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Versions: 00 draft-ietf-lisp-sec

Network Working Group                                           F. Maino
Internet-Draft                                                V. Ermagan
Intended status: Experimental                              Cisco Systems
Expires: September 5, 2011                                   A. Cabellos
                                       Technical University of Catalonia
                                                               D. Saucez
                                                          O. Bonaventure
                                        Universite catholique de Louvain
                                                           March 4, 2011


                        LISP-Security (LISP-SEC)
                      draft-maino-lisp-sec-00.txt

Abstract

   This memo specifies LISP-SEC, a set of security mechanisms that
   provide origin authentication, integrity and anti-replay protection
   to LISP's EID-to-RLOC mapping data.  LISP-SEC also enables
   verification of authorization on EID prefix claims.

Requirements Language

   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].

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 5, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   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
   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.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  3
   3.  LISP-SEC Threat Model  . . . . . . . . . . . . . . . . . . . .  3
   4.  Protocol Operations  . . . . . . . . . . . . . . . . . . . . .  4
   5.  LISP-SEC Control Messages Details  . . . . . . . . . . . . . .  6
     5.1.  Encapsulated Control Message LISP-SEC Extensions . . . . .  6
     5.2.  Map-Reply LISP-SEC Extensions  . . . . . . . . . . . . . .  8
     5.3.  ITR Processing . . . . . . . . . . . . . . . . . . . . . . 10
     5.4.  Encrypting and Decrypting an OTK . . . . . . . . . . . . . 11
     5.5.  Map-Resolver Processing  . . . . . . . . . . . . . . . . . 12
     5.6.  Map-Server Processing  . . . . . . . . . . . . . . . . . . 12
       5.6.1.  Map-Server Processing in Proxy mode  . . . . . . . . . 13
     5.7.  ETR Processing . . . . . . . . . . . . . . . . . . . . . . 13
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
     6.1.  Mapping System Security  . . . . . . . . . . . . . . . . . 13
     6.2.  Random Number Generation . . . . . . . . . . . . . . . . . 14
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  HMAC functions . . . . . . . . . . . . . . . . . . . . . . 14
     7.2.  Key Wrap Functions . . . . . . . . . . . . . . . . . . . . 15
     7.3.  Key Derivation Functions . . . . . . . . . . . . . . . . . 15
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  Normative References . . . . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16















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1.  Introduction

   The Locator/ID Separation Protocol [I-D.ietf-lisp] defines a set of
   functions for routers to exchange information used to map from non-
   routable Endpoint Identifiers (EIDs) to routable Routing Locators
   (RLOCs).  If these EID-to-RLOC mappings, carried through Map-Reply
   messages, are transmitted without integrity protection, an adversary
   can manipulate them and hijack the communication, impersonate the
   requested EID or mount Denial of Service or Distributed Denial of
   Service attacks.  Also, if the Map-Reply message is transported
   unauthenticated, an adversarial LISP entity can overclaim an EID-
   prefix and maliciously redirect traffic directed to a large number of
   hosts.  A detailed description of "overclaiming" attack is provided
   in [I-D.saucez-lisp-security].

   This memo specifies LISP-SEC, a set of sceurity mechanisms that
   provide origin authentication, integrity and anti-replay protection
   to LISP's EID-to-RLOC mapping data.  LISP-SEC also enables
   verification of authorization on EID prefix claims, ensuring that the
   entity that provides the location for a given EID prefix is entitled
   to do so.


2.  Definition of Terms

      One-Time Key (OTK): An ephemeral randomly generated key that must
      be used for a single Map-Request/Map-Reply exchange.

      Encapsulated Control Message (ECM): A LISP control message that is
      prepended with an additional LISP header.  ECM is used by ITRs to
      send LISP control messages to a Map-Resolver, by Map-Resolvers to
      forward LISP control messages to a Map-Server, and by Map-
      Resolvers to forward LISP control messages to an ETR.

