP
   requests-response pairs and ends in either EAP-Failure, indicating
   that authentication is not (yet) successful, or in EAP-Success.

3.2.1.  Initial Exchange

   Upon receiving the EAP-Response/Identity from the peer, if either the
   peer or the server is in the Unregistered (0) state and the other is
   in one of the ephemeral states (0..2), the server chooses the Initial
   Exchange.

   The Initial Exchange comprises two EAP-NOOB request-response pairs,
   one for version, algorithm and parameter negotiation and the other
   for the ECDH key exchange.  The first EAP-NOOB request (Type=1) from
   the server contains a newly allocated PeerId for the peer and an
   optional Realm.  The server allocates a new PeerId in the Initial
   Exchange regardless of any old PeerId in the username part of the
   received NAI.  The server also sends in the request a list of



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   protocol versions supported (Vers), cryptosuites (Cryptosuites), an
   indicator of the OOB channel directions supported by the server
   (Dirs), and a ServerInfo object.  The peer chooses one of the
   versions and cryptosuites.  The peer sends a response (Type=1) with
   the selected protocol version (Verp), the received PeerId, the
   selected cryptosuite (Cryptosuitep), an indicator of the OOB channel
   directions selected by the peer (Dirp), and a PeerInfo object.  In
   the second EAP-NOOB request and response (Type=2), the server and
   peer exchange the public components of their ECDH keys and nonces
   (PKs,Ns,PKp,Np).  The ECDH keys MUST be based on the negotiated
   cryptosuite.  The Initial Exchange ends with EAP-Failure from the
   server because the authentication cannot yet be completed.

   The server MAY assign a realm to the peer by sending the optional
   Realm field in the Initial Exchange.  In that case, the peer MUST use
   the assigned Realm (together with the allocated PeerId) to construct
   the NAI for the following Waiting, Completion, and Reconnect
   Exchanges with the server.  The peer MUST remember the assigned
   values until a new Initial Exchange or return to Unregistered state.
   Some Authenticators or AAA servers use the assigned Realm to
   determine client-specific connection parameters, such as isolating
   the peer to a specific VLAN.





























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           EAP Peer                                        EAP Server
             |                                                  |
             |<----------- EAP-Request/Identity -|              |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/Identity -------------->|
             |      (NAI=noob|PeerId+sX@eap-noob.net)           |
             |                                                  |
             |                                                  |
             |<----------- EAP-Request/EAP-NOOB ----------------|
             |      (Type=1,Vers,PeerId,[Realm],                |
             |       Cryptosuites,Dirs,ServerInfo)              |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/EAP-NOOB -------------->|
             |      (Type=1,Verp,PeerId,Cryptosuitep,           |
             |        Dirp,PeerInfo)                            |
             |                                                  |
             |                                                  |
             |<----------- EAP-Request/EAP-NOOB ----------------|
             |      (Type=2,PeerId,PKs,Ns,[SleepTime])          |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/EAP-NOOB -------------->|
             |      (Type=2,PeerId,PKp,Np)                      |
             |                                                  |
             |                                                  |
             |<----------- EAP-Failure -------------------------|
             |                                                  |


                        Figure 2: Initial Exchange

   At the conclusion of the Initial Exchange, both the server and the
   peer move to the Waiting for OOB (1) state.

3.2.2.  OOB Step

   The OOB Step, shown as OOB Output and OOB Input in Figure 1, takes
   place after the Initial Exchange.  Depending on the direction
   negotiated, the peer or the server outputs the OOB message containing
   the PeerId, the secret nonce Noob, and the cryptographic fingerprint
   Hoob, as defined in Section 3.3.  This message is then delivered to
   the other party via a user-assisted OOB channel.  The details of the
   OOB channel are defined by the application.

   The receiver of the OOB message MUST compare the received value of
   the fingerprint Hoob with a value that it computes locally, and it



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   MUST reject OOB messages with invalid Hoob.  For usability reasons,
   the receiver SHOULD indicate the acceptance or rejection of the OOB
   message to the user.  The receiver SHOULD reject invalid OOB messages
   without changing its state, until an application-specific number of
   invalid messages (OobRetries) has been reached, after which the
   receiver SHOULD consider it an error and go back to the Unregistered
   (0) state.

   The server or peer MAY send multiple OOB messages with different Noob
   values while in the Waiting for OOB (1) state.  The sender SHOULD
   remember the Noob values until they expire and accept any one of them
   in the following Completion Exchange.  The Noob values sent by the
   server expire after an application-dependent timeout (NoobTimeout),
   and the server MUST NOT accept Noob values older than that in the
   Completion Exchange.  The RECOMMENDED value for NoobTimeout is 3600
   seconds if there are no application-specific reasons for making it
   shorter or longer.  The Noob values sent by the peer expire as
   defined in Section 3.2.4.

   The sender will typically generate a new Noob, and therefore a new
   OOB message, at constant intervals (NoobInterval).  The RECOMMENDED
   interval is NoobInterval = NoobTimeout / 2, so that the two latest
   values are always accepted.  However, the timing of the Noob
   generation may also be based on user interaction or on implementation
   considerations.

   Even though not recommended (see Section 3.3), this specification
   allows both directions to be negotiated (Dirp=3) for the OOB channel.
   In this case, both sides SHOULD output the OOB message, and it is up
   to the user to deliver one of them.


           EAP Peer                                        EAP Server
             |                                                  |
             |=================OOB=============================>|
             |             (PeerId,Noob,Hoob)                   |
             |                                                  |


                Figure 3: OOB Step, from peer to EAP server











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           EAP Peer                                        EAP Server
             |                                                  |
             |<================OOB==============================|
             |             (PeerId,Noob,Hoob)                   |
             |                                                  |


                Figure 4: OOB Step, from EAP server to peer

3.2.3.  Completion Exchange

   After the Initial Exchange, if both the server and the peer support
   the peer-to-server direction for the OOB channel, the peer SHOULD
   initiate the EAP-NOOB method again after an applications-specific
   waiting time in order to probe for completion of the OOB Step.  Also,
   if both sides support the server-to-peer direction of the OOB
   exchange and the peer receives the OOB message, it SHOULD initiate
   the EAP-NOOB method immediately.  Once the server receives the EAP-
   Response/Identity, if one of the server and peer is in the OOB
   Received (2) state and the other is either in the Waiting for OOB (1)
   or OOB Received (2) state, the OOB Step has taken place and the
   server SHOULD continue with the Completion Exchange.

   The Completion Exchange comprises one or two EAP-NOOB request-
   response pairs.  If the peer is in the Waiting for OOB (1) state, the
   OOB message has been sent in the peer-to-server direction.  In that
   case, only one request-response pair (Type=4) takes place.  In the
   request, the server sends the NoobId value, which the peer uses to
   identify the exact OOB message received by the server.  On the other
   hand, if the peer is in the OOB Received (2) state, the direction of
   the OOB message is from server to peer.  In that case, two request-
   response pairs (Type=8 and Type=4) are needed.  With the first
   request, the server discovers NoobId, which identifies the exact OOB
   message received by the peer.  The server returns the same NoobId to
   the peer in the latter request.

   In the last and sometimes only request-response pair (Type=4) of the
   Completion Exchange, the server and peer exchange message
   authentication codes.  Both sides MUST compute the keys Kms and Kmp
   as defined in Section 3.5 and the message authentication codes MACs
   and MACp as defined in Section 3.3.  Both sides MUST compare the
   received message authentication code with a locally computed value.
   If the EAP server finds that it has received the correct value of
   MACp, the Completion Exchange ends in EAP-Success; otherwise, in EAP-
   Failure.

   While it is not expected to occur in practice, poor user interface
   design could lead to two OOB messages delivered simultaneously, one



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   from the peer to the server and the other from the server to the
   peer.  The server detects this event by observing that both the
   server and peer are in the OOB Received state (2).  In that case, the
   server MUST behave as if only the server-to-peer message was
   delivered.

   After successful Completion Exchange, both the server and the peer
   move to the Registered (4) state.  They also derive the output key
   material and store the persistent association state as defined in
   Section 3.4 and Section 3.5.


           EAP Peer                                        EAP Server
             |                                                  |
             |<----------- EAP-Request/Identity -|              |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/Identity -------------->|
             |      (NAI=PeerId+sX@eap-noob.net)                |
             |                                                  |
             |                                                  |
             |<----------- [ EAP-Request/EAP-NOOB ] ------------|
             |      (Type=8,PeerId)                             |
             |                                                  |
             |                                                  |
             |------------ [ EAP-Response/EAP-NOOB ] ---------->|
             |      (Type=8,PeerId,NoobId)                      |
             |                                                  |
             |                                                  |
             |<----------- EAP-Request/EAP-NOOB ----------------|
             |      (Type=4,PeerId,NoobId,MACs)                 |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/EAP-NOOB -------------->|
             |      (Type=4,PeerId,MACp)                        |
             |                                                  |
             |                                                  |
             |<----------- EAP-Success -------------------------|
             |                                                  |


                       Figure 5: Completion Exchange

3.2.4.  Waiting Exchange

   As explained in Section 3.2.3, the peer SHOULD probe the server for
   completion of the OOB Step.  If both the server and client states are
   Waiting for OOB (1), the server will continue with the Waiting



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   Exchange (message Type=3).  The main purpose of this exchange is to
   indicate to the peer that the server has not yet received a peer-to-
   server OOB message.

