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INTERNET DRAFT                                                  T. Polk
Intended Status: Informational                                     NIST
                                                             R. Housley
                                                         Vigil Security
Expires: May 12, 2011                                  November 8, 2010


Routing Authentication Using A Database of Long-Lived Cryptographic Keys
                draft-polk-saag-rtg-auth-keytable-05.txt


Status of this Memo

   This Internet-Draft is submitted to IETF 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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   Internet-Drafts.

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   The list of Internet-Draft Shadow Directories can be accessed at
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Abstract

   This document describes the application of a database of long-lived
   cryptographic keys to establish session-specific cryptographic keys
   to support authentication services in routing protocols.  Keys may be
   established between two peers for pair-wise communications, or
   between groups of peers for multicast traffic.












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Table of Contents

   1  Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 2
      1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . . 2
   2 Architecture and Design . . . . . . . . . . . . . . . . . . . . . 3
   3 Pair-wise Application . . . . . . . . . . . . . . . . . . . . . . 3
   4 Identifier Mapping  . . . . . . . . . . . . . . . . . . . . . . . 5
      4.1 Selected Range Reservation . . . . . . . . . . . . . . . . . 6
      4.2 Protocol Specific Mapping Tables . . . . . . . . . . . . . . 6
   5 Database Maintenance  . . . . . . . . . . . . . . . . . . . . . . 6
   6 Worked Examples . . . . . . . . . . . . . . . . . . . . . . . . . 6
      6.1 Worked Example: TCP-AO . . . . . . . . . . . . . . . . . . . 7
         6.1.1 Setup . . . . . . . . . . . . . . . . . . . . . . . . . 7
         6.1.2 Protocol Operation: Xp Initiates a Connection . . . . . 8
         6.1.3 Protocol Operation: Yp Initiates a Connection . . . . . 9
      6.2 Worked Example: IS-IS  . . . . . . . . . . . . . . . . . . . 9
         6.2.1 Setup . . . . . . . . . . . . . . . . . . . . . . . .  10
         6.2.2 Protocol Operations . . . . . . . . . . . . . . . . .  14
            6.2.2.1 Sending a Hello Message  . . . . . . . . . . . .  14
            6.2.2.2 Receiving a Hello Message  . . . . . . . . . . .  15
            6.2.2.3 Generating a Link State PDU  . . . . . . . . . .  15
            6.2.2.4 Receiving a Link State PDU . . . . . . . . . . .  16
            6.2.2.5 Sending a Sequence Number PDU  . . . . . . . . .  16
            6.2.2.6 Receiving a Sequence Number PDU  . . . . . . . .  16
   7  Security Considerations  . . . . . . . . . . . . . . . . . . .  16
   8  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  17
   9  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  17
   10  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
      10.1  Normative References . . . . . . . . . . . . . . . . . .  17
      10.2  Informative References . . . . . . . . . . . . . . . . .  17
   Author's Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18
   Full Copyright Statement  . . . . . . . . . . . . . . . . . . . .  19

1  Introduction

   This document describes the application of a database of long-lived
   cryptographic keys, as defined in [KEYTAB], to establish session-
   specific cryptographic keys to provide authentication services in
   routing protocols.  Keys may be established between two peers for
   pair-wise communications, or between groups of peers for multicast
   traffic.


1.1  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 RFC 2119 [RFC2119].



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2 Architecture and Design

   Figure 1 illustrates the establishment and use of cryptographic keys
   for authentication in routing protocols.  Long-lived cryptographic
   keys are inserted in a database manually.  In the future, we
   anticipate an automated key management protocol to insert these keys
   in the database. (While this future environment conceivably includes
   automated key management protocols to negotiate short-lived
   cryptographic session keys, such keys are out of scope for this
   database.)  The structure of the database of long-lived cryptographic
   keys is described in [KEYTAB].

   The cryptographic keying material for individual sessions is derived
   from the keying material stored in the database of long-lived
   cryptographic keys.  A key derivation function (KDF) and its inputs
   are named in the database of long-lived cryptographic keys; session
   specific values based on the routing protocol are input the the KDF.
   Protocol specific key identifiers may be assigned to the
   cryptographic keying material for individual sessions if needed.