      Authentication Data (AD): Metadata that is included either in a
      LISP ECM header or in a Map-Reply message to support
      confidentiality, integrity protection, and verification of EID
      prefix authorization.

   For definitions of other terms, notably Map-Request, Map-Reply,
   Ingress Tunnel Router (ITR), Egress Tunnel Router (ETR), Map-Server
   (MS) and Map-Resolver (MR) please consult the LISP specification
   [I-D.ietf-lisp].


3.  LISP-SEC Threat Model

   LISP-SEC addresses the control plane threats, described in



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   [I-D.saucez-lisp-security], that target EID-to-RLOC mappings,
   including manipulations of Map-Request and Map-Reply messages, and
   malicious xTR EID overclaiming.  However LISP-SEC makes two main
   assumptions that are not part of [I-D.saucez-lisp-security].  First,
   the LISP Mapping System is expected to deliver Map-Request messages
   to their intended destinations as identified by the EID.  Second, no
   Man-in-the-Middle (MiM) attack can be mounted within the LISP Mapping
   System.

   Accordingly to the threat model described in
   [I-D.saucez-lisp-security] LISP-SEC assumes that any kind of attack,
   including MiM attacks, can be mounted in the access network, outside
   of the boundaries of the LISP mapping system.  An on-path attacker,
   outside of the LISP mapping service system can, for instance, hijack
   mapping requests and replies, spoofing the identity of a LISP node.
   Another example of on-path attack, called over claiming attack, can
   be mounted by a malicious Egress Tunnel Router (ETR), by over
   claiming the EID prefixes for which it is authoritative.  In this way
   the ETR can maliciously redirect traffic directed to a large number
   of hosts.


4.  Protocol Operations

   The goal of the security mechanisms defined in [I-D.ietf-lisp] is to
   prevent unauthorized insertion of mapping data, by providing origin
   authentication and integrity protection for the Map-Registration, and
   by using the nonce to detect unsolicited Map-Reply sent by off-path
   attackers.

   LISP-SEC builds on top of the security mechanisms defined in
   [I-D.ietf-lisp] to address the threats described in Section 3 by
   leveraging the trust relationships existing among the LISP entities
   participating to the exchange of the Map-Request/Map-Reply messages.
   Those trust relationships are used to securely distribute a One-Time
   Key (OTK) that provides origin authentication, integrity and anti-
   replay protection to mapping protocol data, and that effectively
   prevent over claiming attacks.  The processing of security parameters
   during the Map-Request/Map-Reply exchange is as follows:

   o  The OTK is generated and stored at the ITR, and securely
      transported to the Map-Server.

   o  The Map-Server uses the OTK to compute an HMAC that protects the
      integrity of the mapping data provided by the Map-Server to
      prevent overclaiming attacks.  The Map-Server also derives a new
      OTK (OTK-ETR), by applying a Key Derivation Function (KDF) to the
      original OTK, that is passed to the ETR.



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   o  The ETR uses the new OTK to compute an HMAC that protects the
      integrity of the Map-Reply sent to the ITR.

   o  Finally, the ITR uses the stored OTK to verify the integrity of
      the mapping data provided by both the Map-Server and the ETR, and
      to verify that no overclaiming attacks were mounted along the path
      between the Map-Server and the ITR.

   Section 5 provides the detailed description of the LISP-SEC control
   messages and their processing, while the rest of this section
   describes the flow of protocol operations at each entity involved in
   the Map-Request/Map-Reply exchange:

   o  The ITR, upon transmitting a Map-Request message, generates and
      stores an OTK.  This key is included into the Encapsulated Control
      Message (ECM) that contains the Map-Request sent to the Map-
      Resolver.  To provide OTK confidentiality over the path between
      the ITR and its Map-Resolver, the OTK SHOULD be encrypted using a
      preconfigured key shared between the ITR and the Map-Resolver,
      similar to the key shared between the ETR and the Map-Server in
      order to secure ETR registration [I-D.ietf-lisp-ms].

