KARP Working Group Manav Bhatia
Internet Draft Alcatel-Lucent
Intended status: Standards Track
Expires: March, 2011 September 2010
Non IPSec Authentication mechanism for OSPFv3
draft-bhatia-karp-non-ipsec-ospfv3-auth-01.txt
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Bhatia, Manav Standards Track [Page 1]
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Abstract
Currently a few routing protocols use IPSec for authenticating
their protocol packets. There are known issues with using IPSec
with the routing protocols and this draft proposes an
alternative Generic Authentication mechanism that can be used so
that these protocols do not depend upon IPSec for security. The
mechanism introduced in this draft is generic and can be used by
any protocol that currently uses IPSec for authentication.
While this mechanism is generic, this draft specifically looks
at OSPFv3 and how it can use the mechanism described herein.
Conventions used in this document
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]
Table of Contents
1. Introduction..................................................2
1.1. OSPFv3...................................................3
2. Basic Operation...............................................5
3. OSPFv3 Security Association...................................5
4. Authentication Procedure......................................6
4.1. Generic Authentication Header............................6
4.2. Cryptographic Authentication Procedure...................9
4.3. Cryptographic Aspects...................................10
4.4. Procedures at the Sending Side for OSPFv3...............11
4.5. Procedures at the Receiving Side for OSPFv3.............12
5. Generic Authentication Mechanism.............................12
6. Security Considerations......................................12
7. IANA Considerations..........................................13
8. References...................................................13
8.1. Normative References....................................13
8.2. Informative References..................................13
1. Introduction
Routing protocols like Open Shortest Path First Version 3
(OSPFv3) and Protocol Independent Multicast Sparse Mode (PIM-
SIM) (for the link-local messages) use IPSec [RFC4301] to ensure
authentication of their control packets.
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There however are some environments (mobile ad-hoc), where IPSec
is difficult to configure and maintain, and this mechanism
cannot be used.
The anti-replay feature available in both Authentication Header
(AH) [RFC4302] and Encapsulating Security Payload (ESP)
[RFC4303] is disabled by the receiver for a manually keyed
Security Association (SA). This means that the Anti-Replay
Window as described in [RFC4301] is completely ignored when
receiving IPSec packets.
Since routing protocols mostly use manually keyed SAs, they
cannot make use of the Anti-Reply feature provided by IPSec.
This makes the protocols vulnerable to replay attacks.
Routing protocols need IPSec for data integrity and rarely
employ it for confidentiality, therefore most specifications
[RFC4552] [RFC5796] that describe how routing protocols need to
use IPSec for security mandate using ESP-NULL.
So while the routing protocols could be using ESP-NULL, which
means that routing packets are being sent in clear, there is no
deterministic way to differentiate between encrypted and
unencrypted ESP packets by simply examining the packet. This can
pose some challenge to a device that wants to prioritize certain
control traffic over the other. IP Security Maintenance and
Extensions (IPSecME) Working group has documented two approaches
to enable intermediate security devices to distinguish between
encrypted and unencrypted ESP traffic - Wrapped Encapsulating
Security Payload (WESP) [RFC5840] and the heuristics approach
[RFC5879].
While this issue of traffic prioritization on the receiving
nodes can be solved by employing certain implementation tricks,
it is an issue that should get addressed.
This draft provides a generic mechanism that routing protocols
can use for data integrity verification while fixing the above
stated issues.
1.1. OSPFv3
Unlike OSPF (Open Shortest Path First) Version 2 [RFC2328] OSPF
for IPv6 (OSPFv3) [RFC5340], does not have Auth Type and
Authentication fields in its headers for authenticating the
protocol packets. It instead relies on the IPv6 Authentication
Header (AH) [RFC4302] and IPv6 Encapsulating Security Payload
(ESP) [RFC4303] to provide integrity, authentication, and/or
confidentiality.
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[RFC4552] describes how IPv6 AH/ESP extension headers can be
used to provide authentication/confidentiality to OSPFv3.
