One document matched: draft-ietf-opsec-igp-crypto-requirements-01.txt
Differences from draft-ietf-opsec-igp-crypto-requirements-00.txt
Internet Draft September 2010
Network Working Group Manav Bhatia
Internet Draft Alcatel-Lucent
Expires: March 28, 2011 Vishwas Manral
Intended Status: Informational IP Infusion
September 27, 2010
Cryptographic Authentication Algorithm Implementation
Requirements for Routing Protocols
draft-ietf-opsec-igp-crypto-requirements-01.txt
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Bhatia and Manral [Page 1]
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Abstract
The routing protocols Open Shortest Path First version 2 (OSPFv2),
Intermediate System to Intermediate System (IS-IS) and Routing
Information Protocol (RIP) currently define Clear Text and MD5
(Message Digest 5) methods for authenticating protocol packets.
Recently effort has been made to add support for the SHA (Secure Hash
Algorithm) family of hash functions for the purpose of authenticating
routing protocol packets for RIP, IS-IS and OSPF.
To encourage interoperability between disparate implementations, it
is imperative that we specify the expected minimal set of algorithms
thereby ensuring that there is at least one algorithm that all
implementations will have in common.
This document examines the current set of available algorithms with
interoperability and effective cryptographic authentication
protection being the principle considerations. Cryptographic
authentication of these routing protocols requires the availability
of the same algorithms in disparate implementations. It is desirable
that newly specified algorithms should be implemented and available
in routing protocol implementations because they may be promoted to
requirements at some future time.
Table of Contents
1. Introduction...................................................3
2. Intermediate System to Intermediate System (IS-IS).............4
2.1 Authentication Scheme Selection............................4
2.2 Authentication Algorithm Selection.........................5
3. Open Shortest Path First Version 2(OSPFv2).....................5
3.1 Authentication Scheme Selection............................5
3.2 Authentication Algorithm Selection.........................6
4. Open Shortest Path First Version 3 (OSPFv3)....................6
5. Routing Information Protocol Version 2 (RIPv2).................6
5.1 Authentication Scheme Selection............................7
5.2 Authentication Algorithm Selection.........................7
6. Routing Information Protocol for IPv6 (RIPng)..................8
7. Security Considerations........................................8
8. Acknowledgements...............................................9
9. IANA Considerations............................................9
10. References....................................................9
10.1 Normative References......................................9
10.2 Informative References...................................10
Author's Addresses...............................................10
Bhatia and Manral [Page 2]
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1. Introduction
Most routing protocols include three different types of
authentication schemes: Null authentication, Clear Text Password and
a Cryptographic Authentication scheme. Null authentication is
equivalent to having no authentication scheme at all.
In a clear text scheme, also known as, simple password scheme, the
password is exchanged in the clear on the network and anyone with
physical access to the network can learn the password and compromise
the integrity of the routing domain. While the Password scheme
protects from accidental establishment of routing session in a given
domain, it offers little additional protection.
In a cryptographic authentication scheme, routers share a secret key
which is used to generate a message authentication code for each of
the protocol packets. Today, message authentication codes often use
a keyed MD5 digest. The recent escalating series of attacks on MD5
raise concerns about its remaining useful lifetime. These attacks may
not necessarily result in direct vulnerabilities for keyed MD5
digests as message authentication codes because the colliding message
may not correspond to a syntactically correct protocol packet. There
is a however a need felt to deprecate MD5 [RFC1321] in favor of
stronger message authentication code algorithms.
In light of these considerations there have been proposals for adding
support of the SHA [SHS] family of hash algorithms for authenticating
routing protocol packets in RIP [RFC2453], IS-IS [ISO] [RFC1195] and
OSPF [RFC2328].
However, the nature of cryptography is that algorithmic
improvement is an ongoing process and as is the exploration and
refinement of attack vectors. An algorithm believed to be strong
today may be demonstrated to be weak tomorrow. Given this, the choice
of preferred algorithm should favor the minimization of the
likelihood of it being compromised quickly.