   o  The Map-Resolver decapsulates the ECM message, decrypts the OTK,
      if needed, and forwards through the Mapping System the received
      Map-Request and the OTK, as part of a new ECM message.  As
      described in Section 5.5, the LISP Mapping System delivers the ECM
      to the appropriate Map-Server, as identified by the EID
      destination address of the Map-Request.

   o  The Map-Server is configured with the location mappings and policy
      information for the ETR responsible for the destination EID
      address.  Using this preconfigured information the Map-Server,
      after the decapsulation of the ECM message, finds the longest
      match EID prefix that covers the requested EID in the received
      Map-Request.  The Map-Server adds this EID prefix, together with
      an HMAC computed using the OTK, to a new Encapsulated Control
      Message that contains the received Map-Request.

   o  The Map-Server derives a new OTK (OTK-ETR) by applying a Key
      Derivation Function (KDF) to the OTK.  This new OTK is included in
      the Encapsulated Control Message sent to the ETR.  To provide OTK
      confidentiality over the path between the Map-Server and the ETR,
      the new OTK should be encrypted using the key shared between the
      ETR and the Map-Server in order to secure ETR registration
      [I-D.ietf-lisp-ms].

   o  If the Map-Server is acting in proxy mode, as specified in
      [I-D.ietf-lisp], the ETR is not involved in the origination of the



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      Map-Reply.  In this case the Map-Server originates the Map-Reply
      on behalf of the ETR as described below.

   o  The ETR, upon receiving the Encapsulated Map-Request from the Map-
      Server, decrypts the OTK-ETR, if needed, and originates a Map-
      Reply that contains the EID-to-RLOC mapping information as
      specified in [I-D.ietf-lisp].

   o  The ETR computes an HMAC over the original LISP Map-Reply, keyed
      with OTK-ETR to protect the integrity of the whole Map-Reply.  The
      ETR also copies the EID prefix authorization data that the Map-
      Server included in the Encapsulated Map-Request into the Map-Reply
      message.

   o  The ITR, upon receiving the Map-Reply, uses the locally stored OTK
      to verify the integrity of the EID prefix authorization data
      included in the Map-Reply by the Map-Server.  The ITR computes
      OTK-ETR by applying the same KDF used by the Map-Server, and
      verifies the integrity of the Map-Reply.  If the integrity checks
      fail the Map-Reply MUST be discarded.  Also, if the EID prefix
      claimed by the ETR in the Map-Reply is less specific than the EID
      prefix authorization data inserted by the Map-Server, the ITR MUST
      discard the Map-Reply.


5.  LISP-SEC Control Messages Details

   LISP-SEC metadata associated with a Map-Request is transported within
   the Encapsulated Control Message that contains the Map-Request.

   LISP-SEC metadata associated with the Map-Reply is transported within
   the Map-Reply itself.

5.1.  Encapsulated Control Message LISP-SEC Extensions

   LISP-SEC uses the ECM (Encapsulated Control Message) defined in
   [I-D.ietf-lisp] with Type set to 8, and S bit set to 1 to indicate
   that the LISP header includes Authentication Data (AD).  The format
   of the LISP-SEC ECM Authentication Data is defined in the following
   figure.  OTK-AD stands for One-Time Key Authentication Data and
   EID-AD stands for EID Authentication Data.










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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     AD Type   |V|  Reserved   |        Requested HMAC ID      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\
   |              OTK Length       |       OTK Encryption ID       | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   |                       One-Time-Key Preamble ...               | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ OTK-AD
   |                   ... One-Time-Key Preamble                   | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   ~                      One-Time Key (128 bits)                  ~/
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\
   |           EID AD Length       |           KDF ID              | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   |             Reserved          |         EID HMAC ID           | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   |   Reserved    | EID mask-len  |           EID-AFI             | EID-AD
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   ~                          EID prefix ...                       ~ |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   ~                       EID HMAC (160 bits)                     ~ |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/

                     LISP-SEC ECM Authentication Data

      AD Type: 1 (LISP-SEC Authentication Data)

      V: Key Version bit.  This bit is toggled when the sender switches
      to a new OTK wrapping key

      Reserved: Set to 0 on transmission and ignored on receipt.