      +--------------+   +----------------+
      |              |   |                |
      |  Manual Key  |   | Automated Key  |
      | Installation |   | Mgmt. Protocol |
      |              |   |                |
      +------+-------+   +--+----------+--+
             |              |          |
             |              |          |
             V              V          |<== Out of scope for this model.
      +------------------------+       |    Often used in other
      |                        |       |    protocol environments
      | Long-lived Crypto Keys |       |    like IPsec and TLS.
      |                        |       |
      +------------+-----------+       |
                   |                   |
                   |                   |
                   V                   V
        +---------------------------------+
        |                                 |
        | Short-lived Crypto Session Keys |
        |                                 |
        +---------------------------------+

          Figure 1.  Cryptographic key establishment and use.


3 Pair-wise Application




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   Figure 2 illustrates how the long-lived cryptographic keys are
   accessed and employed when an entity wishes to establish a protected
   session with a peer.  As one step in the initiation process, the
   initiator requests the set of long term keys associated with the peer
   for the particular protocol.  If the set contains more than one key,
   the initiator selects one long-term key based on the local policy.
   The long-term key is provided as an input, along with session-
   specific information (e.g., ports or initial counters), to a key
   derivation function.  The result is session-specific key material
   which is used to generate cryptographic authentication.

   Where the initiator is establishing a multicast session, the Peer in
   the key request identifies the set of systems that will receive this
   information.

                          +-------------------------+
                          |                         |
                          |        Long-Lived       |
                          |        Crypto Keys      |
                          |                         |
                          +-+---------------------+-+
                            ^                     |
                            |                     |
                            |                     V
                    +-------+-------+     +-------+-------+
                    |               |     |               |
                    |  Lookup Keys  |     |  Select Key   |
                    |    By Peer    |     |   By Policy   |
                    |  and Protocol |     |               |
                    |               |     +-------+-------+
                    +-------+-------+             |
                            ^                     |
                            |                     V
                            |             +-------+-------+
                            |             |               |
                            |             |  Session Key  |
                            |             |   Derivation  |
                            |             |               |
                            |             +-------+-------+
                            |                     |
                            |                     |
                    +-------+-------+             V
                    |               |     +-------+-------+
                    |   Initiate    |     |               |
                    |     Session   |     |Authentication |
                    |   with Peer   |     |   Mechanism   |
                    |               |     |               |
                    +---------------+     +---------------+



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                      Figure 2. Session Initiation

   Figure 3 illustrates how the long-lived cryptographic keys are
   accessed and employed when an entity receives a request establish a
   protected session with a peer.   As step one in the session
   establishment process, the receiver extracts the keyID for the long-
   term keyID from the received data.  The receiver then requests the
   specified long-term key from the table. The long-term key is provided
   as an input, along with session-specific information (e.g., ports or
   initial counters), to a key derivation function.  The result is
   session-specific key material which is used to verify the
   cryptographic authentication information.

                          +-------------------------+
                          |                         |
                          |        Long-Lived       |
                          |        Crypto Keys      |
                          |                         |
                          +-+---------------------+-+
                            ^                     |
                            |                     |
                            |                     V
                    +-------+-------+     +-------+-------+
                    |               |     |               |
                    |  Lookup Key   |     |  Session Key  |
                    |    By KeyID   |     |   Derivation  |
                    |               |     |               |
                    +-------+-------+     +-------+-------+
                            ^                     |
                            |                     |
                            |                     V
                    +-------+-------+     +-------+-------+
                    |               |     |               |
                    | Receive Data  |     |Authentication |
                    |    From Peer  |     |   Mechanism   |
                    |               |     |               |
                    +---------------+     +---------------+

                      Figure 3. Session Acceptance

4 Identifier Mapping

   [KEYTAB] specifies a 16-bit identifier, but protocols already exist
   with key identifiers of various sizes.  Where the identifiers are of
   different sizes, an extra mapping step may be required.  Note that
   mapping mechanisms are local - that is, different mapping mechanisms
   could be employed on different peers.




