Internet Draft draft-bhatia-manral-crypto-req-isis-01.txt March 2007
Network Working Group Manav Bhatia
Internet Draft Alcatel-Lucent
Expires: September 2007 Vishwas Manral
IP Infusion
Cryptographic Algorithm Implementation Requirements for IS-IS
draft-bhatia-manral-crypto-req-isis-01.txt
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Abstract
IS-IS currently defines two different kinds of authentication
schemes: Clear Text password and HMAC-MD5. There has been recently a
new draft submitted that adds support for a generic cryptographic
authentication scheme, which can make use of different cryptographic
algorithms in order to authenticate the IS-IS PDUs.
To ensure interoperability between disparate implementations, it is
imperative that we 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 IS-IS
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as well as specifying the algorithms that should be implemented
because they may be promoted to mandatory at some future time.
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
IS-IS [ISO] [RFC1195] specification allows for authentication of its
PDUs via the authentication TLV 10 that is carried as the part of the
PDU. The base spec has provision for only clear text passwords and
RFC 3567 [RFC3567] augments this to provide the capability to use
HMAC-MD5 authentication for its PDUs.
In the clear text password scheme of authentication, the passwords
are exchanged in the clear text on the network and anyone with
physical access to the network can learn the password and compromise
the security of the IS-IS domain.
The HMAC-MD5 scheme is also not good enough as there have recently
been reports about attacks on the collision resistance properties of
MD5 [MD5-attack]. 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 [ISIS-HMAC] document recently submitted in the IETF addresses
this. It is imperative that we move away from using 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
algorithms should not be included in the base IS-IS specification.
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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 IS-IS implementations to interoperate, they must support one or
more authentication schemes in common. This section specifies the
requirements for standards conformant IS-IS implementations, which
desire to utilize the security feature.
Old Old New
Req. RFC Requirement Authentication Scheme
--- ------ ----------- ------------------------
MUST ISO-10589/ SHOULD NOT Clear Text Password (1)
RFC 1195
MUST 3567 MUST- HMAC-MD5
- - SHOULD+ Cryptographic Auth [ISIS-HMAC]
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 all the routers can "trust" one another but the
operator does not want an accidental introduction of a router in
the domain. This scheme of authentication is useful, but not when
the operator wants to "cryptographically" authenticate the OSPF
packets.
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4. Authentication Algorithm Selection
For IS-IS 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 IS-IS implementations.
Old Old New
Req. RFC Requirement Authentication Algorithm
--- ------ ----------- ------------------------
MUST 3567 MUST- HMAC-MD5
- - SHOULD+ HMAC-SHA-1 [ISIS-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 IS-IS, 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
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
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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
[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.
[RFC3567] Li, T. and R. Atkinson, "Intermediate System to
Intermediate System (IS-IS) Cryptographic
Authentication", RFC 3567, July 2003
[ISIS-HMAC] Bhatia, M., Manral, V. and White, R.,"ISIS 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
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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