      Requested HMAC ID: the HMAC algorithm requested by the ITR.  See
      Section 5.3 for details.

      OTK Length: The length (in bytes) of the OTK Authentication Data
      (OTK-AD), that contains the OTK Preamble and the OTK.

      OTK Encryption ID: The identifier of the key wrapping algorithm
      used to encrypt the One-Time-Key.  When a 128-bit OTK is sent
      unencrypted by the Map-Resolver, the OTK Encryption ID is set to
      NULL_KEY_WRAP_128.  See Section 5.4 for more details.

      One-Time-Key Preamble: set to 0 if the OTK is not encrypted.  When
      the OTK is encrypted, this field may carry additional metadata
      resulting from the key wrapping operation.  When a 128-bit OTK is
      sent unencrypted by Map-Resolver, the OTK Preamble is set to



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      0x0000000000000000 (64 bits).  See Section 5.4 for details.

      One-Time-Key: the OTK encrypted (or not) as specified by OTK
      Encryption ID.  See Section 5.4 for details.

      EID AD Length: length (in bytes) of the EID Authentication Data
      (EID-AD).  The ITR MUST set EID AD Length to 32, as it only fills
      the KDF ID field, and all the remaining fields part of the EID-AD
      are not present.

      KDF ID: Identifier of the Key Derivation Function used to derive
      OTK-ETR.  The ITR SHOULD use this field to indicate the
      recommended KDF algorithm, according to local policy.  The Map-
      Server can overwrite the KDF ID if it does not support the KDF ID
      recommended by the ITR.  See Section 5.4 for more details.

      Reserved: Set to 0 on transmission and ignored on receipt.

      EID HMAC ID: Identifier of the HMAC algorithm used to protect the
      integrity of the EID prefix authorization fields.  This field is
      filled by Map-Server that computed the EID prefix HMAC.  See
      Section 5.4 for more details.

      EID mask-len: Mask length for EID prefix.

      EID-AFI: Address family of EID-prefix according to [RFC5226]

      EID prefix: The Map-Server uses this field to specify the EID
      prefix that the destination ETR is authoritative for, and is the
      longest match for the requested EID.

      EID HMAC: HMAC of the EID prefix authorization fields that is
      computed and inserted by Map-Server.  Before computing the HMAC
      operation the EID HMAC field MUST be set to 0.  The HMAC covers
      the entire EID-AD.

5.2.  Map-Reply LISP-SEC Extensions

   LISP-SEC uses the Map-Reply defined in [I-D.ietf-lisp], with Type set
   to 2, and S bit set to 1 to indicate that the Map-Reply message
   includes Authentication Data (AD).  The format of the LISP-SEC Map-
   Reply Authentication Data is defined in the following figure.  LOC-AD
   stands for LOC Authentication Data.








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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    AD Type    |                 Reserved                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\
   |           EID AD Length       |           KDF ID              | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   |             Reserved          |         EID HMAC ID           | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   |   Reserved    | EID mask-len  |           EID-AFI             | EID-AD
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   ~                          EID prefix ...                       ~ |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   ~                       EID HMAC (160 bits)                     ~ |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/
   |         LOC AD Length         |         LOC HMAC ID           |\
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   ~                       LOC HMAC (160 bits)                     ~ LOC-AD
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/

                  LISP-SEC Map-Reply Authentication Data

      AD Type: 1 (LISP-SEC Authentication Data)

      EID AD Length: length (in bytes) of the EID-AD.