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   In practice, the mapping process need only be applied to the
   LocalKeyID, whose value must be unique in the context of the
   database, as defined in [KEYTAB].  Uniqueness is not required for the
   PeerKeyID, so mapping is generally restricted to truncation.  Mapping
   would only be needed to expand PeerKeyID's value beyond 16 bits.

4.1 Selected Range Reservation

   Where a protocol uses an index of less than 16 bits, a selected range
   of the local index space can be reserved for a particular protocol.
   For example, consider two protocols P1 and P2 that each use 8 bit key
   identifiers.   Without identifier mapping these protocols would share
   the space {0x0000 through 0x00ff} which would limit the pair of
   protocols to 256 keys in total.  By reserving the ranges {0x7f00
   through 0x7fff} and {0x7e00 through 0x7eff} for P1 and P2
   respectively permits each protocol to use the full 256 key
   identifiers and establishes an unambiguous mapping for the protocol
   key identifiers and local table identifiers.

   When an initiator selects a key from the set in the table, the given
   key identifier needs to be masked or shifted to the on-the-wire
   range.  Before requesting a specific key, the receiver would use a
   shim layer to map the on-the-wire identifier into the reserved range.

4.2 Protocol Specific Mapping Tables

   Each protocol can also maintain a simple mapping table with two
   fields: the 16 bit index and the protocol specific value:

   KEYTAB index (16 bits)   |  Protocol specific index (8 bits)

   In this case, the host system would maintain separate mapping tables
   for protocols P1 and P2.

5 Database Maintenance

   The previous sections focus upon installing and using the
   cryptographic keys in the database.  A mechanism or mechanisms to
   remove unneeded keys is also needed to ensure that the key material
   up-to-date. [KEYTAB] provides mechanisms for expiration of entries;
   such key management could be performed in a fully automated fashion.
   Other reasons for key removal, such as severing a business
   relationship, or deciding a long lived key has been compromised
   before its expiration date, would inherently require a manual key
   removal process.

6 Worked Examples




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6.1 Worked Example: TCP-AO

   This section describes the way a TCP-AO implementation could use the
   database. [tcpao] TCP-AO protocol is an example where the key
   identifier is limited to 8 bits, so an identifier mapping is needed.

   We will assume two peers Xp and Yp.  Xp employs the range reservation
   method for mapping and has reserved the range {0x7f00 ... 0x7fff} for
   LocalKeyIDs for TCP-AO, mapping to {0x00 ... 0xff}.   Yp employs a
   protocol specific mapping table in its TCP-AO implementation.

   The following subsections describe how peers Xp and Yp make use of
   the database of long-lived cryptographic keys when Xp and Yp
   respectively initiate a session.  (Note: Rollover to new sessions
   keys during a session is described in [tcpao].)

6.1.1 Setup

   The owners of Xp and Yp determine a need for authenticated
   communication using TCP-AO. They decide to use AES-CMAC-128 for
   authentication, so a 128 bit key is needed.  They decide to use the
   same key for both directions (inbound and outbound), and that the key
   will be available from 12/31/2010 through 12/31/2011. Through an out-
   of-band channel, the administrators establish the shared secret:

        0x0123456789ABCDEF0123456789ABCDEF

   Peer Xp selects the first available TCP-AO identifier in the reserved
   range, which is 0x7f05 and maps to an eight-bit identifier 0x05.
   Peer Yp selects the next available TCP-AO identifier, 0x12, and the
   next available LocalKeyID, which is 0x0107.  Peer Yp also adds an
   entry to its TCP-AO mapping table mapping the LocalKeyID to the TCP-
   AO identifier, as shown in Figure 5:

   LocalKeyID     TCP-AO identifier
   --------------------------------
   0x001a      |    0x01
   0x004d      |    0x02
     ...            ...
   0x0107      |    0x12

