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
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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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