      KDF ID: Identifier of the Key Derivation Function used to derive
      OTK-ETR.  See Section 5.6 for more details.

      Reserved: Set to 0 on transmission and ignored on receipt.

      EID HMAC ID: Identifier of the HMAC algorithm used to protect the
      integrity of the EID prefix authorization fields.  See Section 5.6
      for more details.

      EID mask-len: Mask length for EID prefix.

      EID-AFI: Address family of EID-prefix according to [RFC5226].

      EID prefix: This field contains the EID prefix that the
      destination ETR is authoritative for, and is the longest match for
      the requested EID.

      EID HMAC: HMAC of the EID prefix authorization fields.  Before
      computing the HMAC operation the EID HMAC field MUST be set to 0.

      LOC AD Length: length (in bytes) of the Map-Reply Location
      Authentication Data (LOC-AD).



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      LOC HMAC ID: Identifier of the HMAC algorithm used to protect the
      integrity of the Map-reply Location Data.

      LOC HMAC: HMAC of the Map-reply Location Data.  The scope of the
      authentication covers the whole Map-Reply Payload (from Type to
      Mapping Protocol Data fields included).  See Section 5.7 for more
      details.

5.3.  ITR Processing

   Upon creating a Map-Request, the ITR generates a random OTK that is
   stored locally, together with the nonce generated as specified in
   [I-D.ietf-lisp].

   The Map-Request MUST be encapsulated in an ECM, with the S-bit set to
   1, to indicate the presence of Authentication Data.  If the ITR and
   the Map-Resolver are configured with a shared key, the OTK
   confidentiality SHOULD be protected by wrapping the OTK with the
   algorithm specified by the OTK Encryption ID field.  See Section 5.4
   for further details on OTK encryption.

   The Requested HMAC ID field contains the suggested HMAC algorithm to
   be used by the Map-Server and the ETR to protect the integrity of the
   ECM Authentication data and of the Map-Reply.

   The KDF ID field, specifies the suggested key derivation function to
   be used by the Map-Server to derive the OTK-ETR.

   The EID AD length is set to 32, since the Authentication Data does
   not contain EID prefix Authentication Data, and the EID-AD contains
   only the KDF ID field.

   In response to an encapsulated Map-Request that has the S-bit set, an
   ITR MUST receive a Map-Reply with the S-bit set, that includes an EID
   AD and a LOC AD.  If the Map-Reply does not include both ADs, the ITR
   MUST discard it.  In response to an encapsulated Map-Request with
   S-bit set to 0, the ITR expects a Map-Reply with S-bit set to 0, and
   the ITR SHOULD discard the Map-Reply if the S-bit is set.

   Upon receiving a Map-Reply, the ITR must verify the integrity of both
   the EID-AD and the LOC-AD, and MUST discard the Map-Reply if one of
   the integrity checks fails.

   The integrity of the EID-AD is verified using the locally stored OTK
   to re-compute the HMAC of the EID-AD using the Algorithm specified in
   the EID HMAC ID field.  If the EID HMAC ID field does not match the
   Requested HMAC ID the ITR SHOULD discard the Map-Reply and send a new
   Map-Request with a different Requested HMAC ID field, according to



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   ITR's local policy.  The ITR MUST set the EID HMAC ID field to 0
   before computing the HMAC.

   To verify the integrity of the LOC-AD, first the OTK-ETR is derived
   from the locally stored OTK using the algorithm specified in the KDF
   ID field.  This is because the LOC AD is generated by the ETR using
   the OTK-ETR.  If the KDF ID in the Map-Reply does not match the KDF
   ID requested in the Map-Request, the ITR SHOULD discard the Map-
   Reply, and send a new Map-Request with a different KDF ID, according
   to ITR's local policy.  The derived OTK-ETR is then used to re-
   compute the HMAC of the LOC-AD using the Algorithm specified in the
   LOC HMAC ID field.  If the LOC HMAC ID field does not match the
   Requested HMAC ID the ITR SHOULD discard the Map-Reply, and send a
   new Map-Request with a new Required HMAC ID according to ITR's local
   policy.