   Figure 5. Protocol Specific KeyID Mapping Table for TCP-AO

   After exchanging the TCP-AO identifiers, the peers have sufficient
   information to establish their [KEYTAB] entries.  Peer Xp's [KEYTAB]
   entry is shown as Figure 6:

   LocalKeyID   0x7f05



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   PeerKeyID    0x0012
   KDF          ????
   KDFInputs    none
   AlgID        AES-CMAC-128
   Key          0x0123456789ABCDEF0123456789ABCDEF
   Direction    both
   NotBefore    12/31/2010
   NotAfter     12/31/2011
   Peers        yp.example.com
   Protocol     TCP-AO

   Figure 6. Key Table Entry on Xp

   Peer Yp's [KEYTAB] entry is shown as Figure 6:

   LocalKeyID   0x0107
   PeerKeyID    0x0005
   KDF          ????
   KDFInputs    none
   AlgID        AES-CMAC-128
   Key          0x0123456789ABCDEF0123456789ABCDEF
   Direction    both
   NotBefore    12/31/2010
   NotAfter     12/31/2011
   Peers        xp.example.com
   Protocol     TCP-AO

   Figure 7. Key Table Entry on Yp

6.1.2 Protocol Operation: Xp Initiates a Connection

   Peer Xp wishes to initiate a connection with Peer Yp.

   (1) Xp performs a key lookup for {Peer=Yp, Protocol=TCP-AO}, and the
   entry with LocalKeyID 0x7f05 is returned.
   (2) The LocalKeyID 0x7f05 is range mapped by Xp to the TCP-AO
   identifier 0x05.
   (3) Xp performs the session key derivation using the mechanism
   specified for the TCP-AO protocol in [ao-crypto].
   (4) Xp generates the AES-CMAC-128 MACs for the outgoing traffic using
   the derived key, and asserts the key identifier 0x05 in the packets.
   (5) Yp receives a protected packet from Xp, and extracts the key
   identifier 0x05.
   (6) Yp performs a a key lookup for {Peer=Xp, Protocol=TCP-AO,
   PeerKeyID=0x05}, and the entry with LocalKeyID 0x0107 is returned.
   (7) Yp performs the session key derivation using the mechanism
   specified for the TCP-AO protocol in [ao-crypto].
   (8) Yp verifies the MACs for the incoming traffic using the derived



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   key.

6.1.3 Protocol Operation: Yp Initiates a Connection

   Where Peer Yp establishes the connection, the same process is
   followed, except that the range mapping process from step (2) is
   replaced by a table lookup.

6.2 Worked Example: IS-IS

   This section describes the way an IS-IS implementation supporting the
   IS-IS generic cryptographic authentication mechanism could use the
   database. [isis] [rfc1195] [rfc5310] IS-IS is an interior gateway
   protocol (IGP) that can be used to support IP as well as OSI.

   IS-IS routers are grouped into "areas". Routers establish adjacencies
   with their neighboring routers and share link state information
   through flooding. Information shared within an area is termed Level 1
   information, and information shared between areas is termed level 2
   information. An IS-IS router can be Level 1, Level 2, or both
   (designated as Level 1/2). Level 1 routers only form Level 1
   adjacencies with other Level 1 or Level 1/2 routers within their own
   area. Level 2 or Level 1/2 routers can form adjacencies with other
   Level 2 or Level 1/2 routers in other areas as well as their own
   area.

   An IS-IS deployment can have multiple Level 1 areas; Level 1 areas
   are differentiated by area addresses that are unique within the IS-IS
   deployment.  (An IS-IS deployment has only a single Level 2 domain
   which is formed from all the Level 2 and Level 1/2 routers within the
   routing domain, irrespective of their area addresses.)

   The IS-IS protocol supports routers that are connected by LANs and
   point-to-point links.  Level 1 and Level 2 messages on a LAN are
   differentiated by the broadcast address.  Point-to-Point links may be
   configured as Level 1, Level 2, or both.

