One document matched: draft-zheng-mpls-ldp-hello-crypto-auth-01.txt
Differences from draft-zheng-mpls-ldp-hello-crypto-auth-00.txt
Network working group L. Zheng
Internet Draft M. Chen
Intended status: Standards Track Huawei Technologies
Updates: RFC 5036 (if approved)
Expires: September 2011 March 14, 2011
LDP Hello Cryptographic Authentication
draft-zheng-mpls-ldp-hello-crypto-auth-01.txt
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Abstract
This document introduces a new Cryptographic Authentication TLV
which is used in LDP Hello message as an optional parameter. It
enhances the authentication mechanism for LDP by securing the Hello
message against spoofing attack.
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. Cryptographic Authentication TLV .............................. 4
2.1. Optional Parameter for Hello Message ..................... 4
2.2. Cryptographic Authentication TLV Encoding ................ 4
3. Cryptographic Aspects ......................................... 5
3.1. Cryptographic Key ........................................ 6
3.2. Hash ..................................................... 6
3.3. Result ................................................... 7
4. Processing Hello Message Using Cryptographic Authentication ... 7
4.1. Transmission Using Cryptographic Authentication .......... 7
4.2. Receipt Using Cryptographic Authentication ............... 7
5. Security Considerations ....................................... 8
6. IANA Considerations ........................................... 8
7. Acknowledgments ............................................... 9
8. References .................................................... 9
8.1. Normative References ..................................... 9
8.2. Informative References .................................. 9
Authors' Addresses .............................................. 10
1. Introduction
The Label Distribution Protocol (LDP) [RFC 5036] utilizes LDP
sessions that run between LDP peers. The peers may be directly
connected at the link level or may be remote. A label switching
router (LSR) that speaks LDP may be configured with the identity of
its peers or may discover them using the LDP Hello message sent
encapsulated in UDP that may be addressed to "all routers on this
subnet" or to a specific IP address. Periodic Hello messages are
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also used to maintain the relationship between LDP peers necessary
to keep the LDP session active.
Unlike all other LDP messages, the Hello messages are sent using UDP
not TCP. This means that they cannot benefit from the security
mechanisms available with TCP. [RFC5036] does not provide any
security mechanisms for use with Hello messages except to note that
some configuration may help protect against bogus discovery events.
Spoofing a Hello packet for an existing adjacency can cause the
valid adjacency to time out and in turn can result in termination of
the associated session. This can occur when the spoofed Hello
specifies a smaller Hold Time, causing the receiver to expect Hellos
within this smaller interval, while the true neighbor continues
sending Hellos at the previously agreed lower frequency. Spoofing a
Hello packet can also cause the LDP session to be terminated
directly, which can occur when the spoofed Hello specifies a
different Transport Address, other than the previously agreed one
between neighbors. Spoofed Hello messages is observed and reported
as real problem in production networks.
As described in [RFC5036], the threat of spoofed Basic Hellos can be
reduced by accepting Basic Hellos only on interfaces to which LSRs
that can be trusted, and ignoring Basic Hellos not addressed to the
"all routers on this subnet" multicast group. Spoofing attacks via
Extended Hellos are potentially more serious threat. An LSR can
reduce the threat of spoofed Extended Hellos by filtering them and
accepting only those originating at sources permitted by an access
list. However, performing the filtering using access lists requires
LSR resource, and the LSR is still vulnerable to the IP source
address spoofing.
This document introduces a new Cryptographic Authentication TLV
which is used in LDP Hello message as an optional parameter. It
enhances the authentication mechanism for LDP by securing the Hello
message against spoofing attack, and an LSR can be configured to
only accept Hello messages from specific peers when authentication
is in use.