It should be recognized that preferred algorithm(s) will change over
time to adapt to the evolving threats. The selection of preferred
algorithms may well not be reflected in the base protocol
specification. As protocols are extended the preference for presently
stronger algorithms presents a problem both on the question of
interoperability of existing and future implementations with respect
to standards and operational preference for the configuration as
deployed. This document intends to provide guidance to implementers
in anticipation of operational preference.
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It is expected an implementation should support changing of Security
(Authentication) Keys. Changing Keys periodically is a good security
practice.
Implementations can support in-service key change so that no control
packets are lost. During such Key change more than one key can be
active for receiving packets for a session. Some protocols support
Key ID which allows the two ends of a session to have multiple keys
simultaneously for a session. Key change however is managed outside
the scope of the protocols themselves and can be done manually via
operator intervention, or dynamically based on some timer or a
security protocol.
2. Intermediate System to Intermediate System (IS-IS)
The IS-IS specification allows for authentication of its Protocol
Data Units (PDUs) via the authentication TLV (TLV 10) in the PDU. The
base specification had provisions only for clear text passwords. RFC
5304 [RFC5304] extends the authentication capabilities by providing
HMAC-MD5 authentication for IS-IS PDUs.
RFC 5310 [RFC5310] adds support for the use of the SHA family of hash
algorithms for authenticating IS-IS PDUs.
2.1 Authentication Scheme Selection
In order for IS-IS implementations to interoperate with the use of
security, they must support one or more authentication schemes in
common. This section specifies the preference for standards
conformant IS-IS implementations, which desire to utilize the
security feature.
The earliest interoperability requirement for authentication as
stated by [ISO] [RFC1195] required all implementations to support
Clear Text Password. This authentication scheme's utility is limited
to precluding the accidental introduction of a new IS into a
broadcast domain. We believe that operators should not use this
scheme as it provides no protection against an attacker with access
to the broadcast domain as anyone can determine the secret password
through inspection of the PDU. This mechanism does not provide any
significant level of security and should be avoided.
[RFC5304] mandates the use of HMAC-MD5 for cryptographically
authenticating the IS-IS PDUs. It is likely that this may get
deprecated in favor of the generic cryptographic authentication
scheme defined in [RFC5310] in the future deployments, so new
implementations should support this scheme.
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2.2
Authentication Algorithm Selection
For IS-IS implementations to interoperate, they must have support for
one or more authentication algorithms in common.
This section details the authentication algorithm requirements for
standards conformant IS-IS implementations.
[RFC5304] mandates the use of HMAC-MD5 for cryptographically
authenticating the IS-IS PDUs. It is likely that this may get
deprecated in favor of HMAC-SHA-1 as defined in [RFC5310] in the
future deployments, so new implementations should support this
algorithm.
Implementations may start providing support for HMAC-SHA-256/HMAC-
SHA-384/HMAC-SHA-512 as these algorithms may be necessary in the
future.
3.
Open Shortest Path First Version 2(OSPFv2)
OSPFv2 as defined in [RFC2328] includes three different types of
authentication schemes: Null authentication, simple password and
cryptographic authentication. Null authentication is semantically
equivalent to no authentication. In the simple password scheme of
authentication, the passwords are exchanged in the clear on the
network. Anyone with physical access to the network can learn the
password and compromise the security of the OSPFv2 domain.
In the cryptographic authentication scheme, the OSPFv2 routers on a
common network/subnet are configured with a shared secret which is
used to generate a keyed MD5 digest for each packet. A monotonically
increasing sequence number scheme is used to protect against replay
attacks.
RFC 5709 [RFC5709] adds support for the use of the SHA family of hash
algorithms for authentication of OSPFv2 packets.
3.1 Authentication Scheme Selection
For OSPF implementations to interoperate with the use of security,
they must have one or more authentication schemes in common. This
section specifies the preference for standards conformant OSPFv2
implementations, which desire to utilize the security feature.
While [RFC2328] mandates the use of NULL Authentication, its use is
deprecated in any context where the operator wishes to authenticate
the OSPFv2 packets in their network.
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Internet Draft September 2010
Similarly Simple Password, also mandatory per [RFC2328], should be
used when the operator only wants to preclude the accidental
introduction of a router into the domain. This scheme is not useful
when the operator wants to authenticate the OSPFv2 packets.