   This worked example describes how an IS-IS router, denoted Rp, makes
   use of the database for the following eight cases:
   * sending a LAN IS to IS Hello PDU
   * receiving a LAN IS to IS Hello PDU
   * sending a Point-to-Point IS to IS Hello PDU
   * receiving a Point-to-Point IS to IS Hello PDU
   * sending a Link State Packet
   * receiving a Link State Packet
   * sending sequence number PDUs
   * receiving sequence number PDUs




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   In this example, Rp is a Level 1/2 router. Rp has two LAN interfaces;
   on the first interface (eth0) Rp is connected to other Level 1
   routers; on the second interface (eth1) Rp is connected to both other
   Level 1 and Level 2 routers by a LAN.  Rp is also connected to one
   additional Level 1 router, Rq, by a point-to-point link (ppp1).  The
   Level 1 area that Rp participates in has an area address of:

       0x4922

   The IS-IS protocol supports routers that are connected by LANs and
   point-to-point links.  Level 1 and Level 2 messages on a LAN are
   differentiated by the broadcast address.  The implementation will use
   the following multicast addresses:

      Level 1: 01-80-C2-00-00-14
      Level 2: 01-80-C2-00-00-15

   The authentication mechanism specified in RFC 5310 uses a 16 bit key
   identifier which matches the key table, so the identifier can be used
   directly.

   In this example, an interior router Rp makes use of the database of
   long-lived cryptographic keys to manage its IS-IS long-term keys.  Rp
   participates in both Level 1 and Level 2.

   (For this example, we will use a single area address for each area.
   Note that multiple area addresses can be supported for each area.)

   In addition to the area addresses that specify the set of recipients,
   six octet system IDs are used to uniquely identify the sender.  The
   system ID is required to be unique within the area, and in practice
   is derived from a MAC address. Rp has the following system ID

       0x123456

   The Network Entity Title (or NET) is constructed from the system ID
   and the area.  Rp has the following NET:

       Level 1 Area: 0x4922123456

6.2.1 Setup

   The owners of the IS-IS system determine a need for authenticated
   communication between the interior gateways. They decide to use HMAC-
   SHA1 for authentication with 128 bit keys.

   For routers that only participate in Level 1, there are two long-term
   keys: one for hello traffic, and a second for link state PDUs.  For



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   routers that participate in both Level 1 and Level 2, two additional
   long-term keys are required: again, the two keys are used to protect
   hellos and LSPs, respectively.  The owners decide these keys will be
   available from 12/31/2010 through 12/31/2011. Through an out-of-band
   channel, the administrators establish the following shared secrets:

   * a pairwise key for each point-to-point link to protect hello
   messages;

   * a multicast key for each broadcast LAN interface for each Level to
   protect hello messages;

   * a multicast key for LSP and sequence number packets for each Level
   1 area; and

   * a multicast key for LSP and sequence number packets for the Level 2
   domain.

   Since Rp will send Level 1 hellos on two LANs and a point-to-point
   link, and Level 2 hellos on one LAN, it will be configured with four
   IS-IS hello keys.  These keys are specified in Figures 8 through 11,
   respectively.


      Level 1 hello traffic: 0x0123456789ABCDEF0123456789ABCDEF
      Level 1 link state PDUs: 0x123456789ABCDEF0123456789ABCDEF0
      Level 2 hello traffic: 0x23456789ABCDEF0123456789ABCDEF01
      Level 2 link state PDUs: 0x3456789ABCDEF0123456789ABCDEF012

   Since the three LAN hello keys are for multicast traffic, the leading
   bit of the LocalKeyID is required to be 1. PeerkeyID is set to group.
    There is a pairwsie key for the point-to-point hellos (in Figure
   10),  Since there is no concept of a session, key diversification is
   not needed.  This implies there is no kdf or kdf inputs, and the
   long-term key is used directly to protect the messages.  The
   algorithm id indicates hmac sha1, and the direction is both inbound
   and outbound.