   In order to limit the rate at which peers probe the server, the
   server MAY send to the peer either in the Initial Exchange or Waiting
   Exchange a minimum time to wait before probing the server again.  A
   peer that has not received an OOB message MUST wait at least the
   server-specified minimum waiting time in seconds (SleepTime) before
   initiating EAP again with the same server.  The peer uses the latest
   SleepTime value that it has received in or after the Initial
   Exchange.  If the server has not sent any SleepTime value, the peer
   SHOULD wait for an application-specified minimum time.

   After the Waiting Exchange, the peer MUST discard Noob values that it
   has sent to the server in OOB messages that are older than the
   application-defined timeout NoobTimeout (see Section 3.2.2).  The
   peer SHOULD discard such expired Noob values even if the probing
   failed, e.g. because of failure to connect to the EAP server or
   incorrect MAC.  The timeout of Noob values is defined like this in
   order to allow the peer to probe the server once after it has waited
   for the server-specified SleepTime.

   If the server and peer have negotiated to use only the server-to-peer
   direction for the OOB channel (Dirp=2), the peer SHOULD nevertheless
   probe the server.  The purpose of this is to keep the server informed
   about the peers that are still waiting for OOB messages.  The server
   MAY set SleepTime to a high number (3600) to prevent the peer from
   probing the server frequently.






















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           EAP Peer                                        EAP Server
             |                                                  |
             |<----------- EAP-Request/Identity -|              |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/Identity -------------->|
             |      (NAI=PeerId+s1@eap-noob.net)                |
             |                                                  |
             |                                                  |
             |<----------- EAP-Request/EAP-NOOB ----------------|
             |      (Type=3,PeerId,[SleepTime])                 |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/EAP-NOOB -------------->|
             |      (Type=3,PeerId)                             |
             |                                                  |
             |                                                  |
             |<----------- EAP-Failure -------------------------|
             |                                                  |


                        Figure 6: Waiting Exchange

3.3.  Message data fields

   Table 1 defines the data fields in the protocol messages.  The in-
   band messages are formatted as JSON objects [RFC7159] in UTF-8
   encoding.  The JSON member names are in the left-hand column of
   table.

   +------------------+------------------------------------------------+
   | Data field       | Description                                    |
   +------------------+------------------------------------------------+
   | Vers,Verp        | EAP-NOOB protocol versions supported by the    |
   |                  | EAP server, and the protocol version chosen by |
   |                  | the peer. Vers is a JSON array of unsigned     |
   |                  | integers, and Verp is an unsigned integer.     |
   |                  | Currently, the only defined values are "[1]"   |
   |                  | and "1", respectively.                         |
   |                  |                                                |
   | PeerId           | Peer identifier. If the peer does not yet have |
   |                  | a peer identifier or it does not remember one, |
   |                  | it uses the NAI "noob@eap-noob.net" in the     |
   |                  | Initial Exchange. The server then assigns an   |
   |                  | identifier to the peer and sends it in the     |
   |                  | first server-to-peer request of the Initial    |
   |                  | Exchange. The assigned identifier is ephemeral |
   |                  | until a successful Completion Exchange takes   |



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   |                  | place. Thereafter, the peer identifier becomes |
   |                  | permanent until the user resets the peer and   |
   |                  | the server. Resetting the server means         |
   |                  | deleting the association for the peer from the |
   |                  | server database. The peer identifier MUST      |
   |                  | follow the syntax of the utf8-username         |
   |                  | specified in [RFC7542]; however, it MUST NOT   |
   |                  | exceed 60 bytes in length and MUST NOT contain |
   |                  | the character '+'. The server MUST generate    |
   |                  | the identifiers in such a way that they do not |
   |                  | repeat and cannot be guessed by the peer or    |
   |                  | third parties beforehand. One way to generate  |
   |                  | the identifiers is to choose a random 16-byte  |
   |                  | identifier and base64url encode it into a      |
   |                  | 22-character string. Another way to generate   |
   |                  | the identifiers is to choose a random          |
   |                  | 22-character alphanumeric string.              |
   |                  |                                                |
   | Realm            | Peer realm. The server may assign a realm to   |
   |                  | the peer. Peer then uses this value as the     |
   |                  | realm part of its NAI. The realm value MUST    |
   |                  | follow the syntax of the uft8-realm specified  |
   |                  | in [RFC7542].                                  |
   |                  |                                                |
   | Peer State "+sX" | This part of the NAI informs the server about  |
   |                  | the peer state. The server uses this           |
   |                  | information together with the server state to  |
   |                  | decide on the type of the exchange and, thus,  |
   |                  | of the type of the next EAP-Request. The peer  |
   |                  | appends the peer state to the PeerId to form   |
   |                  | the username part of the NAI. (Sending it in   |
   |                  | the EAP-Response/Identity message avoids an    |
   |                  | additional round trip for querying the peer    |
   |                  | state.) If the peer is in state 0, it MUST use |
   |                  | the NAI "noob@eap-noob.net"; otherwise, the    |
   |                  | peer MUST create the NAI as the concatenation  |
   |                  | of the PeerId, the string "+s", a single digit |
   |                  | indicating the state of the peer, and the      |
   |                  | string "@eap-noob.net".                        |
   |                  |                                                |
   | Type             | EAP-NOOB message type. The type is an integer  |
   |                  | in the range 0..8. EAP-NOOB requests and the   |
   |                  | corresponding responses share the same type    |
   |                  | value.                                         |
   |                  |                                                |
   | PKs, PKp         | The public components of the ECDH keys of the  |
   |                  | server and peer. PKs and PKp are sent in the   |
   |                  | JSON Web Key (JWK) format [RFC7517].           |



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   |                  |                                                |
   | Cryptosuites,    | The identifiers of cryptosuites supported by   |
   | Cryptosuitep     | the server and of the cryptosuite selected by  |
   |                  | the peer. The format is specified in Section   |
   |                  | 4.1.                                           |
   |                  |                                                |
   | Dirs, Dirp       | OOB channel directions supported by the server |
   |                  | and ones selected by the peer. The possible    |
   |                  | values are 1=peer-to-server, 2=server-to-peer, |
   |                  | 3=both directions. Endpoints that are general- |
   |                  | purpose computers or online services SHOULD    |
   |                  | support both directions. IoT devices with a    |
   |                  | limited user interface will mostly support     |
   |                  | only one direction. If the negotiated value is |
   |                  | 3, the user may be presented with two OOB      |
   |                  | messages, one for each direction, even though  |
   |                  | the user needs to deliver only one of them.    |
   |                  | Since this can be confusing to the user, it is |
   |                  | RECOMMENDED that the peer selects Dirp value 1 |
   |                  | or 2. The EAP-NOOB protocol itself is designed |
   |                  | to cope also with selected value 3, in which   |
   |                  | case it uses the first delivered OOB message.  |
   |                  | In the unlikely case of simultaneously         |
   |                  | delivered OOB messages, the protocol           |
   |                  | prioritizes the server-to-peer direction.      |
   |                  |                                                |
   | Ns, Np           | 32-byte nonces for the Initial Exchange.       |
   |                  |                                                |
   | ServerInfo       | This field contains information about the      |
   |                  | server to be passed from the EAP method to the |
   |                  | application layer in the peer. The information |
   |                  | is specific to the application and it is       |
   |                  | encoded as a JSON object of at most 500 bytes. |
   |                  | It could include, for example, the network     |
   |                  | name and server name or a Uniform Resource     |
   |                  | Locator (URL) [RFC4266] or some other          |
   |                  | information that helps the user to deliver the |
   |                  | OOB message to the server through the out-of-  |
   |                  | band channel.                                  |
   |                  |                                                |
   | PeerInfo         | This field contains information about the peer |
   |                  | to be passed from the EAP method to the        |
   |                  | application layer in the server. The           |
   |                  | information is specific to the application and |
   |                  | it is encoded as a JSON object of at most 500  |
   |                  | bytes. It could include, for example, the peer |
   |                  | make, model and serial number that helps the   |
   |                  | user to distinguish between devices and to     |



