One document matched: draft-bhatia-ipsecme-esp-null-00.txt
Internet Draft Identifying ESP-NULL Packets December 2008
Network Working Group Manav Bhatia
Internet Draft Alcatel-Lucent
Intended Status: Proposed Standard
Expires: May 2009
Identifying ESP-NULL Packets
draft-bhatia-ipsecme-esp-null-00.txt
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Abstract
Encapsulating Security Payload (ESP) [RFC4303] provides data
integrity protection, confidentiality and data origin authentication
for data transported in an IP packet.
There are various applications and protocols that do not require
confidentiality but only need data integrity assurance or data origin
authentication. Since ESP support is mandatory for IPSec, such
applications end up using ESP with NULL encryption.
However, because of the way ESP is defined, it is impossible for
firewalls and intermediate routers to differentiate between encrypted
ESP and ESP NULL packets by simply examining them. This poses
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problems for the firewalls since such packets cannot be filtered and
identified. It poses a different set of problems for routers since
such packets cannot be properly filtered, classified and prioritized.
This document proposes an extension to ESP so that firewalls and
routers can disambiguate between ESP encrypted and ESP NULL encrypted
packets.
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 [RFC2119].
1. Introduction
ESP-NULL is used when confidentiality is not required and only source
authentication and data integrity assurance is desired.
IPSec mandates the use of ESP while keeps support for Authentication
Header (AH) [RFC4302] as optional. Thus, new protocols using IPSec
for data integrity also mandate the use of ESP-NULL. It is also
mandatory [RFC4835] for all ESP implementations to provide support
for ESP NULL encryption. Because of these factors a lot of vendors do
not implement AH and only support ESP-NULL for data integrity and
source authentication. The traffic using ESP-NULL is thus only going
to increase with time.
Firewalls and intermediate routers in the network find it impossible
to parse ESP packets since they have no idea whether the packet is
encrypted or not. They cannot for this reason implement filters and
access control lists (ACLs).
ACLs are highly desirable and used extensively by service providers
to block undesired traffic coming from other domains.
This draft therefore proposes an extension to ESP with which
identifying an ESP-NULL packet from an ESP encrypted packet becomes
trivial. It is backward compatible, therefore devices that do not
understand this extension would treat packets using this extension as
normal ESP packets.
The extension described in this draft is applicable for both the
tunnel and the transport modes of ESP.
2. Explicitly Marking ESP NULL Packets
ESP-NULL packets, for both implementations based on [RFC2410] and
[RFC4543] MUST be sent with a well known, reserved SPI of 1. The
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Internet Draft Identifying ESP-NULL Packets December 2008
original SPI should be included as part of the payload. This is
encoded in the first 4 octets of the payload section of the ESP
header. An implementation MUST put the next-header and the ESP header
th th
length as the 4 and the 5 octets of the payload.
Since the packet is not encrypted these fields would be sent in clear
text and would be visible to all.
An extended ESP packet using NULL encryption would thus look like
this:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved Security Parameters Index (RSPI) = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original Security Parameters Index (SPI) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| next-header | eESP HDRLen | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Payload Data* (variable) |
~ ~
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Padding (0-255 bytes) |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Pad Length | Next Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication Data (variable) |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
Reserved Security Parameters Index (RSPI): Well known value that
should be given by IANA to indicate that it is an ESP-NULL packet.
next-header: This is a one octet field that indicates the next
protocol header. Explicitly mentioning this provides an easy access
to a HW parser to extract the upper layer protocol.
eESP HDRLen: This is a one octet field that gives the length of the
extended ESP header + IV (if mandated by the authentication
algorithm). It is an offset to the beginning of the payload data.
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Intermediate nodes (routers, firewalls, etc) interested in inspecting
the packets en route can look at the SPI value at the start of the
ESP header. If there are unaware of this extension then this packet
would appear like a normal ESP packet. However, compliant
implementations will understand that this is an extended ESP packet
and would have enough information to be able to deep inspect the ESP-
NULL packet.
The compliant end nodes (routers) can similarly parse the packet
easily. If the SPI value is 1, then it can extract the original SPI
from the payload and process the packet accordingly.
3. Authenticating the Packets
All fields of the extended ESP header starting with the RSPI and
ending with the Next Header in the ESP trailer are included in the
ESP data integrity check.
The authentication data field is used to hold the result of the data
integrity check done on the ESP packet. The length of this field
depends on the authentication algorithm employed by the Security
Association (SA) used to process this packet.
4. Acknowledgements
The author would like to thank Jack Kohn for his useful comments.
5. IANA Considerations
IANA must assign a value that for Reserved SPI which will be used as
described above. The draft uses a value 1 to foster pre-standard
implementations.
6. Security Considerations
This proposal neither increases nor decreases the security for ESP.
All considerations valid for ESP also apply here.
7. References
7.1 Normative References
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, February 2001.
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[RFC2410] Glenn, R., and Kent, S., "The NULL Encryption Algorithm and
its Use With IPsec", RFC 2410, November 1998.
[RFC4543] McGrew, D. and Viega, J., "The Use of Galois Message
Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543,
May 2006.
7.2 Informative References
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC4835] Manral, V., "Cryptographic Algorithm Implementation
Requirements for Encapsulating Security Payload (ESP) and
Authentication Header (AH)", RFC 4835, APRIL 2007.
8. Author's Addresses
Manav Bhatia
Alcatel-Lucent,
Bangalore, India
Email: manav@alcatel-lucent.com
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Internet Draft Identifying ESP-NULL Packets December 2008
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