Cryptographic Authentication is a mandatory scheme as defined in
[RFC2328] and all conformant implementations must support this.
3.2
Authentication Algorithm Selection
For OSPFv2 implementations to interoperate, they must support one or
more cryptographic authentication algorithms in common.
[RFC2328] states that implementations must offer keyed MD5
authentication. It is likely that this will be deprecated in favor of
HMAC-SHA-1 and HMAC-SHA-256 [RFC5709] in future deployments, so new
implementations should support these algorithms.
Operators should consider migration to HMAC-SHA-256 if they desire a
stronger cryptographic algorithm for authentication of OSPFv2
packets.
Implementations may start providing support for HMAC-SHA-1/HMAC-SHA-
384/HMAC-SHA-512 [RFC5709] as these algorithms may be preferred in
the future.
4.
Open Shortest Path First Version 3 (OSPFv3)
OSPFv3 [RFC5340] relies on the IPv6 Authentication Header (AH)
[RFC4302] and IPv6 Encapsulating Security Payload (ESP) [RFC4303] in
order to provide integrity, authentication, and/or confidentiality.
[RFC4522] mandates the use of ESP for authenticating OSPFv3 packets.
The implementations could also provide support for using AH to
protect these packets.
The algorithm requirements for AH and ESP are described in [RFC4835]
and are not discussed here.
5.
Routing Information Protocol Version 2 (RIPv2)
RIPv2, originally specified in [RFC1388], then [RFC1723], has been
updated and published as STD56 [RFC2453]. If the Address Family
Identifier of the first (and only the first) entry in the RIPv2
message is 0xFFFF, then the remainder of the entry contains the
authentication information. The [RFC2453] version of the protocol
provides for authenticating packets using a simple password of not
more than 16 octets, in which the password is sent in clear.
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"RIP-2 MD5 Authentication" [RFC2082] added support for Keyed-MD5
authentication, where a digest is appended to the end of the RIP
packet. "RIPv2 Cryptographic Authentication" [RFC4822] obsoleted
[RFC2082] and added the SHA family of hash algorithms to the list of
cryptographic authentications that can be used to protect RIPv2,
whereas [RFC2082] previously specified only the use of Keyed MD5.
5.1
Authentication Scheme Selection
For RIPv2 implementations to interoperate with the use of security,
one or more authentication schemes must be supported in common. This
section specifies the preference for standards conformant RIPv2
implementations, which desire to utilize the security feature.
Simple Password is a mandatory to implement scheme as defined in
[RFC2453] and should only be used when the operator wishes to
preclude the accidental introduction of a RIP router into the domain.
This authentication scheme is useful, but not when the operator wants
to protect RIPv2 message exchange in a potentially hostile
environment.
[RFC2082] mandates the use of Keyed-MD5. However, [RFC2082] has been
obsoleted by [RFC4822] Cryptographic Authentication. Compliant
implementations must provide support for Keyed-MD5 but should
recognize that this is superseded by Cryptographic Authentication as
defined in [RFC4822].
Implementations should provide support for [RFC4822] Cryptographic
Authentication as it will likely be the preferred authentication
method in the future.
5.2 Authentication Algorithm Selection
For RIPv2 implementations to interoperate, one or more authentication
algorithms must be supported in common that can be used for
authentication.
The keyed MD5 algorithm in [RFC2082] and [RFC4822] must be
implemented. It is our belief that it will be superseded by HMAC-SHA-
1 also available in [RFC4822]. Keyed MD5 must be implemented for
interoperability purposes, but its use may be deprecated in the
future.
Implementations should provide support for HMAC-SHA-1 used in
preference to keyed MD5 the future.
Operators should consider migration to HMAC-SHA-1 if they want to use
stronger cryptographic algorithms for authenticating RIPv2 packets.
Bhatia and Manral [Page 7]
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Implementations should consider providing support for HMAC-SHA-
256/HMAC-SHA-384/HMAC-SHA-512 as these algorithms may be preferred in
the future.
6. Routing Information Protocol for IPv6 (RIPng)
RIPng [RFC2080] relies on the IPv6 AH and IPv6 ESP to provide
integrity, authentication, and/or confidentiality.