Using this Cryptographic Authentication TLV, one or more secret keys
(with corresponding key IDs) are configured in each system. For each
LDP Hello packet, the key is used to generate and verify a HMAC Hash
that is stored in the LDP Hello packet. For cryptographic hash
function, this document proposes to use SHA-1, SHA-256, SHA-384, and
SHA-512 defined in US NIST Secure Hash Standard (SHS) [FIPS-180-3].
The HMAC authentication mode defined in NIST FIPS 198 is used [FIPS-
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198]. Of the above, implementations MUST include support for at
least HMAC-SHA-256 and SHOULD include support for HMAC-SHA-1 and MAY
include support for either of HMAC-SHA-384 or HMAC-SHA-512.
2. Cryptographic Authentication TLV
2.1. Optional Parameter for Hello Message
[RFC5036] defines the encoding for the Hello message. Each Hello
message contains zero or more Optional Parameters, each encoded as a
TLV. Three Optional Parameters are defined by [RFC5036]. This
document defines a new Optional Parameter: the Cryptographic
Authentication parameter.
Optional Parameter Type
------------------------------- --------
IPv4 Transport Address 0x0401 (RFC5036)
Configuration Sequence Number 0x0402 (RFC5036)
IPv6 Transport Address 0x0403 (RFC5036)
Cryptographic Authentication 0x0404 (this document, TBD by
IANA)
The Cryptographic Authentication TLV Encoding is described in
section 2.2.
2.2. Cryptographic Authentication TLV Encoding
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Auth (0x0404) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth Type | Reserved | Auth Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Authentication Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Type: 0x0404 (TBD by IANA), Cryptographic Authentication
- Length: Specifying the length in octets of the value field.
- Auth Type: The authentication type in use
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0 - HMAC-SHA-1
1 - HMAC-SHA-256
2 - HMAC-SHA-384
3 - HMAC-SHA-512
4-255 - Reserved for future use
(TBD by IANA)
- Reserved: MUST be set to zero on transmit, and ignored on receipt
- Auth Key ID: The authentication key ID in use for this packet.
This allows one or more keys to be active simultaneously.
- Authentication Data:
This field carries the digest computed by the Cryptographic
Authentication algorithm in use. The length of the Authentication
Data varies based on the cryptographic algorithm in used, which is
shown as below:
Auth type Length
---------------------- ----------
HMAC-SHA1 20 bytes
HMAC-SHA-256 32 bytes
HMAC-SHA-384 48 bytes
HMAC-SHA-512 64 bytes
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 specified by Auth Type (e.g.
SHA-256).
- K is the Authentication Key for the Hello packet.
- Ko is the cryptographic key used with the hash algorithm.
- B is the block size of H, in octets.
For SHA-1 and SHA-256: B == 64
For SHA-384 and SHA-512: B == 128
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- L is the length of the hash outputs, in octets.
- XOR is the exclusive-or operation.
- Ipad is the byte 0x36 repeated B times.
- Opad is the byte 0x5c repeated B times.
- Apad is the byte 0x878FE1F3 repeated (L/4) times.
3.1. Cryptographic Key
As described in RFC 2104, the authentication key K can be of any
length up to B. Applications that use keys longer than B bytes will
first hash the key using H and then use the resultant L byte string
as the actual key to HMAC.
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 trailing
zeros such that Ko is L octets long.
3.2. Hash
First, the Authentication Data field in the Cryptographic
Authentication TLV is filled with the value Apad and the Auth Type
field is set accordingly per Cryptographic Authentication algorithm
in use.
Then, to compute HMAC over the Hello packet it performs:
H(Ko XOR Opad || H(Ko XOR Ipad || (Hello Packet)))
Hello Packet here is the entire LDP Hello packet including the IP
header.
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3.3. Result
The resultant Hash becomes the Authentication Data that is
sent in the Authentication Data field of the Cryptographic
Authentication TLV. The length of the Authentication Data field is
always identical to the message digest size of the specific hash
function H that is being used.