   The key generator selects the first available IS-IS identifier.  For
   a new implementation, any value may be selected.  Otherwise, the key
   identifiers can not collide with currently assigned values for IS-IS
   keys.  Since Rp participates at both Level 1 and Level 2, Rp installs
   all four keys. Rp's [KEYTAB] entries are shown as Figures 8 through
   11:

   LocalKeyID   0x7101
   PeerKeyID    group
   KDF          none



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   KDFInputs    none
   AlgID        HMAC-SHA-1
   Key          0x0123456789ABCDEF0123456789ABCDEF
   Interface    eth0
   Direction    both
   NotBefore    12/31/2010
   NotAfter     12/31/2011
   Peers        0x4922
   Protocol     IS-IS Hello L1

   Figure 8. Key Table Entry on Rp for Level 1 LAN Hellos on eth0

   (use ppp1)

   LocalKeyID   0x7102
   PeerKeyID    0x7102
   KDF          none
   KDFInputs    none
   AlgID        HMAC-SHA-1
   Key          0x123456789ABCDEF0123456789ABCDEF0
   Interface    eth1
   Direction    both
   NotBefore    12/31/2010
   NotAfter     12/31/2011
   Peers        0x4922
   Protocol     IS-IS Hello L1

   Figure 9. Key Table Entry on Rp for Level 1 LAN Hellos on eth1

   LocalKeyID   0x0003
   PeerKeyID    0x0105
   KDF          none
   KDFInputs    none
   AlgID        HMAC-SHA-1
   Key          0x23456789ABCDEF0123456789ABCDEF01
   Interface    ppp1
   Direction    both
   NotBefore    12/31/2010
   NotAfter     12/31/2011
   Peers        0x4922
   Protocol     IS-IS Hello L1

   Figure 10. Key Table Entry on Rp for Level 1 point-to-point Hellos

   LocalKeyID   0x7103
   PeerKeyID    group
   KDF          none
   KDFInputs    none



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   AlgID        HMAC-SHA-1
   Key          0x3456789ABCDEF0123456789ABCDEF012
   Interface    eth1
   Direction    both
   NotBefore    12/31/2010
   NotAfter     12/31/2011
   Peers        0x4922
   Protocol     IS-IS Hello L2

   Figure 11. Key Table Entry on Rp for Level 2 Hellos on eth1

   Rp also requires two multicast keys for flooding Link State Packets
   and transmitting Sequence number packets.  The first key is shared
   throughout the Level 1 Area 0x4922; the second key is shared amongst
   the routers in the Level 2 domain. Rp's [KEYTAB] entries for the two
   multicast LSP/sequence number packet keys are shown as Figures 12 and
   13:

   LocalKeyID   0x7104
   PeerKeyID    group
   KDF          none
   KDFInputs    none
   AlgID        HMAC-SHA-1
   Key          0x456789ABCDEF0123456789ABCDEF0123
   Interface    *
   Direction    both
   NotBefore    12/31/2010
   NotAfter     12/31/2011
   Peers        0x4922
   Protocol     IS-IS LSP L1

   Figure 12. Key Table Entry on Rp for Level 1 LSPs and Sequence Number
   packets

   LocalKeyID   0x7105
   PeerKeyID    group
   KDF          none
   KDFInputs    none
   AlgID        HMAC-SHA-1
   Key          0x56789ABCDEF0123456789ABCDEF01234
   Interface    *
   Direction    both
   NotBefore    12/31/2010
   NotAfter     12/31/2011
   Peers        IS-IS L2
   Protocol     IS-IS LSP L2

   Figure 13. Key Table Entry on Rp for Level 1 LSPs and Sequence Number



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   packets

6.2.2 Protocol Operations

   The following subsections describe how an IS-IS router makes use of
   the database for the following four cases:
   * sending a Hello message
   * receiving a Hello message
   * sending a Link State Packet
   * receiving a Link State Packet
   * sending a sequence number PDU
   * receiving a sequence number PDU

6.2.2.1 Sending a Hello Message

   Rp wishes to send a Hello message.  Because Rp is configured with
   three Level 1 interfaces, and one Level 2 interface, four different
   hello messages will be transmitted.  Each message is protected with
   the key IS-IS Hello key for that interface and level.