The algorithm requirements for AH and ESP are described in [RFC4835]
and are not discussed here.
7. Security Considerations
The cryptographic mechanisms referenced in this document provide only
authentication algorithms. These algorithms do not provide
confidentiality. Encrypting the content of the packet and thereby
providing confidentiality is not considered in the definition of the
routing protocols.
The cryptographic strength of the HMAC depends upon the cryptographic
strength of the underlying hash function and on the size and quality
of the key. The feasibility of attacking the integrity of routing
protocol messages protected by Digests may be significantly more
limited than that of other data, however preference for one family of
algorithms over another may also change independently of the
perceived risk to a particular protocol.
To ensure greater security, the keys used should be changed
periodically and implementations must be able to store and use more
than one key at the same time. Operational experience suggests that
the lack of periodic rekeying is a source of significant exposure and
that the lifespan of shared keys in the network is frequently
measured in years.
While simple password schemes are well represented in the document
series and in conformant implementations of the protocols, the
inability to offer either integrity or identity protection are
sufficient reason to strongly discourage their use.
This document concerns itself with the selection of cryptographic
algorithms for use in the authentication of routing protocol packets
being exchanged between adjacent routing processes. The
cryptographic algorithms identified in this document are not known to
be broken at the current time, and ongoing cryptographic research so
far leads us to believe that they will likely remain secure in the
foreseeable future. We expect that new revisions of this document
will be issued in the future to reflect current thinking on the
Bhatia and Manral [Page 8]
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algorithms various routing protocols should employ to ensure
interoperability between disparate implementations.
8. Acknowledgements
We would like to thank Joel Jaeggli for this comments and feedback on
this draft that resulted in significant improvement of the same.
9. IANA Considerations
This document places no requests to IANA.
10.
References
10.1 Normative References
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998
[ISO] "Intermediate system to Intermediate system routeing
information exchange protocol for use in conjunction with
the Protocol for providing the Connectionless-mode
Network Service (ISO 8473) ", ISO/IEC 10589:1992
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2453] Malkin, G., "RIP Version 2", RFC 2453, November 1998
[RFC4822] R. Atkinson and M. Fanto, "RIPv2 Cryptographic
Authentication", RFC 4822, February 2007
[RFC5304] Li, T. and R. Atkinson, "Intermediate System to
Intermediate System (IS-IS) Cryptographic
Authentication", RFC 5304, October 2008
[RFC5340] Coltun, R., et. al, "OSPF for IPv6", RFC 5340, July
2008.
[RFC4835] Manral, V., "Cryptographic Algorithm Implementation
Requirements for Encapsulating Security Payload (ESP) and
Authentication Header (AH)", RFC 4835, April 2007
[RFC2080] Malkin, G. and Minnear, R., "RIPng for IPv6", RFC 2080,
January 1997
[RFC5310] Bhatia, M., et. al., "IS-IS Generic
Cryptographic Authentication", RFC 5310, February 2009
[RFC5709] Bhatia, M., Manral, V., et al., "OSPF HMAC-SHA
Bhatia and Manral [Page 9]
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Cryptographic Authentication", RFC 5709, October 2009
10.2
Informative References
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC
1321, April 1992
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December
2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, December 2005.
[RFC4522] Gupta, M. and Melam, N.,"Authentication/Confidentiality
for OSPFv3", RFC 4522, June 2006
[RFC1388] Malkin, G., "RIP Version 2 Carrying Additional
Information", RFC 1388, January 1993.
[RFC1723] Malkin, G., "RIP Version 2 - Carrying Additional
Information", STD 56, RFC 1723, November 1994.
[RFC2082] Baker, F. and Atkinson, R., "RIP-2 MD5
Authentication", RFC 2082, January 1997
[SHS] National Institute of Standards and Technology (NIST),
FIPS Publication 180-3: Secure Hash Standard, October
2008.
Author's Addresses
Manav Bhatia
Alcatel-Lucent
Bangalore, India
Email: manav.bhatia@alcatel-lucent.com
Vishwas Manral
IP Infusion
Almora, Uttarakhand
India
Email: vishwas@ipinfusion.com
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