[RFC4552] discusses, at length, the reasoning behind using
manually configured keys, rather than some automated key
management protocol such as IKEv2 [RFC5996]. The primary problem
is the lack of suitable key management mechanism, as OSPF
adjacencies are formed on a one-to-many basis and most key
management mechanisms are designed for a one-to-one
communication model. This forces the system administrator to use
manually configured security associations (SAs) and
cryptographic keys to provide the authentication and, if
desired, confidentiality services.
Regarding replay protection [RFC4552] states that:
As it is not possible as per the current standards to provide
complete replay protection while using manual keying, the
proposed solution will not provide protection against replay
attacks.
Since there is no replay protection provided there are a number
of vulnerabilities in OSPFv3 which have been discussed in
[crypto-issues].
These can be fixed if we move to a non IPSec method for
authenticating the OSPFv3 protocol packets.
Lastly, there is also an issue with using IPSec for
authenticating OSPFv3 packets where prioritizing certain
protocol packets over the others becomes difficult.
This draft proposes a new mechanism that works similar to OSPFv2
for providing authentication to the OSPFv3 packets and attempts
to solve the problems described above for OSPFv3.
Additionally this document describes how HMAC-SHA authentication
can be used for OSPFv3.
By definition, HMAC ([RFC2104], [FIPS-198]) requires a
cryptographic hash function. This document proposes to use any
one of SHA-1, SHA-256, SHA-384, or SHA-512 [FIPS-180-3] to
authenticate the OSPFv3 packets.
It is believed that [RFC2104] is mathematically identical to
[FIPS-198] and it is also believed that algorithms in [RFC4634]
are mathematically identical to [FIPS-180-3].
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2. Basic Operation
In order to provide authentication for OSPFv3 packets,
implementations MUST support the Generic Authentication
extension header described in the subsequent sections.
This will only be used to provide data integrity and cannot be
used for confidentiality. If the latter is required then
implementations MUST use ESP as described in [RFC4552].
Using this authentication scheme, a session key (either
statically configured or derived from some master key) is used
on all the routers attached to a common network. For each OSPFv3
protocol packet, this key is used to generate and verify a
"message digest". This digest is carried inside the Generic
Authentication extension header. The message digest is a one-way
function of the OSPFv3 protocol packet and the secret key. Since
the secret key is never sent over the network in the clear,
protection is provided against passive attacks [RFC1704].
The algorithms used to generate and verify the digest are
specified implicitly by the key. In addition, a non decreasing
sequence number is included in the Generic Authentication Header
carried along with each OSPFv3 protocol packet to protect
against replay attacks.
3. OSPFv3 Security Association
An OSPFv3 Security Association contains a set of parameters
shared between any two legitimate OSPFv3 speakers.
Parameters associated with an OSPFv3 SA:
Key Identifier (Key ID)
This is a 32-bit unsigned integer used to uniquely identify an
OSPFV3 SA, as manually configured by the network operator.
The receiver determines the active SA by looking at the Key ID
field in the incoming protocol packet.
The sender based on the active configuration, selects the
Security Association to use and puts the correct Key ID value
associated with the Security Association in the OSPFV3 protocol
packet. If multiple valid and active OSPFV3 Security
Associations exist for a given outbound interface at the time an
OSPFV3 packet is sent, the sender may use any of those security
associations to protect the packet.
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Using Key IDs makes changing keys while maintaining protocol
operation convenient. Each key ID specifies two independent
parts, the authentication protocol and the authentication key,
as explained below.
Normally, an implementation would allow the network operator to
configure a set of keys in a key chain, with each key in the
chain having fixed lifetime. The actual operation of these
mechanisms is outside the scope of this document.
Note that each key ID can indicate a key with a different
authentication protocol. This allows multiple authentication
mechanisms to be used at various times without disrupting an
OSPFv3 peering, including the introduction of new authentication
mechanisms.