   For each LAN interface:

   (1) Rp performs a key lookup for the interface (e.g., eth0 or eth1)
   with the protocol "IS-IS Hello L1".
   (2) Rp parses the key entry and determines the algorithm attribute
   (in this example, the algorithm attribute is always HMAC-SHA1).
   (3) Rp constructs the outgoing LAN Hello PDU.  If replay protection
   is a concern, Rp includes a timestamp with the local time.  (The
   timestamp would would be contained in a new TLV.  Such a TLV has not
   been specified at this time.)
   (4) Rp generates the SHA1-HMAC for the outgoing LAN Hello using the
   long-term key, and asserts the appropriate key identifier in the RFC
   5310 authentication mechanism TLV.
   (5) Rp transmits the Hello message on the LAN interface using the
   Level 1 multicast MAC address.

   For the point-to-point HELLO:

   (1) Rp performs a key lookup for the interface (ppp1) and protocol
   "IS-IS Hello L1".
   (2) Rp parses the key entry and determines the algorithm attribute
   (i.e., HMAC-SHA1).
   (3) Rp constructs the outgoing point-to-point Hello PDU.  If replay
   protection is a concern, Rp includes a timestamp with the local time.
   (4) Rp generates the SHA1-HMAC for the outgoing point-to-point LAN
   Hello using the long-term key, and asserts the key identifier in the
   RFC 5310 authentication mechanism TLV.
   (5) Rp transmits the Hello message over the point-to-point link.



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6.2.2.2 Receiving a Hello Message

   Rp processes hello messages by the following algorithm:

   (1) Rp parses the RFC 5310 authentication mechanism TLV and performs
   a key lookup using the included PeerKeyID.
   (2) Rp parses the key entry and
      (a) Rp verifies the keyID is associated with this interface.  If
      the interface does not match, the sender or receiver is
      misconfigured.  An alarm is triggered and the hello is discarded.
      Otherwise, continue with (2)(b).
      (b) Rp determines the algorithm attribute (in this case, HMAC-
      SHA1).
   (3) Rp calculates the SHA1-HMAC and compares it to the value in the
   Hello. If the HMACs do not match, the message is discarded.
   (Otherwise proceed to step 4.)
   (4) Rp checks the timestamp state for the sender.  (If the timestamp
   value is NULL, proceed to 6.  If there is a timestamp value for this
   sender, proceed to step 7).
   (5) Rp extracts the timestamp, if any, and compares it to the value
   in the Hello.  If the timestamp is earlier than the stored timestamp,
   or no timestamp was present, the Hello message is discarded.  If the
   timestamp is later than the stored timestamp, update the stored value
   and process the Hello message.
   (6) Process the hello message.

   [Note that there is no different in processing for LAN or Point-to-
   point hellos.]

6.2.2.3 Generating a Link State PDU

   Rp wishes to send a link state PDU to the other routers.  To perform
   this task, Rp constructs two separate LSPs, protected by its Level 1
   and Level 2 LSP keys. The LSPs are transmitted to each neighbor that
   has formed an adjacency with Rp as appropriate.  (Level 1 LSPs are
   ONLY transmitted over links which have a Level 1 adjacency, and
   similarly Level 2 LSPs only over links which have Level 2
   adjacencies.)


   (1) Rp performs a key lookup for protocol "IS-IS L1 Flood".   (The
   entry with PeerKeyID 0x7104 is returned.)
   (2) Rp parses the key entry and determines the algorithm attribute
   (HMAC-SHA1).
   (3) Rp constructs the Level 1 link state PDU. Note that this includes
   a sequence number.
   (4) Rp generates the appropriate MAC for the outgoing LSP using the
   long-term key, and asserts the key identifier 0x7104 in the RFC 5310



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   authentication mechanism TLV.
   (5) Rp transmits the LSP to all current L1 neighboring adjacencies.

   The process is repeated for Level 2, beginning with a key lookup for
   protocol "IS-IS L2 Flood"".  Note that the Level 2 link state PDU
   constructed in step (3) will contain different information than the
   Level 1 LSP.