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   |                  | deliver the OOB message to the correct peer    |
   |                  | through the out-of-band channel.               |
   |                  |                                                |
   | SleepTime        | The number of seconds for which peer MUST NOT  |
   |                  | start a new execution of the EAP-NOOB method   |
   |                  | with the authenticator, unless the peer        |
   |                  | receives the OOB message or it is reset by the |
   |                  | user. The server can use this field to limit   |
   |                  | the rate at which peers probe it. SleepTime is |
   |                  | an unsigned integer in the range 0..3600.      |
   |                  |                                                |
   | Noob             | 16-byte secret nonce sent through the OOB      |
   |                  | channel and used for the session key           |
   |                  | derivation. The party that received the OOB    |
   |                  | message uses this secret in the Completion     |
   |                  | Exchange to authenticate the exchanged key to  |
   |                  | the party that sent the OOB message.           |
   |                  |                                                |
   | Hoob             | 32-byte cryptographic fingerprint (i.e. hash   |
   |                  | value) computed from all the parameters        |
   |                  | exchanged in the Initial Exchange and in the   |
   |                  | OOB message. Receiving this fingerprint over   |
   |                  | the OOB channel guarantees the integrity of    |
   |                  | the key exchange and parameter negotiation.    |
   |                  | Hence, it authenticates the exchanged key to   |
   |                  | the party that receives the OOB message.       |
   |                  |                                                |
   | NoobId           | 16-byte identifier for the OOB message,        |
   |                  | computed with a one-way function from the      |
   |                  | nonce Noob.                                    |
   |                  |                                                |
   | Ns2, Np2         | 32-byte Nonces for the Reconnect Exchange.     |
   |                  |                                                |
   | MACs, MACp       | Message authentication codes for mutual        |
   |                  | authentication, key confirmation, and          |
   |                  | integrity check on the exchanged information.  |
   |                  | The input to the HMAC is defined below, and    |
   |                  | the key for the HMAC is defined in Section     |
   |                  | 3.5.                                           |
   |                  |                                                |
   | PKs2, PKp2       | The public components of the ECDH keys of the  |
   |                  | server and peer. These MUST be present if a    |
   |                  | new cryptosuite was negotiated. Otherwise,     |
   |                  | either party may omit the field. PKs2 and PKp2 |
   |                  | are sent in the JSON Web Key (JWK) format      |
   |                  | [RFC7517].                                     |
   |                  |                                                |
   | MACs2, MACp2     | Message authentication codes for mutual        |



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   |                  | authentication, key confirmation, and          |
   |                  | integrity check on the Reconnect Exchange. The |
   |                  | input to the HMAC is defined below, and the    |
   |                  | key for the HMAC is defined in Section 3.5.    |
   |                  |                                                |
   +------------------+------------------------------------------------+

                       Table 1: Message data fields

   The nonces in the in-band messages (Ns, Np, Ns2, Np2) are 32-byte
   fresh random byte strings, and the secret nonce Noob is a 16-byte
   fresh random byte string.  All the nonces are generated by the party
   that sends the message.

   The fingerprint Hoob and the identifier NoobId are computed with the
   hash function specified in the negotiated cryptosuite and truncated
   to the 16 leftmost bytes of the output.  The message authentication
   codes (MACs, MACp, MACs2, MACp2) are computed with the HMAC function
   [RFC2104] based on the same cryptographic hash function and truncated
   to the 32 leftmost bytes of the output.

   The inputs to the hash function for computing the fingerprint Hoob
   and to the HMAC for computing MACs, MACp, MACs2 and MACp2 are JSON
   arrays containing a fixed number (16) of members.  The array member
   values MUST be copied to the array verbatim from the in-band
   messages, and space characters or whitespace MUST NOT be added
   anywhere in the JSON structure.

   The inputs for computing the fingerprint and message authentication
   codes are the following:

      Hoob = H(Dir,Vers,Verp,PeerId,Cryptosuites,Dirs,ServerInfo,Cryptos
      uitep,Dirp,[Realm],PeerInfo,PKs,Ns,PKp,Np,Noob).

      NoobId = H("NoobId",Noob).

      MACs = HMAC(Kms; 2,Vers,Verp,PeerId,Cryptosuites,Dirs,ServerInfo,C
      ryptosuitep,Dirp,[Realm],PeerInfo,PKs,Ns,PKp,Np,Noob).

      MACp = HMAC(Kmp; 1,Vers,Verp,PeerId,Cryptosuites,Dirs,ServerInfo,C
      ryptosuitep,Dirp,[Realm],PeerInfo,PKs,Ns,PKp,Np,Noob).

      MACs2 = HMAC(Kms2; 2,Vers,Verp,PeerId,Cryptosuites,"",[ServerInfo]
      ,Cryptosuitep,"",[Realm],[PeerInfo],[PKs2],Ns2,[PKp2],Np2,"")

      MACp2 = HMAC(Kmp2; 1,Vers,Verp,PeerId,Cryptosuites,"",[ServerInfo]
      ,Cryptosuitep,"",[Realm],[PeerInfo],[PKs2],Ns2,[PKp2],Np2,"")




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   Missing input values are represented by empty strings "" in the
   array.  The values indicated with "" are always empty strings.  The
   values in brackets MUST be included if they were exchanged in the
   same Reconnect Exchange; otherwise these values are replaced by empty
   strings "".

   The parameter Dir indicates the direction in which the OOB message
   containing the Noob value is being sent (1=peer-to-server, 2=server-
   to-peer).  This field in needed to prevent the user from accidentally
   delivering the OOB message back to its originator in the rare cases
   where both OOB directions have been negotiated.  The keys for the
   HMACs are defined in the following section.

   The nonces (Ns, Np, Ns2, Np2) and message authentication codes (MACs,
   MACp, MACs2, MACp2) in the in-band messages and in the cryptographic
   function inputs MUST be base64url encoded [RFC4648].  The values Noob
   and Hoob in the OOB channel MAY also be base64url encoded, if that is
   appropriate for the application and the used OOB channel.

   The ServerInfo and PeerInfo are JSON object with UTF-8 encoding.  The
   length of each encoded object as a byte array MUST NOT exceed 500
   bytes.  The format and semantics of these objects MUST be defined by
   the application that uses the EAP-NOOB method.

3.4.  Fast reconnect and rekeying

   EAP-NOOB implements Fast Reconnect ([RFC3748], section 7.2.1) that
   avoids repeated use of the user-assisted OOB channel.

   The rekeying and the Reconnect Exchange may be needed for several
   reasons.  A timeout, software or hardware failure, or user action may
   cause the EAP server, peer or authenticator to lose its non-
   persistent state data such as the EAP output values MSK and EMSK.
   The failure would typically be detected by the peer or authenticator
   when the keys no longer are accepted by the other party.  Change in
   the supported cryptosuites in the EAP server or peer may also cause
   the need for a new key exchange.  When the EAP server or peer detects
   such an event, it MUST change from the Registered to Reconnecting
   state.  These state transitions are labeled Timeout/Failure in
   Figure 1.  The EAP-NOOB method will then perform the Reconnect
   Exchange next time when EAP is triggered.

3.4.1.  Persistent EAP-NOOB association

   To enable rekeying, the EAP server and peer store the session state
   in persistent memory after a successful Completion Exchange.  This
   state data, called "persistent EAP-NOOB association", MUST include at
   least the data fields shown in table Table 2.  They are used for



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   identifying and authenticating the peer in the Reconnect Exchange.
   When a persistent EAP-NOOB association exists, the EAP server and
   peer are in the Registered state (4) or Reconnecting state (3), as
   shown in Figure 1.

   +--------------+---------------------------------+------------------+
   | Data field   | Value                           | Type             |
   +--------------+---------------------------------+------------------+
   | PeerId       | Peer identifier allocated by    | UTF-8 string     |
   |              | server                          | (typically 22    |
   |              |                                 | bytes)           |
   |              |                                 |                  |
   | Realm        | Optional realm assigned by      | UTF-8 string     |
   |              | server (default value is "eap-  |                  |
   |              | noob.net")                      |                  |
   |              |                                 |                  |
   | Cryptosuitep | Negotiated cryptosuite          | integer          |
   |              |                                 |                  |
   | Kz           | Persistent key material         | 32 bytes         |
   +--------------+---------------------------------+------------------+

                 Table 2: Persistent EAP-NOOB association

3.4.2.  Reconnect Exchange

   The server chooses the Reconnect Exchange when peer is in the
   Reconnecting (3) state and the server itself is in the Registered (4)
   or Reconnecting (3) state.  The peer MUST NOT initiate EAP-NOOB when
   the peer is in Registered state.

   The Reconnect Exchange comprises three EAP-NOOB request-response
   pairs, one for algorithm and parameter negotiation, another for the
   nonce and key exchange, and the last one for exchanging message
   authentication codes.  In the first request and response (Type=5) the
   server and peer negotiate a cryptosuite in the same way as in the
   Initial Exchange.  The messages MAY also contain PeerInfo and
   ServerInfo objects.  In the second request and response (Type=6), the
   server and peer exchange the public components of ECDH keys and the
   nonces (PKs2,Ns2,PKp2,Np2).  The server ECDH key MUST be fresh, i.e.
   not previously used with the same peer, and the client ECDH key
   SHOULD be fresh, i.e. not previously used.  In the third and final
   request and response (Type=7), the server and peer exchange the
   message authentication codes (MACs2,MACp2).  Both sides MUST compute
   the keys Kms2 and Kmp2 as defined in Section 3.5 and the message
   authentication codes MACs2 and MACp2 as defined in Section 3.3.  Both
   sides MUST compare the received message authentication code with a
   locally computed value.  If the EAP server finds that it has received




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   the correct value of MACp, the Completion Exchange ends in EAP-
   Success; otherwise, in EAP-Failure.

   If the negotiated cryptosuite is the same as previously, the server
   MAY refuse to perform a new ECDH exchange by omitting PKs2, and the
   peer MAY refuse by omitting PKp2.  If the server omits PKs2, the peer
   SHOULD also omit PKp2.  When one or both public keys are not present,
   the new EAP output values are derived from the fresh nonces and the
   previously established shared key Kz, as defined in Section 3.5.  The
   security property lost by refusing the ECDH exchange is forward
   secrecy.

