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-00.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 Task Force (IETF), its areas, and its working
groups. Note that other groups may also distribute working
documents as Internet-Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on March 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect 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.
Bhatia, Manav Standards Track [Page 1]
Internet-Draft September 2010
Abstract
Currently OSPFv3 uses IPSec for authenticating the protocol
packets. This draft proposes an alternative Generic
Authentication that can be used so that OSPFv3 does 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.
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
2. Basic Operation...............................................4
3. OSPFv3 Security Association...................................4
4. Authentication Procedure......................................6
4.1. Generic Authentication Header............................6
4.2. Cryptographic Authentication Procedure...................8
4.3. Cryptographic Aspects....................................8
4.4. Procedures at the Sending Side..........................10
4.5. Procedures at the Receiving Side........................10
5. Generic Authentication Mechanism.............................11
6. Security Considerations......................................11
7. IANA Considerations..........................................12
8. References...................................................12
8.1. Normative References....................................12
8.2. Informative References..................................12
1. Introduction
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.
Bhatia, Manav Expires March 2011 [Page 2]
Internet-Draft September 2010
[RFC4552] describes how IPv6 AH/ESP extension headers can be
used to provide authentication/confidentiality to OSPFv3.
There however are some environments (mobile ad-hoc), where IPSec
is difficult to configure and maintain, and this mechanism
cannot be used.
[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. While this
problem can be solved by employing certain implementation
tricks, it is an issue that should get addressed.
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.
Bhatia, Manav Expires March 2011 [Page 3]
Internet-Draft September 2010
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].
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.
Bhatia, Manav Expires March 2011 [Page 4]
Internet-Draft September 2010
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.
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.
Bhatia, Manav Expires March 2011 [Page 5]
Internet-Draft September 2010
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:
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
Bhatia, Manav Expires March 2011 [Page 6]
Internet-Draft September 2010
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
32-bit non-decreasing sequence number that is used to guard
against replay attacks.
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.
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 --------->|
Bhatia, Manav Expires March 2011 [Page 7]
Internet-Draft September 2010
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 OSPFv3 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 OSPFv3
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
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 OSPFv3 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
Bhatia, Manav Expires March 2011 [Page 8]
Internet-Draft September 2010
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 OSPFv3 packet's Generic Authentication Extension
Header
Data field is filled with the value Apad.
Then, a first hash, also known as the inner hash, is computed
as follows:
First-Hash = H(Ko XOR Ipad || (OSPFv3 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
Bhatia, Manav Expires March 2011 [Page 9]
Internet-Draft September 2010
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 OSPFv3 packet
as transmitted on the wire.
4.4. Procedures at the Sending Side
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. 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.
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
The appropriate OSPFv3 SA is identified by looking at the Key ID
from the Generic Authentication extension header from the
incoming OSPFv3 protocol packet
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.
Bhatia, Manav Expires March 2011 [Page 10]
Internet-Draft September 2010
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.
An implementation MAY have a transition mode where it includes
the Generic Authentication extension header in the packets but
does not verify this information. This is provided as a
transition aid for networks in the process of migrating to the
new generic authentication based authentication schemes.
5. Generic Authentication Mechanism
The extension header described in this document can also be used
by any other 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
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.
There is a transition mode suggested where routers can ignore
the Generic Authentication extension header information carried
in the protocol packets. The operator must ensure that this mode
is only used when migrating to the new Generic Authentication
based scheme as this leaves the router vulnerable to an attack.
Bhatia, Manav Expires March 2011 [Page 11]
Internet-Draft September 2010
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.
[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.
[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.
Bhatia, Manav Expires March 2011 [Page 12]
Internet-Draft 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.
[crypto-issues] Bhatia, M., et. al., " Issues with existing
Cryptographic Protection Methods for Routing
Protocols", Work in Progress
Author's Addresses
Manav Bhatia
Alcatel-Lucent
Bangalore
India
Phone:
Email: manav.bhatia@alcatel-lucent.com
Bhatia, Manav Expires March 2011 [Page 13]