6.2.2.4 Receiving a Link State PDU

   Rp processes incoming link state PDUs by the following algorithm:

   (1) Rp parses the RFC 5310 authentication mechanism TLV and performs
   a key lookup using the PeerKeyID.
   (2) Rp parses the key entry and determines the algorithm attribute
   (HMAC-SHA1)
   (3) Rp calculates the SHA1-HMAC and compares it to the value in the
   link state PDU. If the HMACs do not match, the message is discarded.
   (Otherwise proceed to step 4.)
   (4) Rp performs IS-IS processing to ensure the message is fresh
   (e.g., checks the sequence number for the sender.) If Rp already has
   fresher information, Rp will discard the packet, then construct an
   LSP with the fresher information and forward it to the sender.
   Otherwise, perform step 5.
   (5) Rp forwards the verified Link State PDU to all neighbors with the
   same level except the neighbor that transmitted the PDU.  (That is,
   Level 1 Link State PDUs are forwarded to Level 1 neighbors; Level 2
   Link State PDUs are forwarded to Level 2 neighbors.)

6.2.2.5 Sending a Sequence Number PDU

   The cryptographic process for protecting a Sequence Number PDU is the
   same as those specified for LSPs in 6.2.2.3.  Note that there is no
   difference when sending partial or full link state PDUs.


6.2.2.6 Receiving a Sequence Number PDU

   The cryptographic process for authenticating a Sequence Number PDU is
   the same as those specified for LSPs in 6.2.2.4.

7  Security Considerations

   The "hello" message processing examples assume the existence of a
   timestamp extension to provide replay protection.  Sequence numbers
   for hello messages would provide an alternative solution; the authors
   selected a timestamp since this imposes no state on the sender.  Time
   synchronization is not needed to achieve replay protection; receivers



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   that desire replay protection simply retain the timestamp from the
   previous hello for comparison.

   By requiring an IS-IS router to begin using timestamps immediately
   upon key change, or not at all, step (x) in 6.2.2.2 could have been
   omitted.  By verifying that previous messages did not have a
   timestamp, a receiver prevents replay of a past hello message that
   did not include timestamps that was protected with the current key.

   The timestamp was omitted from the point-to-point hello in the
   example based on an assumption of physically protected media. If that
   is not the case, the timestamp could be included in these messages as
   well.


8  IANA Considerations

   This document requires no actions by IANA.


9  IANA Considerations

   Mike Shand was amazingly patient and helpful, demystifying and
   explaining IS-IS.  The authors are grateful for his assistance.  Any
   remaining mistakes in section 6.2 are the responsibility of the
   authors, of course!

10  References

10.1  Normative References

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

   [KEYTAB]   R. Housley and Polk, T. "Database of Long-Lived
               Cryptographic Keys", draft-housley-saag-crypto-key-table-
               04.txt, October 2010.


10.2  Informative References

   [tcpao]   J. Touch, Mankin A., and Bonica R. "The TCP Authentication
               Option", draft-ietf-tcpm-tcp-auth-opt-08.txt, October
               2009.

   [ao-crypto]   Lebovitz, G., "Cryptographic Algorithms, Use, &
               Implementation Requirments for TCP Authentication
               Option", draft-lebovitz-ietf-tcpm-tcp-ao-crypto-02.txt,



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               July 2009.

   [rfc1195]   Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
               dual environments", RFC 1195, December 1990.

   [isis]   International Organization for Standardization,
               "Intermediate system to Intermediate system intra-domain
               routeing information exchange protocol for use in
               conjunction with the protocol for providing the
               connectionless-mode Network Service (ISO 8473)", ISO/IEC
               10589:2002, Second Edition, Nov 2002.

   [rfc5310]   M. Bhatia, Manral, V., Li, T., Atkinson, R., White, R.
               and Fanto, M. "IS-IS Generic Cryptographic
               Authentication", RFC 5310, February 2009


Author's Addresses


   Tim Polk
   National Institute of Standards and Technology
   100 Bureau Drive, Mail Stop 8930
   Gaithersburg, MD 20899-8930
   USA
   EMail: tim.polk@nist.gov

   Russell Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA
   EMail: housley@vigilsec.com


















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