Authentication Algorithm
This signifies the authentication algorithm to be used with the
OSPFv3 SA. This information is never sent in cleartext over the
wire. Because this information is not sent on the wire, the
implementer chooses an implementation specific representation
for this information.
At present, the following values are possible:
HMAC-SHA-1, HMAC-SHA-256, HMAC-SHA-384 and HMAC-SHA-512.
Authentication Key
This value denotes the cryptographic authentication key
associated with the OSPFv3 SA. The length of this key is
variable and depends upon the authentication algorithm specified
by the OSPFv3 SA.
4. Authentication Procedure
4.1. Generic Authentication Header
The Generic Authentication Header uses the Next_Header (TBD via
IANA) in the immediately preceding header, and has the following
format:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Header Len | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cryptographic Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Data (Variable) |
~ ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Padding (Optional) |
~ ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
Next Header
8 bit selector that identifies the type of header immediately
following the Generic Authentication Extension Header. Uses the
same values as the IPv6 Next Header field [RFC2460].
Header Len
8-bit selector that indicates the length in 8 octet units of the
extension header, not including the first 8 octets.
Reserved
16-bit reserved field. The value MUST be initialized to zero by
the sender, and MUST be ignored by the receiver.
Key ID
32-bit field that identifies the algorithm and the secret key
used to create the message digest carried inside the extension
header.
Cryptographic Sequence Number
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32-bit non-decreasing sequence number that is used to guard
against replay attacks. This provides a long term protection
however it is still possible to replay packets using this
mechanism until the sequence number changes. This field is
initialized to zero and is also set to zero whenever the
originating router state is transitioned to "Down" state.
Whenever a protocol packet carrying this extension header is
accepted as authentic, the receiving router, must update the
cryptographic sequence number that it maintains for the
originating router to the received packet's sequence number.
This specification does not provide a rollover procedure for
the cryptographic sequence number. When the cryptographic
sequence number that the router is sending hits the maximum
value, the router should reset the cryptographic sequence number
that it is sending back to 0. After this is done, the router's
neighbors will reject the router's protocol packets for some
period till the protocol employing the use of generic
authentication times out and tries reestablishing the
adjacencies. In case of OSPFv3 this period would be the
RouterDeadInterval. However, it is expected that most
implementations will use "seconds since reboot" (or "seconds
since 1960", etc.) as the cryptographic sequence number. Such
a choice will essentially prevent rollover, since the
cryptographic sequence number field is 32 bits in length.
A protocol that wants to use the Generic Extension header MAY
not use the Anti-Replay feature if it does not require it. In
such cases this field MUST be set to zero and MUST be ignored by
the receiving router.
Authentication Data
Variable data that is carrying the digest of the protocol
packet.
Padding
This MUST be used with IPv6 in order to preserve IPv6 8-octet
alignment. If HMAC-SHA-1 is being used as the authentication
algorithm then the authentication data is of 20 bytes. Add to
this 1 byte of the next header, 1 byte of the header length, the
2 reserved bytes, 4 bytes for the cryptographic sequence number
and 4 bytes of the Key ID and we get 32 bytes. Since this is
already aligned to an 8 octet boundary no padding is required.
However, if the authentication algorithm is HMAC-SHA-256 then
the total size comes to 44 bytes, which is not aligned. In this
case 4 bytes of padding is used.
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The following diagram illustrates the OSPFv3 packet before and
after applying this extension header.
Packet format before applying Generic Authentication Header:
+----------------+------------------------------+
|orig IP header | OSPFv3 Payload |
|(any options) | |
+----------------+------------------------------+
Packet format after applying Generic Authentication Header:
+----------------+--------------+------------------+
|orig IP header | Generic Auth | OSPFv3 Payload |
|(any options) | header | |
+----------------+--------------+------------------+
|<----------- integrity --------->|
4.2. Cryptographic Authentication Procedure
As noted earlier the algorithms used to generate and verify the
message digest are specified implicitly by the secret key. This
specification discusses the computation of Cryptographic
Authentication data when any of the NIST SHS family of
algorithms is used in the Hashed Message Authentication Code
(HMAC) mode.