4. Processing Hello Message Using Cryptographic Authentication
4.1. Transmission Using Cryptographic Authentication
Prior to transmitting Hello message, the Auth Type field is set to
indicate the authentication type in use. The Length in the
Cryptographic Authentication TLV header is set as per the
authentication algorithm that is being used. It is set to 24 for
HMAC-SHA-1, 36 for HMAC-SHA-256, 52 for HMAC-SHA-384 and 68 for
HMAC-SHA-512.
The Auth Key ID field is set to the ID of the current authentication
key. The HMAC Hash is computed as explained in Section 3. The
resulting Hash is stored in the Authentication Data field prior to
transmission. The authentication key MUST NOT be carried in the
packet.
4.2. Receipt Using Cryptographic Authentication
The receiving LSR applies acceptability criteria for received Hellos
using cryptographic authentication. If the Cryptographic
Authentication TLV is unknown to the receiving LSR, the received
packet MUST be discarded according to Section 3.5.1.2.2 of [RFC5036].
If the Cryptographic Authentication TLV in a received Hello packet
does not contain a known and acceptable Auth Type value, then the
received packet MUST be discarded. If the Auth Key ID field does not
match the ID of a configured authentication key, the received packet
MUST be discarded.
Before the receiving LSR performs any processing, it needs to save
the values of the Authentication Data field. The receiving LSR then
replaces the contents of the Authentication Data field with Apad,
computes the Hash, using the authentication key specified by the
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received Auth Key ID field, as explained in Section 3. If the
locally computed Hash is equal to the received value of the
Authentication Data field, the received packet is accepted for other
normal checks and processing as described in [RFC5036]. Otherwise,
the received packet MUST be discarded.
5. Security Considerations
Section 1 of this document describes the security issues arising
from the use of unsecured LDP Hello messages. In order to combat
those issues, it is RECOMMENDED that all deployments use the
Cryptographic Authentication TLV to secure the Hello message.
The quality of the security provided by the Cryptographic
Authentication TLV depends completely on the strength of the
cryptographic algorithm in use, the strength of the key being used,
and the correct implementation of the security mechanism in
communicating LDP implementations. Also, the level of security
provided by the Cryptographic Authentication TLV varies based on the
authentication type used.
6. IANA Considerations
IANA maintains a registry of LDP message parameters with a sub-
registry to track LDP TLV Types. This document request IANA to
assign a new TLV Types as follows:
TLV Type
Cryptographic Authentication 0x0404 (TBD)
This document also request IANA to assign a new registry titled "LDP
Hello Authentication Type", its recommended values as follows:
Value LDP Hello Authentication Type Name
------- -----------------------------------
0 HMAC-SHA1
1 HMAC-SHA-256
2 HMAC-SHA-384
3 HMAC-SHA-512
4-255 Unassigned
(TBD)
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7. Acknowledgments
The authors would like to thank Liu Xuehu for his work on background
and motivation for LDP Hello authentication. The authors also would
like to thank Adrian Farrel, Thomas Nadeau, So Ning, Eric Rosen, Sam
Hartman and Manav Bhatia for their valuable comments.
8. References
8.1. Normative References
[RFC2104] Krawczyk, H. et al., "HMAC: Keyed-Hashing for Message
Authentication", RFC 2104, February 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[FIPS-180-3] National Institute of Standards and 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
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC 2385, August 1998.
[RFC4634] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and HMAC-SHA)", RFC 4634, July 2006.
[RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
Authentication", RFC 5709, October 2009.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection",
RFC 5880, June 2010.
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Authors' Addresses
Lianshu Zheng
Huawei Technologies Co., Ltd.
Huawei Building, No.3 Xinxi Road,
Hai-Dian District,
Beijing 100085
China
Email: verozheng@huawei.com
Mach(Guoyi) Chen
Huawei Technologies Co., Ltd.
Huawei Building, No.3 Xinxi Road,
Hai-Dian District,
Beijing 100085
China
Email: mach@huawei.com
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