   The server and client MAY send updated Realm, ServerInfo and PeerInfo
   objects in the Reconnect Exchange.  If there is no update to the
   values, they SHOULD omit this information from the messages.

   Both sides MUST compare the received message authentication code with
   a locally computed value.  If the EAP server finds that it has
   received the correct value of MACp2, the Reconnect Exchange ends in
   EAP-Success; otherwise, in EAP-Failure.

   After successful Reconnect Exchange, both the server and the peer
   move to the Registered (4) state.  If the Realm was updated or if a
   new cryptosuite and Kz were negotiated, they also update the
   persistent EAP-NOOB association with the changed values.


























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           EAP Peer                                        EAP Server
             |                                                  |
             |<----------- EAP-Request/Identity -|              |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/Identity -------------->|
             |      (NAI=PeerId+s3@eap-noob.net)                |
             |                                                  |
             |                                                  |
             |<----------- EAP-Request/EAP-NOOB ----------------|
             |      (Type=5,PeerId,Cryptosuites,                |
             |       [Realm],[ServerInfo])                      |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/EAP-NOOB -------------->|
             |      (Type=5,PeerId,Cryptosuitep,[PeerInfo])     |
             |                                                  |
             |                                                  |
             |<----------- EAP-Request/EAP-NOOB ----------------|
             |      (Type=6,PeerId,[PKs2,]Ns2)                  |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/EAP-NOOB -------------->|
             |      (Type=6,PeerId,[PKp2,]Np2)                  |
             |                                                  |
             |                                                  |
             |<----------- EAP-Request/EAP-NOOB ----------------|
             |      (Type=7,PeerId,MACs2)                       |
             |                                                  |
             |                                                  |
             |------------ EAP-Response/EAP-NOOB -------------->|
             |      (Type=7,PeerId,MACp2)                       |
             |                                                  |
             |                                                  |
             |<----------- EAP-Success -------------------------|
             |                                                  |


                       Figure 7: Reconnect Exchange

3.4.3.  User reset

   As shown in the association state machine in Figure 1, the only
   specified way for the association to return from the Registered state
   (4) to the Unregistered state (0) is through user-initiated reset.
   After the reset, a new OOB message will be needed to establish a new
   association between the EAP server and peer.  Typical situations in
   which the user reset is required are when the other side has



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   accidentally lost the persistent EAP-NOOB association data, or when
   the peer device is decommissioned.

   The server could detect that the peer is in the Registered or
   Reconnecting state but the server itself is in one of the ephemeral
   states 0..2 (including situations where the server does not recognize
   the PeerId).  In this case, effort should be made to recover the
   persistent server state, for example, from a backup storage -
   especially if many peer devices are similarly affected.  If that is
   not possible, the EAP server SHOULD log the error or notify an
   administrator.  The only way to continue from such a situation is by
   having the user reset the peer device.

   On the other hand, if the peer is in any of the ephemeral states
   0..2, including the Unregistered state, the server will treat the
   peer as a new peer device and allocate a new PeerId to it.  The
   PeerInfo can be used by the administrator as a clue to which physical
   device has lost its state.  However, there is no secure way of
   matching the "new" peer with the old PeerId without repeating the OOB
   Step.  This situation will be resolved when the user performs the OOB
   Step and, thus, identifies the physical peer device.  The server user
   interface SHOULD support situations where the "new" peer is actually
   a previously registered peer that has been reset by a user or has
   otherwise lost the persistent EAP-NOOB association data and needs to
   be merged with the old peer data in the server.

3.5.  Key derivation

   EAP-NOOB derives the EAP output values MSK and EMSK and other secret
   keying material from the output of an Elliptic Curve Diffie-Hellman
   (ECDH) algorithm following the NIST specification [NIST-DH].  In NIST
   terminology, we use a C(2, 0, ECC CDH) scheme, i.e. two ephemeral
   keys and no static keys.  In the Initial and Rekeying Exchange, the
   server and peer compute the ECDH shared secret Z as defined in
   section 6.1.2.2 of the NIST specification.  In the Completion and
   Rekeying Exchange, the server and peer compute the secret keying
   material from Z with the single-step key derivation function (KDF)
   defined in section 5.8.1 of the NIST specification.  The hash
   function H for KDF is taken from the negotiated cryptosuite.

   Table 3 defines the inputs to the KDF.  In the Completion Exchange,
   the input Z comes from the preceding Initial exchange, while the
   Rekeying Exchange uses the Z just created.  The KDF takes some
   additional inputs (OtherInfo), for which we use the concatenation
   format defined in section 5.8.1.2.1 of the NIST specification.
   OtherInfo consists of the AlgorithmId, PartyUInfo, PartyVInfo, and
   SuppPrivInfo fields.  The three first ahve fixed length, and
   SuppPrivInfo have fixed length, and SuppPrivInfo has a one-byte



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   Datalength.  AlgorithmId is the fixed-length 8-byte ASCII string
   "EAP-NOOB".  The other input values are the server's and peer's
   nonces.  In the Completion Exchange, the inputs also include the
   secret nonce Noob from the OOB message, while in the Rekeying
   Exchange, it is replaced by the shared secret Kz from the persistent
   EAP-NOOB association.

   A special case of the rekeying occurs if no ECDH public keys were
   exchanged in the Reconnect Exchange (or if only one party sent its
   public key).  In this case, input Z to the KDF is replaced with the
   shared key Kz from the persistent EAP-NOOB association.  The result
   is rekeying without the computational cost of the ECDH exchange, but
   also without forward secrecy.

   +---------------+--------------+-----------------------+------------+
   | Exchange      | KDF input    | Value                 | Length     |
   |               | field        |                       | (bytes)    |
   +---------------+--------------+-----------------------+------------+
   | Completion    | Z            | ECDH shared secret    | variable   |
   |               |              | from PKs and PKp      |            |
   |               | AlgorithmId  | "EAP-NOOB"            | 8          |
   |               | PartyUInfo   | Np                    | 32         |
   |               | PartyVInfo   | Ns                    | 32         |
   |               | SuppPubInfo  | (not allowed)         |            |
   |               | SuppPrivInfo | Noob                  | 16         |
   |               |              |                       |            |
   | Rekeying with | Z            | ECDH shared secret    | variable   |
   | ECDH          |              | from PKs2 and PKp2    |            |
   |               | AlgorithmId  | "EAP-NOOB"            |            |
   |               | PartyUInfo   | Np2                   | 32         |
   |               | PartyVInfo   | Ns2                   | 32         |
   |               | SuppPubInfo  | (not allowed)         |            |
   |               | SuppPrivInfo | Kz                    | 32         |
   |               |              |                       |            |
   | Rekeying      | Z            | Kz                    | 32         |
   | without ECDH  | AlgorithmId  | "EAP-NOOB"            |            |
   |               | PartyUInfo   | Np2                   | 32         |
   |               | PartyVInfo   | Ns2                   | 32         |
   |               | SuppPubInfo  | (not allowed)         |            |
   |               | SuppPrivInfo | (null)                | 0          |
   +---------------+--------------+-----------------------+------------+

                       Table 3: Key derivation input

   Table 3 defines how the output bytes of the KDF are used.  In
   addition to the EAP output values MSK and EMSK, the server and peer
   derive another shared secret key AMSK, which MAY be used for
   application-layer security.  Further output bytes are used internally



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   by EAP-NOOB for the message authentication keys (Kms,Kmp,Kms2,Kmp2).
   The Completion Exchange also produces the shared secret Kz, which the
   server and peer store in the persistent EAP-NOOB association.  The
   Rekeying Exchange updates Kz only when a new cryptosuite is
   negotiated.  In that case, the server and peer update both the
   cryptosuite and Kz in the persistent EAP-NOOB association.

   +---------------------+------------------+---------+----------------+
   | Exchange            | KDF output bytes | Used as | Length (bytes) |
   +---------------------+------------------+---------+----------------+
   | Completion          | 0..63            | MSK     | 64             |
   |                     | 64..127          | EMSK    | 64             |
   |                     | 128..191         | AMSK    | 64             |
   |                     | 192..223         | Kms     | 32             |
   |                     | 224..255         | Kmp     | 32             |
   |                     | 256..287         | Kz      | 32             |
   |                     |                  |         |                |
   | Rekeying, no change | 0..63            | MSK     | 64             |
   | in cryptosuite      | 64..127          | EMSK    | 64             |
   |                     | 128..191         | AMSK    | 64             |
   |                     | 192..223         | Kms2    | 32             |
   |                     | 224..255         | Kmp2    | 32             |
   |                     |                  |         |                |
   | Rekeying, new       | 0..63            | MSK     | 64             |
   | cryptosuite         | 64..127          | EMSK    | 64             |
   | negotiated          | 128..191         | AMSK    | 64             |
   |                     | 192..223         | Kms2    | 32             |
   |                     | 224..255         | Kmp2    | 32             |
   |                     | 256..287         | Kz      | 32             |
   |                     |                  |         |                |
   +---------------------+------------------+---------+----------------+

                      Table 4: Key derivation output

3.6.  Error handling

   Various error conditions in EAP-NOOB are handled by sending an error
   notification message (type=0) instead of the expected next EAP
   request or response message.  Both the EAP server and the peer may
   send the error notification, as shown in Figure 8 and Figure 9.
   After sending or receiving an error notification, the server MUST
   send an EAP-Failure message.  The notification MAY contain an
   ErrorInfo field, which is a UTF-8 encoded text string with a maximum
   length of 500 bytes.  It is used for sending descriptive information
   about the error for logging and debugging purposes.






