Internet DRAFT - draft-bhatia-manral-crypto-req-ospf
draft-bhatia-manral-crypto-req-ospf
Internet Draft February 2007
Network Working Group Manav Bhatia
Internet Draft Alcatel-Lucent
Expires: August 2007 Vishwas Manral
IP Infusion
Cryptographic Algorithm Implementation Requirements for OSPF
draft-bhatia-manral-crypto-req-ospf-01.txt
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Abstract
OSPF defines three different kinds of authentication schemes: Null
authentication, simple password and cryptographic authentication. The
cryptographic authentication scheme can make use of various
cryptographic algorithms in order to authenticate the OSPF packets.
To ensure interoperability between disparate implementations, it is
necessary to specify a set of mandatory-to-implement algorithms to
ensure that there is at least one algorithm that all implementations
will have available.
This document defines the current set of mandatory-to-implement
algorithms to be used for the cryptographic authentication for OSPF
as well as specifying the algorithms that should be implemented
because they may be promoted to mandatory at some future time.
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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 [KEYWORDS]
1. Introduction
OSPF as defined in [RFC 2328] includes three different types of
authentication schemes: Null authentication, simple password and
cryptographic authentication. NULL authentication is akin to having
no authentication at all. In the simple password scheme of
authentication, the passwords are exchanged in the cleartext on the
network and anyone with physical access to the network can learn the
password and compromise the security of the OSPF domain.
In the cryptographic authentication scheme, the OSPF routers on a
common network/subnet share a secret key which is used to generate a
keyed MD5 digest for each packet and a monotonically increasing
sequence number scheme is used to prevent replay attacks.
This isn't good enough as there have recently been reports about
attacks on the collision resistance properties of MD5 [MD5-attack]
and SHA-1 [SHA-1-attack] hash functions. MD5CRK, was a distributed
computing project to break the MD5 hash algorithm in a short period
of time. The project closed down with the publication of the paper
[MD5-attack].
It was discovered that collisions can be found in MD5 algorithm in
less than 24 hours, making MD5 very insecure. Further research has
verified this result and shown other ways to find collisions in MD5
hashes. We thus need to move away from MD5 towards more complex and
difficult to break hash algorithms.
The [OSPF-HMAC] document recently submitted in the IETF addresses
this. It is imperative that we move away from using Keyed MD5 to
something that’s cryptographically more stronger (like HMAC-SHA-1).
However, the nature of cryptography is that new algorithms surface
continuously and existing algorithms are continuously attacked. An
algorithm believed to be strong today may be demonstrated to be weak
tomorrow. Given this, the choice of mandatory-to-implement algorithm
should be conservative so as to minimize the likelihood of it being
compromised quickly.
Also, we need to recognize that the mandatory-to-implement
algorithm(s) may need to change over time to adapt to the changing
world. For this reason, the selection of mandatory-to-implement
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algorithms should not be included in the base OSPF specification.
This way it is only this document that needs to get updated, whenever
there is a need to update the status of mandatory-to-implement
authentication algorithms.
2. Requirements Terminology
Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and
"MAY" that appear in this document are to be interpreted as described
in [RFC2119].
We define some additional terms here:
SHOULD+ This term means the same as SHOULD. However, it is
likely that an algorithm marked as SHOULD+ will be
promoted at some future time to be a MUST.
SHOULD- This term means the same as SHOULD. However, it is
likely that an algorithm marked as SHOULD- will be
deprecated to a MAY or worse in a future version of
this document.
MUST- This term means the same as MUST. However, we expect
that at some point in the future this algorithm will no
longer be a MUST.
3. Authentication Scheme Selection
For OSPF implementations to interoperate, they must support one or
more authentication schemes in common. This section specifies the
requirements for standards conformant OSPF implementations, which
desire to utilize the security feature.
Old Old New
Req. RFC Requirement Authentication Scheme
--- ------ ----------- ------------------------
MUST 2328 SHOULD NOT Null Authentication (1)
MUST 2328 SHOULD NOT Simple Password (2)
MUST 2328 MUST Cryptographic Authentication
The above is only true in case security is required, if there is no
requirement of security from an implementation, the above
requirements need not be followed
Notes:
(1)This is used when no authentication is required as there are
scenarios when the operator does not really require any sort of
authentication. However, this document lists down the requirements
that an implementation must support in order to authenticate the
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OSPF packets. Clearly, NULL should not be used for that if the
operator has network security in mind.
(2)This is used when all the routers can “trust” one another but the
operator does not want an accidental introduction of a router in
the domain. Again the same logic applies. This scheme of
authentication is useful, but not when the operator wants to
“cryptographically” authenticate the OSPF packets.
4. Authentication Algorithm Selection
For OSPF implementations to interoperate, they must support one or
more authentication algorithms in common that can be used in the
cryptographic scheme of authentication.
This section details the authentication algorithm requirements for
standards conformant OSPF implementations.
Old Old New
Req. RFC Requirement Authentication Algorithm
--- ------ ----------- ------------------------
MUST 2328 MUST- Keyed MD5
- - SHOULD+ HMAC-SHA-1 [OSPF-HMAC]
- - MAY+ HMAC-SHA-256/HMAC-SHA-384/HMAC-SHA-512
5. Security Considerations
The cryptographic mechanisms defined in this document define only
authentication algorithms, and do not provide any confidentiality.
However encrypting the content of the packet (providing
confidentiality) is not of as great a value to routing protocols as
authenticating the source of the packet.
It should be noted that 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.
To ensure greater security, the keys used must be changed
periodically and implementations MUST be able to store and use more
than one key at the same time.
This document concerns itself with the selection of cryptographic
algorithms for the use of OSPF, specifically with the selection of
"mandatory-to-implement" algorithms. The algorithms identified in
this document as "MUST implement" or "SHOULD implement" are not known
to be broken at the current time, and cryptographic research so far
leads us to believe that they will likely remain secure into the
foreseeable future. However, this isn't necessarily forever. We
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would therefore expect that new revisions of this document will be
issued from time to time that reflect the current best practice in
this area.
6. Acknowledgements
Much of the wording herein was adapted from RFC 4307, "Cryptographic
Algorithms for Use in the Internet Key Exchange Version 2", by
Jeffrey I. Schiller.
7. IANA Considerations
This document places no requests to IANA.
8. References
8.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119
[RFC2328] Moy, J., "OSPF Version 2", RFC 2328, April 1998
[OSPF-HMAC] Bhatia, M., Manral, V. and White, R.," OSPF HMAC
Cryptographic Authentication”, Work in Progress
8.2 Informative References
[MD5-attack] Wang, X. et al., "Collisions for Hash Functions MD4,
MD5, HAVAL-128 and RIPEMD", August 2004,
http://eprint.iacr.org/2004/199
[SHA-1-attack] Wang, X. et al., "Collision Search Attacks on SHA1",
February 2005,
http://theory.csail.mit.edu/~yiqun/shanote.pdf
9. Author's Addresses
Manav Bhatia
Alcatel-Lucent
Bangalore, India
Email: manav@alcatel-lucent.com
Vishwas Manral
IP Infusion
Almora, Uttarakhand
India
Email: vishwas@ipinfusion.com
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