   The Map-Reply is considered a valid Map-Reply only if: (1) both
   EID-AD and LOC-AD are valid, and (2) the EID prefixes in the Map-
   Reply records are equal to or more specific than the EID prefix in
   the EID-AD.  After identifying the Map-Reply as valid, the ITR
   proceeds to adding the Map-Reply records to its EID-to-RLOC cache, as
   described in [I-D.ietf-lisp].

   The ITR SHOULD send SMR triggered Map Requests over the mapping
   system in order to receive a secure Map-Reply.  If an ITR accepts
   piggybacked Map-Replies, it SHOULD also send a Map-Request over the
   mapping system in order to securely verify the piggybacked Map-Reply.

5.4.  Encrypting and Decrypting an OTK

   If OTK confidentiality is required in the path between the Map-Server
   and the ETR, the OTK SHOULD be encrypted using the preconfigured key
   shared between the Map-Server and the ETR for the purpose of securing
   ETR registration [I-D.ietf-lisp-ms].  Similarly, if OTK
   confidentiality is required in the path between the ITR and the Map-
   Resolver, the OTK SHOULD be encrypted with a key shared between the
   ITR and the Map-Resolver.

   The OTK is encrypted using the algorithm specified in the OTK
   Encryption ID field.  When the AES Key Wrap algorithm is used to
   encrypt a 128-bit OTK, according to [RFC3339], the AES Key Wrap
   Initialization Value MUST be set to 0xA6A6A6A6A6A6A6A6 (64 bits).
   The output of the AES Key Wrap operation is 192-bit long.  The most
   significant 64-bit are copied in the One-Time Key Preamble field,
   while the 128 less significant bits are copied in the One-Time Key
   field of the LISP-SEC Authentication Data.

   When decrypting an encrypted OTK the receiver MUST verify that the



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   Initialization Value resulting from the AES Key Wrap decryption
   operation is equal to 0xA6A6A6A6A6A6A6A6.  If this verification fails
   the receiver MUST discard the entire message.

   When a 128-bit OTK is sent unencrypted the OTK Encryption ID is set
   to NULL_KEY_WRAP_128, and the OTK Preamble is set to
   0x0000000000000000 (64 bits).

5.5.  Map-Resolver Processing

   Upon receiving an encapsulated Map-Request with the S-bit set, the
   Map-Resolver decapsulates the ECM message.  The OTK, if encrypted, is
   decrypted as specified in Section 5.4.

   The Map-Resolver, as specified in [I-D.ietf-lisp-ms], originates a
   new ECM header with the S-bit set, that contains the unencrypted OTK,
   as specified in Section 5.4, and the other data derived from the ECM
   Authentication Data of the received encapsulated Map-Request.

   The Map-Resolver then forwards the received Map-Request, encapsulated
   in the new ECM header that includes the newly computed Authentication
   Data fields.

5.6.  Map-Server Processing

   Upon receiving an encapsulated Map-Request with the S-bit set, the
   Map-Server decapsulates the ECM and generates a new ECM
   Authentication Data.  The Authentication Data includes the OTK-AD and
   the EID-AD, that contains EID prefix authorization information, that
   are ultimately sent to the requesting ITR.

   The Map-Server updates the OTK-AD by deriving a new OTK (OTK-ETR)
   from the OTK received with the Map-Request.  OTK-ETR is derived
   applying the key derivation function specified in the KDF ID field.
   If the algorithm specified in the KDF ID field is not supported, the
   Map-Server uses a different algorithm to derive the key and updates
   the KDF ID field accordingly.