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           EAP Peer                                        EAP Server
            ...                                                ...
             |                                                  |
             |<----------- EAP-Request/EAP-NOOB ----------------|
             |        (Type=0,[PeerId],ErrorCode,[ErrorInfo])   |
             |                                                  |
             |                                                  |
             |<----------- EAP-Failure -------------------------|
             |                                                  |


             Figure 8: Error notification from server to peer


           EAP Peer                                        EAP Server
            ...                                                ...
             |                                                  |
             |------------ EAP-Response/EAP-NOOB -------------->|
             |        (Type=0,[PeerId],ErrorCode,[ErrorInfo])   |
             |                                                  |
             |                                                  |
             |<----------- EAP-Failure -------------------------|
             |                                                  |


             Figure 9: Error notification from peer to server

   After an error notification, the server and peer set their state as
   follows.  In the Initial Exchange, both the sender and recipient of
   the error notification MUST set the association state to the
   Unregistered (0) state.  In the Waiting and Completion Exchanges,
   each side MUST remain in its old state as if the failed exchange did
   not take place, with the exception that the peer checks for expiry of
   the Noob value as defined in Section 3.2.4.  In the Reconnect
   Exchange, both sides MUST set the association state to the
   Reconnecting (3) state.

   Errors that occur in the OOB channel are not explicitly notified in-
   band.

3.6.1.  Invalid messages

   If the NAI structure is invalid, the server SHOULD send the error
   code 1001 to the peer.  The recipient of an EAP-NOOB request or
   response SHOULD send the following error codes back to the sender:
   1002 if it cannot parse the message as a JSON object or the top-level
   JSON object has missing or unrecognized members; 1003 if a data field
   has an invalid value, such as an integer out of range; 1004 if the



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   received message type was unexpected; 1005 if the PeerId has an
   unexpected value; 1006 if the NoobId is not recognized; and 1007 if
   the ECDH key is invalid.

3.6.2.  Unwanted peer

   The preferred way for the EAP server to rate limit EAP-NOOB
   connections from a peer is to use the SleepTime parameter in the
   Waiting Exchange.  However, if the EAP server receives repeated EAP-
   NOOB connections from a peer which is apparently should not connect
   to this server, the server MAY indicate that the connections are
   unwanted by sending the error code 2001.  After receiving this error
   message, the peer MAY refrain from reconnecting to the same EAP
   server and, if possible, both the EAP server and peer SHOULD indicate
   this error condition to the user.  However, in order to avoid
   persistent denial of service, the peer is not required to stop
   entirely from reconnecting to the server.

3.6.3.  State mismatch

   In the states indicated by "-" in Figure 10 in Appendix A, user
   action is required to reset the association state or to recover it,
   for example, from backup storage.  In those cases, the server sends
   the error code 2002 to the peer.  If possible, both the EAP server
   and peer SHOULD indicate this error condition to the user.

3.6.4.  Negotiation failure

   If there is no matching protocol version, the peer sends the error
   code 3001 to the server.  If there is no matching cryptosuite, the
   peer sends the error code 3002 to the server.  If there is no
   matching OOB direction, the peer sends the error code 3003 to the
   server.

   In practice, there is no way of recovering from these errors without
   software or hardware changes.  If possible, both the EAP server and
   peer SHOULD indicate these error conditions to the user.  In
   particular, user action is needed for changing the association from a
   persistent state to the Unregistered (0) state.

3.6.5.  Cryptographic verification failure

   If the recipient of the OOB message detects an unrecognized PeerId or
   incorrect fingerprint (Hoob) in the OOB message, the recipient MUST
   remain in the Waiting for OOB state (1) as if no OOB message was
   received.  The recipient SHOULD indicate the failure to accept the
   OOB message to the user.




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   Note that if the OOB message was delivered from the server to the
   peer and the peer does not recognize the PeerId, the likely cause is
   that the user has unintentionally delivered the OOB message to the
   wrong destination.  If possible, the peer SHOULD indicate this to the
   user; however, the peer device may not have capability for many
   different error indications and it MAY use the same method or error
   indication as in the case of an incorrect fingerprint.

   The rationale for the above is that the invalid OOB message could
   have been presented to the recipient by mistake or intentionally by a
   malicious party and, thus, it should be ignored in the hope that the
   honest user will soon deliver a correct OOB message.

   If the EAP server or peer detects an incorrect message authentication
   code (MACs, MACp, MACs2, MACp2), it sends the error code 4001 to the
   other side.  As specified in the beginning of Section 3.6, the failed
   Completion Exchange will not result in server or peer state changes
   while error in the Reconnect Exchange will put both sides to the
   Reconnecting (3) state and thus lead to another reconnect attempt.

   The rationale for this is that the invalid cryptographic message may
   have been spoofed by a malicious party and, thus, it should be
   ignored.  In particular, a spoofed message on the in-band channel
   should not force the honest user to perform the OOB Step again.  In
   practice, however, the error may be caused by other failures, such as
   software bug.  For this reason, the EAP server MAY limit the rate of
   peer connections with SleepTime after the above error.  Also, there
   MUST be a way for the user to reset the EAP server and peer to the
   Unregistered state (0), so that the OOB Step can be repeated.

3.6.6.  Application-specific failure

   Applications MAY define new error messages for failures that are
   specific to the application or to one type of OOB channel.  They MAY
   also use the generic application-specific error code 5001, or the
   error codes 5002 and 5003, which have been reserved for indicating
   invalid data in the ServerInfo and PeerInfo fields, respectively.
   Additionally, anticipating OOB channels that make use of a URL, the
   error code 5003 have been reserved for indicating invalid server URL.

4.  IANA Considerations

   This section provides guidance to the Internet Assigned Numbers
   Authority (IANA) regarding registration of values related to the EAP-
   NOOB protocol, in accordance with [RFC5226].

   The EAP Method Type number for EAP-NOOB needs to be assigned.




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   This memo also requires IANA to create new registries as defined in
   the following subsections.

4.1.  Cryptosuites

   An EAP server MUST supply one or more suggestions for cryptosuites as
   the Cryptosuites value in the Initial Exchange.  They are formatted
   as a JSON array of the identifier integers.  Each suite MUST appear
   only once in the array.  The cryptosuites MUST be supplied in the
   order of priority.  Peers MUST supply exactly one suite in the
   Cryptosuitep value, formatted as an identifier integer.  The
   following suites are defined by EAP-NOOB:

         +-------------+-----------------------------------------+
         | Cryptosuite | Algorithms                              |
         +-------------+-----------------------------------------+
         | 1           | Curve25519 [RFC7748], SHA-256 [RFC6234] |
         +-------------+-----------------------------------------+

                      Table 5: EAP-NOOB cryptosuites

   Assignment of new values for new cryptosuites MUST be done through
   IANA with "Specification Required" and "IESG Approval" as defined in
   [RFC5226].

4.2.  Error codes

   The error codes defined by EAP-NOOB are listed in Table 6.























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          +------------+----------------------------------------+
          | Error code | Purpose                                |
          +------------+----------------------------------------+
          | 1001       | Invalid NAI or peer state              |
          | 1002       | Invalid message structure              |
          | 1003       | Invalid data                           |
          | 1004       | Unexpected message type                |
          | 1005       | Unexpected peer identifier             |
          | 1006       | Unrecognized OOB message identifier    |
          | 1007       | Invalid ECDH key                       |
          | 2001       | Unwanted peer                          |
          | 2002       | State mismatch, user action required   |
          | 3001       | No mutually supported protocol version |
          | 3002       | No mutually supported cryptosuite      |
          | 3003       | No mutually supported OOB direction    |
          | 4001       | MAC verification failure               |
          | 5001       | Application-specific error             |
          | 5002       | Invalid server info                    |
          | 5003       | Invalid server URL                     |
          | 5004       | Invalid peer info                      |
          +------------+----------------------------------------+

                       Table 6: EAP-NOOB error codes

   Assignment of new error codes MUST be done through IANA with
   "Specification Required" and "IESG Approval" as defined in [RFC5226].

4.3.  Domain name reservation considerations

   "eap-noob.net" should be registered as a special-use domain.  The
   considerations required by [RFC6761] for registering this special use
   domain name are as follows:

   o  Users: Non-admin users are not expected to encounter this name or
      recognize it as special.  AAA administrators may need to recognize
      the name.

   o  Application Software: Application software is not expected to
      recognize this domain name as special.

   o  Name Resolution APIs and Libraries: Name resolution APIs and
      libraries are not expected to recognize this domain name as
      special.

   o  Caching DNS Servers: Caching servers are not expected to recognize
      this domain name as special.





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   o  Authoritative DNS Servers: Authoritative DNS servers MUST respond
      to queries for eap-noob.net with NXDOMAIN.

   o  DNS Server Operators: Except for the authoritative DNS server,
      there are no special requirements for the operators.

   o  DNS Registries/Registrars: There are no special requirements for
      DNS registrars.