The currently valid algorithms (including mode) for
Cryptographic Authentication include:
HMAC-SHA-1
HMAC-SHA-256
HMAC-SHA-384
HMAC-SHA-512
Of the above, implementations of this specification MUST include
support for at least:
HMAC-SHA-256
and SHOULD include support for:
HMAC-SHA-1
and MAY also include support for:
HMAC-SHA-384
HMAC-SHA-512
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4.3. Cryptographic Aspects
In the algorithm description below, the following nomenclature,
which is consistent with [FIPS-198], is used:
H is the specific hashing algorithm (e.g. SHA-256).
K is the Authentication Key for the routing protocol (OSPFv3 in
this case) security association.
Ko is the cryptographic key used with the hash algorithm.
B is the block size of H, measured in octets rather than bits.
Note that B is the internal block size, not the hash size.
For SHA-1 and SHA-256: B == 64
For SHA-384 and SHA-512: B == 128
L is the length of the hash, measured in octets rather than
bits.
XOR is the exclusive-or operation.
Opad is the hexadecimal value 0x5c repeated B times.
Ipad is the hexadecimal value 0x36 repeated B times.
Apad is the hexadecimal value 0x878FE1F3 repeated (L/4) times.
Implementation Note:
This definition of Apad means that Apad is always the same
length
as the hash output.
(1)Preparation of the Key
In this application, Ko is always L octets long.
If the Authentication Key (K) is L octets long, then Ko is
equal to K. If the Authentication Key (K) is more than L
octets long, then Ko is set to H(K). If the Authentication
Key (K) is less than L octets long, then Ko is set to the
Authentication Key (K) with zeros appended to the end of the
Authentication Key (K) such that Ko is L octets long.
(2)First Hash
First, the protocol packet's Generic Authentication Extension
Header Data field is filled with the value Apad.
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Then, a first hash, also known as the inner hash, is computed
as follows:
First-Hash = H(Ko XOR Ipad || (Protocol Packet))
(3)Second Hash
Then a second hash, also known as the outer hash, is
computed as follows:
Second-Hash = H(Ko XOR Opad || First-Hash)
(4)Result
The result Second-Hash becomes the authentication data that
is sent in the Authentication Data field of the Generic
Authentication extension header. The length of the
authentication data is always identical to the message
digest size of the specific hash function H that is being
used.
This also means that the use of hash functions with larger
output sizes will also increase the size of the protocol
packet as transmitted on the wire.
4.4. Procedures at the Sending Side for OSPFv3
An appropriate OSPFv3 SA is selected for use with an outgoing
OSPFv3 protocol packet. This is done based on the active key at
that instant. If OSPFV3 is unable to find an active key, then
the packet MUST be discarded.
If OSPFV3 is able to find the active key, then the key gives the
authentication algorithm (HMAC-SHA-1, HMAC-SHA-256, HMAC-SHA-384
or HMAC-SHA-512) that needs to be applied on the packet.
An implementation MUST construct a pseudo Generic Authentication
extension header before it begins the authentication process. It
must set the Next Header to 89, to indicate an OSPF packet (or
some other value if the Upper layer protocol is something else).
The authentication data is computed as explained in the previous
section.
The Header length is set as per the authentication algorithm
that is being used. It is, for example, set to 3 for
HMAC-SHA-1 and 5 for HMAC-SHA-256.
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The key ID and the cryptographic sequence number is filled.
Appropriate padding, based on the authentication algorithm being
employed, must be used.
The result of the authentication algorithm is placed in the
Authentication data.
4.5. Procedures at the Receiving Side for OSPFv3
The appropriate OSPFv3 SA is identified by looking at the Key ID
from the Generic Authentication extension header from the
incoming OSPFv3 protocol packet.