   The Map-Server and the ETR MUST be configured with a shared key for
   mapping registration according to [I-D.ietf-lisp-ms].  If OTK
   confidentiality is required, then the OTK-ETR SHOULD be encrypted, by
   wrapping the OTK-ETR with the algorithm specified by the OTK
   Encryption ID field as specified in Section 5.4.

   The Map-Server includes in the EID AD the longest match registered
   EID prefix for the destination EID, and an HMAC of this EID prefix.
   The HMAC is keyed with the OTK in the ECM Authentication Data that is
   received from ITR, and the HMAC algorithm is chosen according to the



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   Requested HMAC ID field.  If The Map-Server does not support this
   algorithm, the Map-Server uses a different algorithm and specifies it
   in the EID HMAC ID field.  The scope of the HMAC operation covers the
   entire EID-AD, from the EID-AD Length field to the EID HMAC field,
   which must be set to 0 before the computation.

   The Map-Server then forwards the updated ECM encapsulated Map-
   Request, that contains the OTK-AD, the EID-AD, and the received Map-
   Request to an authoritative ETR as specified in [I-D.ietf-lisp].

5.6.1.  Map-Server Processing in Proxy mode

   If the Map-Server is in proxy mode, it generates a Map-Reply, as
   specified in [I-D.ietf-lisp], with the S-bit set to 1.  The Map-Reply
   includes the Authentication Data that contains the EID AD, computed
   as specified in Section 5.6, as well as the LOC-AD computed as
   specified in Section 5.7.

5.7.  ETR Processing

   Upon receiving an encapsulated Map-Request with the S-bit set, the
   ETR decapsulates the ECM message.  The OTK field, if encrypted, is
   decrypted as specified in Section 5.4 to obtain the unencrypted OTK-
   ETR.

   The ETR then generates a Map-Reply as specified in [I-D.ietf-lisp]
   and includes an Authentication Data that contains the EID-AD, as
   received in the encapsulated Map-Request, as well as the LOC-AD.

   The EID-AD is copied from the Authentication Data of the received
   encapsulated Map-Request.

   The LOC-AD contains the HMAC of the whole Map-Reply message, keyed
   with the OTK-ETR and computed using the HMAC algorithm specified in
   the Requested HMAC ID field of the received encapsulated Map-Request.
   If the ETR does not support the Requested HMAC ID, it uses a
   different algorithm and updates the LOC HMAC ID field accordingly.
   Finally the ETR sends the Map-Reply to the requesting ITR as
   specified in [I-D.ietf-lisp].


6.  Security Considerations

6.1.  Mapping System Security

   The LISP-SEC threat model described in Section 3, assumes that the
   LISP Mapping System is working properly and eventually delivers Map-
   Request messages to a Map-Server that is authoritative for the



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   requested EID.

   Security is not yet embedded in LISP+ALT but BGP route filtering
   SHOULD be deployed in the ALT infrastructure to enforce proper
   routing in the mapping system.  The SIDR working group is currently
   addressing prefix and route advertisement authorization and
   authentication for BGP.  While following SIDR recommendations in the
   global Internet will take time, applying these recommendations to the
   ALT, which relies on BGP, should be less complex, as ALT is currently
   small and with a limited number of operators.  Ultimately, deploying
   the SIDR recommendations in ALT further ensures that the fore
   mentioned assumption is true.

   It is also assumed that no man-in-the-middle attack can be carried
   out against the ALT router to ALT router tunnels, and that the
   information included into the Map-Requests, in particular the OTK,
   cannot be read by third-party entities.  It should be noted that the
   integrity of the Map-Request in the ALT is protected by BGP
   authentication, and that in order to provide OTK confidentiality in
   the ALT mapping system the ALT router to ALT router tunnels MAY be
   deployed using GRE+IPSec.