5.  Security considerations

   EAP-NOOB is an authentication and key derivation protocol and, thus,
   security considerations can be found in most sections of this
   specification.  In the following, we explain the protocol design and
   highlight some other special considerations.

5.1.  Authentication principle

   The mutual authentication in EAP-NOOB is based on two separate
   features, both conveyed in the OOB message.  The first authentication
   feature is the secret nonce Noob.  The peer and server use this
   secret in the Completion Exchange to mutually authenticate the
   session key previously created with ECDH.  The message authentication
   codes computed with the secret nonce Noob are alone sufficient for
   authenticating the key exchange.  The OOB channel might, however, be
   vulnerable to eavesdropping of the OOB channel, which could lead to
   compromise of the secret nonce, which will then enable a man-in-the-
   middle attack on the in-band channel.  This is why we include, as a
   second authentication feature, the integrity-protecting fingerprint
   Hoob in the OOB message.  It is typically more difficult to spoof or
   alter messages on the human-assisted OOB channel, such as bar code,
   sound burst or user-transferred URL, than it is to spy on them.

   The security provided by the cryptographic fingerprint is somewhat
   intricate to understand.  The party that receives the OOB message
   uses Hoob to verify the integrity of the ECDH exchange.  Thus, that
   party can detect man-in-the-middle attacks on the in-band channel.
   The other party, however, is not equally protected because the OOB
   message and fingerprint are sent only in one direction.  Some
   protection to the OOB sender is afforded by the fact that the user
   may notice the failure of the association at the OOB receiver and
   therefore reset the OOB sender.  Indeed, other device-pairing
   protocols have solved a similar situation by requiring the user to
   confirm to the OOB sender that the association was accepted by the
   OOB-receiver, e.g. by pressing an "accept" button on the sender.
   Since EAP-NOOB was designed to work strictly with one-directional OOB
   communication, it does not rely on such input to the OOB sender.




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   To summarize, EAP-NOOB uses the combined protection of the secret
   nonce Noob and the cryptographic fingerprint Hoob, both conveyed in
   the OOB message.  The secret nonce Noob alone is sufficient for
   mutual authentication, unless the attacker can eavesdrop it from the
   OOB channel.  If an attacker is able to eavesdrop the secret nonce
   and performs a man-in-the-middle attack on the in-band channel, the
   mismatching fingerprint will alert the OOB receiver, which will
   reject the OOB message.  In this case, the association will appear to
   be complete only on the OOB sender side.  The user in many
   applications will detect this apparently one-sided association
   because the peer device does not appear registered on the server or
   network.

   The expected use cases for EAP-NOOB are ones where it replaces a
   user-entered access credentials.  In wireless network access for IoT
   devices, the user-entered credential is often a passphrase, which is
   shared by all the network stations.  Like any other EAP-based
   solution, EAP-NOOB establishes a different master secret for each
   peer device, which is obviously more resilient to device compromise
   than a common master secret.  Additionally, it is possible to revoke
   the security association for an individual device on the server side.

   Forward secrecy in EAP-NOOB is optional.  The Reconnect Exchange in
   EAP-NOOB provides forward secrecy only if both the server and peer
   send their fresh ECDH keys.  This allows both the server and the peer
   to limit the frequency of the costly computation that is required for
   forward secrecy.  The server should make its decision primarily based
   on what it knows about the peer's computational capabilities.

5.2.  Identifying and naming peer devices

   EAP-NOOB relies on physical possession or identification of the peer
   device and secure communication between the user and the server.  The
   main remaining threat against EAP-NOOB is that the attacker performs
   a man-in-the-middle attack on the in-band channel and, during the
   protocol execution, tricks the user to deliver the OOB message to or
   from the wrong peer.  The server will now be associated with that
   wrong peer.  Similarly, the attacker could try to trick the user to
   accessing the wrong server in the OOB Step.  This reliance on user in
   identifying the correct parties is an inherent property of out-of-
   band authentication.

   One mechanism that can be used to mitigate user mistakes is
   certification of trusted servers and peer devices.  For example, if
   used together with EAP-NOOB, vendor certificates could prevent
   accidental association with a rogue peer device.  Compared to a fully
   certificate-based authentication, EAP-NOOB does not depend on trusted




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   third parties and does not require the user to know the identifier of
   the peer device; physical access is sufficient.

   The user could also accidentally deliver the OOB message to more than
   one peer device.  This could, for example, occur if the OOB message
   is a bar code and the peer is a camera: the user could by mistake
   show the bar code first to the wrong camera.  Such accidents in EAP-
   NOOB will not enable the wrong camera to compute the master key or to
   opportunistically eavesdrop the communication.  This is because the
   wrong peer device would need to have performed a man-in-the middle
   attack on the in-band channel before the accident.  In comparison,
   simpler solutions where the master key is transferred to the device
   via the OOB channel would be vulnerable to opportunistic attacks if
   the user mistakenly delivers the master key to more than one device.

   The PeerId value in the protocol is a server-allocated identifier for
   its association with the peer and SHOULD NOT be shown to the user
   because its value is initially ephemeral.  Since the PeerId is
   allocated by the server and the scope of the identifier is the single
   server, the so-called identifier squatting attacks, where a malicious
   peer could reserve another peer's identifier, are not possible in
   EAP-NOOB.  The server SHOULD assign a random or pseudo-random PeerId
   to each new peer.  It SHOULD NOT select the PeerId based on any peer
   characteristics that it may know, such as the peer's link-layer
   network address.

   User reset or failure in the OOB step can cause the peer to perform
   many Initial Exchanges with the server and to allocate many PeerIds
   and to store the ephemeral protocol state for them.  The peer will
   typically only remember the latest one.  EAP-NOOB leaves it to the
   implementation to decide when to delete these ephemeral associations.
   There is no security reason to delete them early, and the server does
   not have any way to verify that the peers are actually the same one.
   Thus, it is safest to store the ephemeral states for at least one
   day.  If the OOB messages are sent only in the server-to-peer
   direction, the server SHOULD NOT delete the ephemeral state before
   all the related Noob values have expired.

   After completion of EAP-NOOB, the server may store the PeerInfo data,
   and the user may use it to identify the peer and its properties, such
   as make and model or serial number.  A compromised peer could lie
   about this information in the PeerInfo that it sends to the server.
   If the server stores any information about the peer, it is important
   that this information is approved by the user during or after the OOB
   Step.  Without rigorous user checking, the PeerInfo is not
   authenticated information and should not be relied on.  Therefore, it
   is better to include only minimal information about the peer in
   PeerInfo and to ask the user to name the peer devices.  In many



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   applications, such as OOB authentication for ad-hoc wireless network
   access, it may be unnecessary to store any names for the peer device.
   Since the user delivering the OOB message will often communicate with
   the server over an authenticated channel, e.g. by logging into a
   secure web page, the user identity and user-given name can in those
   cases be reliably stored for the peer device.  It is these user
   identities and user-given names that should be later used for access
   control and revocation.

   Another reason to include only minimal information in the PeerInfo is
   potential privacy issues.  The PeerInfo field is typically
   transmitted in plaintext between the peer and the authenticator.
   Although the PeerInfo sent by a new, unregistered device will not
   leak any information specifically about the user, it could reveal
   device identifiers and information about other device properties,
   which the user may want to avoid leaking at this point.

5.3.  Downgrading threats

   The fingerprint Hoob protects all the information exchanged in the
   Initial Exchange, including the cryptosuite negotiation.  The message
   authentication codes MACs and MACp also protect the same information.
   The message authentication codes MACs2 and MACp2 protect information
   exchanged during key renegotiation in the Reconnect Exchange.  This
   prevents downgrade attacks to weaker cryptosuites as long as the
   possible attacks take more time than the maximum time allowed for the
   EAP-NOOB completion.  This is typically the case for recently
   discovered cryptanalytic attacks.

   As an additional precaution, the EAP server and peer SHOULD check for
   downgrading attacks in the Reconnect Exchange.  As long as the server
   or peer saves any information about the other party, it SHOULD also
   remember the previously negotiated cryptosuite and not accept
   renegotiation of any cryptosuite that is known to be weaker than the
   previous one (e.g. a deprecated cryptosuite or the same ECDH field
   with a shorter key).

   Integrity of the direction negotiation cannot be verified in the same
   way as the integrity of the cryptosuite negotiation.  That is, if the
   OOB channel used in an application is critically insecure in one
   direction, a man-in-the-middle attacker could modify the negotiation
   messages and thereby cause that direction to be used.  Applications
   that support OOB messages in both directions SHOULD therefore ensure
   that the OOB channel has sufficiently strong security in both
   directions.  While this is a theoretical vulnerability, it could
   arise in practice if EAP-NOOB is deployed in unexpected applications.
   However, most devices acting as the peer are likely to support only
   one direction of exchange, in which case interfering with the



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   direction negotiation can only prevent the completion of the
   protocol.