Using the RouterID carried in the OSPFv3 header, the correct
sending neighbor MUST be identified. If a cryptographic sequence
number is found in the Generic Extension Header and is less than
the cryptographic sequence number recorded in the sending
neighbor's data structure, that OSPFv3 packet MUST be discarded.
Implementations MAY want to log this event.
Authentication algorithm dependent processing needs to be
performed, using the algorithm specified by the appropriate
OSPFv3 SA for the received packet.
Before an implementation performs any processing it needs to
save the values of the Authentication Value field in the Generic
Authentication extension header.
It should then set the Authentication Value field with Apad
before the authentication data is computed. The calculated data
is compared with the received authentication data in the packet
and the packet is discarded if the two do not match. In such a
case, an error event SHOULD be logged.
5. Generic Authentication Mechanism
The extension header described in this document can be used by
any upper layer protocol that desires integrity protection. All
it needs to do is to compute the digest over that protocol
packet and carry it inside the Generic Authentication extension
header as described in this document.
6. Security Considerations
The document proposes extensions to OSPFv3 which would make it
more secure than what it is today. It does not provide
confidentiality as a routing protocol contains information
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that does not need to be kept secret. It does, however, provide
means to authenticate the sender of the packets which is of
interest to us.
It should be noted that authentication method described in this
document is not being used to authenticate the specific
originator of a packet, but is rather being used to confirm that
the packet has indeed been issued by a router which had access
to the password.
The mechanism described here is not perfect and does not need to
be perfect. Instead, this mechanism represents a significant
increase in the work function of an adversary attacking the
OSPFv3 protocol, while not causing undue implementation,
deployment, or operational complexity.
7. IANA Considerations
The Generic Authentication extension header number is assigned
by IANA out of the IP Protocol Number space (and as recorded at
the IANA web page at
http://www.iana.org/assignments/protocol-numbers) is: TBD.
8. References
8.1. Normative References
[RFC2119] Bradner, S.,"Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S., et. al, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC4301] Kent, S. and Seo, K., "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[FIPS-180-3] US National Institute of Standards & Technology,
"Secure Hash Standard (SHS)", FIPS PUB 180-3, October
2008.
[FIPS-198] US National Institute of Standards & Technology, "The
Keyed-Hash Message Authentication Code (HMAC)", FIPS
PUB 198, March 2002.
8.2. Informative References
[RFC1704] Haller, N. and R. Atkinson, "On Internet
Authentication", RFC 1704, October 1994.
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[RFC2104] Krawczk, H., "HMAC: Keyed-Hashing for Message
Authentication", RFC 2104, February 1997.
[RFC2328] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[RFC5340] Coltun, R., et. al., "OSPF for Ipv6", RFC 5340, July
2008
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC5996] Kaufman, C., et. al., "Internet Key Exchange Protocol
Version 2 (IKEv2)", RFC 5996, September 2010.
[RFC4552] Gupta, M. and Melam, N.,
"Authentication/Confidentiality for OSPFv3", RFC 4552,
June 2006
[RFC4634] Eastlake 3rd, D. and T. Hansen, "US Secure Hash
Algorithms (SHA and HMAC-SHA)", RFC 4634, July 2006.
[RFC5796] Atwood, W., Islam, S. and Siami, M, "Authentication
and Confidentiality in Protocol Independent Multicast
Sparse Mode (PIM-SM) Link-Local Messages", RFC 5796,
March 2010
[RFC5840] Grewal, K., Montenegro, G. and Bhatia, M., "Wrapped
Encapsulating Security Payload (ESP) for Traffic
Visibility", RFC 5840, April 2010
[RFC5879] Kivinen, T. and McDonald, D., "Heuristics for
Detecting ESP-NULL Packets", RFC 5879, May 2010
[crypto-issues] Bhatia, M., et. al., "Issues with existing
Cryptographic Protection Methods for Routing
Protocols", Work in Progress
Author's Addresses
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Manav Bhatia
Alcatel-Lucent
Bangalore
India
Phone:
Email: manav.bhatia@alcatel-lucent.com
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