6.2.  Random Number Generation

   The OTK MUST be generated by a properly seeded pseudo-random (or
   strong random) source.  See [RFC4086] for advice on generating
   security-sensitive random data


7.  IANA Considerations

7.1.  HMAC functions

   The following HMAC ID values are defined by this memo for use as
   Requested HMAC ID, EID HMAC ID, and LOC HMAC ID in the LISP-SEC
   Authentication Data:


             Name                     Number        Defined In
             -------------------------------------------------
             NONE                     0
             AUTH-HMAC-SHA-1-160      1             [RFC2104]
             AUTH-HMAC-SHA-256-128    2             [RFC4634]

             values 2-65535 are reserved to IANA.

                              HMAC Functions




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   AUTH-HMAC-SHA-1-160 MUST be supported, AUTH-HMAC-SHA-256-128 should
   be supported.

7.2.  Key Wrap Functions

   The following OTK Encryption ID values are defined by this memo for
   use as OTK key wrap algorithms ID in the LISP-SEC Authentication
   Data:

             Name                     Number        Defined In
             -------------------------------------------------
             NULL-KEY-WRAP-128        1
             AES-KEY-WRAP-128         2             [RFC3394]

             values 0 and 3-65535 are reserved to IANA.

                            Key Wrap Functions

   NULL-KEY-WRAP-128, and AES-KEY-WRAP-128 MUST be supported.

   NULL-KEY-WRAP-128 is used to carry an unencrypted 128-bit OTK, with a
   64-bit preamble set to 0x0000000000000000 (64 bits).

7.3.  Key Derivation Functions

   The following KDF ID values are defined by this memo for use as KDF
   ID in the LISP-SEC Authentication Data:

             Name                     Number        Defined In
             -------------------------------------------------
             NONE                     0
             HKDF-SHA1-128            1             [RFC5869]

             values 2-65535 are reserved to IANA.

                         Key Derivation Functions

   HKDF-SHA1-128 MUST be supported


8.  Acknowledgements

   The authors would like to acknowledge Pere Monclus, Dave Meyer, Dino
   Farinacci, Brian Weis, David McGrew, Darrel Lewis and Landon Curt
   Noll for their valuable suggestions provided during the preparation
   of this document.





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9.  Normative References

   [I-D.ietf-lisp]
              Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)",
              draft-ietf-lisp-10 (work in progress), March 2011.

   [I-D.ietf-lisp-interworking]
              Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
              "Interworking LISP with IPv4 and IPv6",
              draft-ietf-lisp-interworking-01 (work in progress),
              August 2010.

   [I-D.ietf-lisp-ms]
              Fuller, V. and D. Farinacci, "LISP Map Server",
              draft-ietf-lisp-ms-06 (work in progress), October 2010.

   [I-D.saucez-lisp-security]
              Saucez, D., Iannone, L., and O. Bonaventure, "LISP
              Security Threats", draft-saucez-lisp-security-02 (work in
              progress), January 2011.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              February 1997.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3394]  Schaad, J. and R. Housley, "Advanced Encryption Standard
              (AES) Key Wrap Algorithm", RFC 3394, September 2002.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
              Key Derivation Function (HKDF)", RFC 5869, May 2010.










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Authors' Addresses

   Fabio Maino
   Cisco Systems
   170 Tasman Drive
   San Jose, California  95134
   USA

   Email: fmaino@cisco.com


   Vina Ermagan
   Cisco Systems
   170 Tasman Drive
   San Jose, California  95134
   USA

   Email: vermagan@cisco.com


   Albert Cabellos
   Technical University of Catalonia
   c/ Jordi Girona s/n
   Barcelona,   08034
   Spain

   Email: acabello@ac.upc.edu


   Damien Saucez
   Universite catholique de Louvain
   Place St. Barbe 2
   Louvain-la-Neuve,
   Belgium

   Email: damien.saucez@uclouvain.be


   Olivier Bonaventure
   Universite catholique de Louvain
   Place St. Barbe 2
   Louvain-la-Neuve,
   Belgium

   Email: olivier.bonaventure@uclouvain.be






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