   The long-term shared key material Kz in the persistent EAP-NOOB
   association is established with an ECDH key exchange when the peer
   and server are first associated.  It is a weaker secret than a
   manually configured random shared key because advances in
   cryptanalysis against the used ECDH curve could eventually enable the
   attacker to recover Kz.  EAP-NOOB protect against such attacks by
   allowing cryptosuite upgrade in the Reconnect Exchange.  We do not
   expect the upgrades to be frequent, but if one becomes necessary, the
   upgrade can be made without manual resetting and reassociation of the
   peer devices.  During the algorithm upgrade, the shared key material
   Kz is also updated.

5.4.  EAP security claims

   EAP security claims are defined in section 7.2.1 of [RFC3748].  The
   security claims for EAP-NOOB are listed in Table 7.
































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   +----------------+--------------------------------------------------+
   | Security       | EAP-NOOB claim                                   |
   | property       |                                                  |
   +----------------+--------------------------------------------------+
   | Authentication | ECDH key exchange with out-of-band               |
   | mechanism      | authentication                                   |
   |                |                                                  |
   | Protected      | yes                                              |
   | cryptosuite    |                                                  |
   | negotiation    |                                                  |
   |                |                                                  |
   | Mutual         | yes                                              |
   | authentication |                                                  |
   |                |                                                  |
   | Integrity      | yes                                              |
   | protection     |                                                  |
   |                |                                                  |
   | Replay         | yes                                              |
   | protection     |                                                  |
   |                |                                                  |
   | Key derivation | yes                                              |
   |                |                                                  |
   | Key strength   | The specified cryptosuites provide key strength  |
   |                | of at least 128 bits.                            |
   |                |                                                  |
   | Dictionary     | yes                                              |
   | attack         |                                                  |
   | protection     |                                                  |
   |                |                                                  |
   | Fast reconnect | yes                                              |
   |                |                                                  |
   | Cryptographic  | not applicable                                   |
   | binding        |                                                  |
   |                |                                                  |
   | Session        | yes                                              |
   | independence   |                                                  |
   |                |                                                  |
   | Fragmentation  | no                                               |
   |                |                                                  |
   | Channel        | yes (The ServerInfo and PeerInfo can be used to  |
   | binding        | convey integrity-protected channel properties    |
   |                | such as peer MAC address.)                       |
   +----------------+--------------------------------------------------+

                       Table 7: EAP security claims






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6.  References

6.1.  Normative references

   [NIST-DH]  Barker, E., Chen, L., Roginsky, A., and M. Smid,
              "Recommendation for Pair-Wise Key Establishment Schemes
              Using Discrete Logarithm Cryptography", NIST Special
              Publication 800-56A Revision 2 , May 2013,
              <http://nvlpubs.nist.gov/nistpubs/SpecialPublications/
              NIST.SP.800-56Ar2.pdf>.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,
              <http://www.rfc-editor.org/info/rfc2104>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, Ed., "Extensible Authentication Protocol
              (EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
              <http://www.rfc-editor.org/info/rfc3748>.

   [RFC4266]  Hoffman, P., "The gopher URI Scheme", RFC 4266,
              DOI 10.17487/RFC4266, November 2005,
              <http://www.rfc-editor.org/info/rfc4266>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <http://www.rfc-editor.org/info/rfc4648>.

   [RFC5216]  Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
              Authentication Protocol", RFC 5216, DOI 10.17487/RFC5216,
              March 2008, <http://www.rfc-editor.org/info/rfc5216>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,
              <http://www.rfc-editor.org/info/rfc6234>.




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   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,
              <http://www.rfc-editor.org/info/rfc6761>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <http://www.rfc-editor.org/info/rfc7159>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <http://www.rfc-editor.org/info/rfc7517>.

   [RFC7542]  DeKok, A., "The Network Access Identifier", RFC 7542,
              DOI 10.17487/RFC7542, May 2015,
              <http://www.rfc-editor.org/info/rfc7542>.

   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
              for Security", RFC 7748, DOI 10.17487/RFC7748, January
              2016, <http://www.rfc-editor.org/info/rfc7748>.

6.2.  Informative references

   [IEEE-802.1X]
              Institute of Electrical and Electronics Engineers, "Local
              and Metropolitan Area Networks: Port-Based Network Access
              Control", IEEE Standard 802.1X-2004. , December 2004.

   [RFC2904]  Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L.,
              Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and
              D. Spence, "AAA Authorization Framework", RFC 2904,
              DOI 10.17487/RFC2904, August 2000,
              <http://www.rfc-editor.org/info/rfc2904>.

   [Sethi14]  Sethi, M., Oat, E., Di Francesco, M., and T. Aura, "Secure
              Bootstrapping of Cloud-Managed Ubiquitous Displays",
              Proceedings of ACM International Joint Conference on
              Pervasive and Ubiquitous Computing (UbiComp 2014), pp.
              739-750, Seattle, USA , September 2014,
              <http://dx.doi.org/10.1145/2632048.2632049>.

   [SimplePairing]
              Bluetooth, SIG, "Simple pairing whitepaper", Technical
              report , 2007.








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Appendix A.  Exchanges and events per state

   Figure 10 shows how the EAP server chooses the exchange type
   depending on the server and peer states.  In the state combinations
   marked with hyphen "-", there is no possible exchange and user action
   is required to make progress.  Note that peer state 4 is omitted from
   the table because the peer never connects to the server when the peer
   is in that state.


   +--------+---------------------------+------------------------------+
   | peer   | exchange chosen by        | next peer and                |
   | states | server                    | server states                |
   +========+===========================+==============================+
   | server state: Unregistered (0)                                    |
   +--------+---------------------------+------------------------------+
   | 0..2   | Initial Exchange          | both 1 (0 on error)          |
   | 3      | -                         | no change, notify user       |
   +--------+---------------------------+------------------------------+
   | server state: Waiting for OOB (1)                                 |
   +--------+---------------------------+------------------------------+
   | 0      | Initial Exchange          | both 1 (0 on error)          |
   | 1      | Waiting Exchange          | both 1 (no change on error)  |
   | 2      | Completion Exchange       | both 4 (no change on error)  |
   | 3      | -                         | no change, notify user       |
   +--------+---------------------------+------------------------------+
   | server state: OOB Received (2)                                    |
   +--------+---------------------------+------------------------------+
   | 0      | Initial Exchange          | both 1 (0 on error)          |
   | 1      | Completion Exchange       | both 4 (no change on error)  |
   | 2      | Completion Exchange       | both 4 (no change on error)  |
   | 3      | -                         | no change, notify user       |
   +--------+---------------------------+------------------------------+
   | server state: Reconnecting (3) or Registered (4)                  |
   +--------+---------------------------+------------------------------+
   | 0..2   | -                         | no change, notify user       |
   | 3      | Reconnect Exchange        | both 4 (3 on error)          |
   +--------+---------------------------+------------------------------+


              Figure 10: How server chooses the exchange type

   Figure 11 lists the local events that can take place in the server or
   peer.  Both the server and peer output and accept OOB messages in
   association state 1.  The OOB message events have been marked with
   asterisk (*) to indicate that events are only possible if allowed by
   the negotiated OOB directions (Dirp).  Communication errors and
   timeouts in states 0..2 lead back to state 0, while similar errors in



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   states 3..4 lead to state 3.  Application request for rekeying (e.g.
   to refresh session keys or to upgrade algorithms) also takes the
   association from state 3..4 to state 3.  User can always reset the
   association state to 0.  Recovering association data, e.g. from a
   backup, leads to state 3.


   +--------+---------------------------+------------------------------+
   | server/| possible local events     | next state                   |
   | peer   | on server and peer        |                              |
   | state  |                           |                              |
   +========+===========================+==============================+
   | 1      | OOB Output*               | 1                            |
   | 1      | OOB Input*                | 2 (1 on error)               |
   | 0..2   | Timeout/network failure   | 0                            |
   | 3..4   | Timeout/network failure   | 3                            |
   | 3..4   | Rekeying request          | 3                            |
   | 0..4   | User resets peer state    | 0                            |
   | 0..4   | Association state recovery| 3                            |
   +--------+---------------------------+------------------------------+


                Figure 11: Local events on server and peer

Appendix B.  Application-specific parameters

   Table 8 lists OOB channel parameters that need to be specified in
   each application that makes use of EAP-NOOB.  The list is not
   exhaustive and is included for the convenience of implementors only.






















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   +--------------------+----------------------------------------------+
   | Parameter          | Description                                  |
   +--------------------+----------------------------------------------+
   | OobDirs            | Allowed directions of the OOB channel        |
   |                    |                                              |
   | OobMessageEncoding | How the OOB message data fields are encoded  |
   |                    | for the OOB channel                          |
   |                    |                                              |
   | SleepTimeDefault   | Default minimum time in seconds that the     |
   |                    | peer should sleep before the next Waiting    |
   |                    | Exchange                                     |
   |                    |                                              |
   | OobRetries         | Number of received OOB messages with invalid |
   |                    | Hoob after which the receiver moves to       |
   |                    | Unregistered (0) state                       |
   |                    |                                              |
   | NoobTimeout        | How many seconds the sender of the OOB       |
   |                    | message remembers the sent Noob value. The   |
   |                    | RECOMMENDED value is 3600 seconds.           |
   |                    |                                              |
   | ServerInfoMembers  | Required members in ServerInfo               |
   |                    |                                              |
   | PeerInfoMembers    | Required members in PeerInfo                 |
   +--------------------+----------------------------------------------+

                   Table 8: OOB channel characteristics

Appendix C.  EAP-NOOB Roaming

   AAA architectures [RFC2904] allow for roaming of network-connected
   appliances that are authenticated over EAP.  While the peer is
   roaming in a visited network, authentication still takes place
   between the peer and an authentication server in its home network.
   EAP-NOOB supports such roaming by assigning a Realm to the peer.
   After the Realm has been assigned, the peer's NAI enables the visited
   network to route the EAP session to the peer's home AAA server.

   A peer device that is new or has gone through a hard reset should be
   connected first to the home network and establish an EAP-NOOB
   association with its home AAA server before it is able to roam.
   After that, it can perform the Reconnect Exchange from the visited
   network.

   Alternatively, the device may provide some method for the user to
   configure the Realm of the home network.  In that case, the EAP-NOOB
   association can be created while roaming.  The device will use the
   user-assigned Realm in the Initial Exchange, which enables the EAP
   messages to be routed correctly to the home AAA server.



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Appendix D.  OOB message as URL

   While EAP-NOOB does not mandate any particular OOB communication
   channel, typical OOB channels include graphical displays and emulated
   NFC tags.  In the client-to-server direction, it may be convenient to
   encode the OOB message as a URL, which is then encoded as a QR code
   for displays and printers or as an NDEF record for NFC tags.  A user
   can then simply scan the QR code or NFC tag and open the URL, which
   causes the OOB message to be delivered to the authentication server.
   The URL MUST specify the https protocol i.e. secure connection to the
   server, so that the man-in-the-middle attacker cannot read or modify
   the OOB message.

   The ServerInfo in this case includes a JSON member called "ServerUrl"
   of the following format with maximum length of 60 characters:

   https://<host>[:<port>]/[<path>]

   To this, the peer appends the OOB message fields (PeerId, Noob, Hoob)
   as a query string.  PeerId is provided to the peer by the server and
   might be a 22-character string.  The peer base64url encodes the
   16-byte values Noob and Hoob into 22-character strings.  The query
   parameters MAY be in any order.  The resulting URL is of the
   following format:

   https://<host>[:<port>]/[<path>]?P=<PeerId>&N=<Noob>&H=<Hoob>

   The following is an example of a well-formed URL encoding the OOB
   message (without line breaks):

   https://example.com/Noob?P=ZrD7qkczNoHGbGcN2bN0&N=rMinS0-F4EfCU8D9ljx
   X_A&H=QvnMp4UGxuQVFaXPW_14UW

Appendix E.  Example messages

   The message examples in this section are generated with Curve25519
   ECDH test vectors specified in section 6.1 of [RFC7748]
   (server=Alice, peer=Bob).  The direction of the OOB channel
   negotiated is 2 (server-to-peer).  The JSON messages are as follows
   (line breaks are for readability only).

   ====== Initial Exchange ======

   Identity response:
      noob@eap-noob.net

   EAP request (type 1):




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      {"Type":1,"Vers":[1],"PeerId":"qJjnijxpojI0dti6qGfOIb","Cryptosuit
      es":[1],"Dirs":3,"ServerInfo":{"Name":"Example","Url":"https://exa
      mple.com/Noob"},"realm":"noob.example.com"}

   EAP request (type 1):
      {"Type":1,"Vers":[1],"PeerId":"qJjnijxpojI0dti6qGfOIb","Cryptosuit
      es":[1],"Dirs":3,"ServerInfo":{"Name":"Example","Url":"https://exa
      mple.com/Noob"},"realm":"noob.example.com"}

   EAP response (type 1):
      {"Type":1,"Verp":1,"PeerId":"qJjnijxpojI0dti6qGfOIb","Cryptosuitep
      ":1,"Dirp":2,"PeerInfo":{"Make":"Acme","Type":"None","Serial":"DU-
      8448","SSID":"Noob2","BSSID":"6c:19:8f:83:c2:90"}}

   EAP request (type 2):
      {"Type":2,"PeerId":"qJjnijxpojI0dti6qGfOIb","Ns":"1htC1L24K-
      jkP9bEgDAEnnmK44ltlY1XwKooEOxs-5c","jwk":{"kty":"EC","crv":"Curve2
      5519","x":"MCowBQYDK2VuAyEAhSDwCYkwp1R0i33ctD73Wg2_Og0mOBr066Spjqq
      bTmo"},"SleepTime":60}

   EAP response (type 2):
      {"Type":2,"PeerId":"qJjnijxpojI0dti6qGfOIb","Np":"ppe-KZ_-Xdz8bwEb
      _vfnny2dKkMepFbiLgf3xduVxxo","jwk":{"kty":"EC","crv":"Curve25519",
      "x":"MCowBQYDK2VuAyEA3p7bfXt9wbTTW2HC7OQ1Nz-DQ8hbeGdNrfx-FG-
      IK08"}}

   ====== Waiting Exchange ======

   Identity response:
      qJjnijxpojI0dti6qGfOIb+s1@noob.example.com

   EAP request (type 3):
      {"Type":3,"PeerId":"qJjnijxpojI0dti6qGfOIb","SleepTime":60}

   EAP response (type 3):
      {"Type":3,"PeerId":"qJjnijxpojI0dti6qGfOIb"}

   ====== OOB Step ======

   Identity response:
      data:,P=qJjnijxpojI0dti6qGfOIb&N=sqfpPmEXh4iPx23oY0t_Lg&H=Y2MxZDc2
      MDUzNTNkMTE3Mg

   ====== Completion Exchange ======

   Identity response:
      qJjnijxpojI0dti6qGfOIb+s2@noob.example.com




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   EAP request (type 8):
      {"Type":8,"PeerId":"qJjnijxpojI0dti6qGfOIb"}

   EAP response (type 8):
      {"Type":8,"PeerId":"qJjnijxpojI0dti6qGfOIb","NoobId":"NzMxMTNkZGFl
      NjhiMmNmYg"}

   EAP request (type 4):
      {"Type":4,"PeerId":"qJjnijxpojI0dti6qGfOIb","NoobId":"NzMxMTNkZGFl
      NjhiMmNmYg","MACs":"3Kf-OEE0l_SMC1C2XYdQmg"}

   EAP response (type 4):
      {"Type":4,"PeerId":"qJjnijxpojI0dti6qGfOIb","MACp":"z6G--
      hg8U3dhSwjYJ8xIFA"}

   ====== Reconnect Exchange ======

   Identity response:
      qJjnijxpojI0dti6qGfOIb+s3@noob.example.com

   EAP request (type 5):
      {"Type":5,"Cryptosuites":[1],"PeerId":"qJjnijxpojI0dti6qGfOIb","Se
      rverInfo":{"Name":"Example","Url":"https://example.com/Noob"}}

   EAP response (type 5):
      {"Type":5,"PeerId":"qJjnijxpojI0dti6qGfOIb","Cryptosuitep":1,"Peer
      Info":{"Make":"Acme","Type":"None","Serial":"DU-
      8448","SSID":"Noob2","BSSID":"6c:19:8f:83:c2:90"}}

   EAP request (type 6):
      {"Type":6,"PeerId":"qJjnijxpojI0dti6qGfOIb","Ns":"RPmLvG79U-
      GfBZTbzbaYMhC1hEE4_lj9SEtrLAct-3w"}

   EAP response (type 6):
      {"Type":6,"PeerId":"qJjnijxpojI0dti6qGfOIb","Np":"u7ecFNRibJ0PnOn2
      zIXmpZrNwlykbqzfyGWZeaRq1MQ"}

   EAP request (type 7):
      {"Type":7,"PeerId":"qJjnijxpojI0dti6qGfOIb","MACs":"EL4hd-
      PMY_RL9pmfZqRffg"}

   EAP response (type 7):
      {"Type":7,"PeerId":"qJjnijxpojI0dti6qGfOIb","MACp":"rjMw0xRebtOYWH
      bgcFeGEw"}







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Appendix F.  Version history

   o  Version 01:

      *  Fixed Reconnection Exchange.

      *  URL examples.

      *  Message examples.

      *  Improved state transition (event) tables.

   o  Version 02:

      *  Reworked the rekeying and key derivation.

      *  Increased internal key lengths and in-band nonce and MAC
         lengths to 32 bytes.

      *  Less data in the persistent EAP-NOOB association.

      *  Updated reference [NIST-DH] to Revision 2 (2013).

      *  Shorter suggested PeerId format.

      *  Optimized the example of encoding OOB message as URL.

      *  NoobId in Completion Exchange to differentiate between multiple
         valid Noob values.

      *  List of application-specific parameters in appendix.

      *  Clarified the equivalence of Unregistered state and no state.

      *  Peer SHOULD probe the server regardless of the OOB channel
         direction.

      *  Added new error messages.

      *  Realm is part of the persistent association and can be updated.

      *  Clarified error handling.

      *  Updated message examples.

      *  Explained roaming in appendix.

      *  More accurate definition of timeout for the Noob nonce.



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      *  Additions to security considerations.

Authors' Addresses

   Tuomas Aura
   Aalto University
   Aalto  00076
   Finland

   EMail: tuomas.aura@aalto.fi


   Mohit Sethi
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   EMail: mohit@piuha.net
































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