Network Working Group E. Ertekin
Internet-Draft J. Pezeshki
Expires: February 16, 2009 M. Casey
C. Christou
Booz Allen Hamilton
C. Bormann
Universitaet Bremen TZI
August 15, 2008
IPsec Extensions to Support Robust Header Compression over IPsec
(RoHCoIPsec)
draft-ietf-rohc-ipsec-extensions-hcoipsec-02
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Abstract
Integrating RoHC with IPsec (RoHCoIPsec) offers the combined benefits
of IP security services and efficient bandwidth utilization.
However, extensions to the SPD and SAD are required in order to
integrate RoHC with IPsec. This document describes the IPsec
extensions required to support RoHCoIPsec.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Extensions to IPsec Databases . . . . . . . . . . . . . . . . 3
2.1. Security Policy Database (SPD) . . . . . . . . . . . . . . 3
2.2. Security Association Database (SAD) . . . . . . . . . . . 4
3. Extensions to IPsec Processing . . . . . . . . . . . . . . . . 5
3.1. Addition to the IANA Protocol Numbers Registry . . . . . . 5
3.2. Verifying the Integrity of Decompressed Packet Headers . . 5
3.2.1. ICV Computation and Integrity Verification . . . . . . 6
3.3. Nested IPComp and RoHCoIPsec Processing . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
Using IPsec ([IPSEC]) protection offers various security services for
IP traffic. However, these benefits come at the cost of additional
packet headers, which increase packet overhead. As described in
[ROHCOIPSEC], Robust Header Compression (RoHC [ROHC]) can be used
with IPsec to reduce the overhead associated with IPsec-protected
packets.
IPsec-protected traffic is carried over Security Associations (SAs),
whose parameters are negotiated on a case-by-case basis. The
Security Policy Database (SPD) specifies the services that are to be
offered to IP datagrams, and the parameters associated with SAs that
have been established are stored in the Security Association Database
(SAD). To integrate RoHC and IPsec, various extensions to the SPD
and SAD that incorporate RoHC-relevant parameters are required.
In addition, three extensions to IPsec processing are required.
First, a mechanism for identifying RoHC packets must be defined.
Second, a mechanism is required to ensure the integrity of the
decompressed packet. Finally, the order of the inbound and outbound
processing must be enumerated when nesting IP Compression (IPComp
[IPCOMP]), RoHC, and IPsec processing.
2. Extensions to IPsec Databases
The following subsections specify extensions to the SPD and the SAD
to support RoHCoIPsec.
2.1. Security Policy Database (SPD)
In general, the SPD is responsible for specifying the security
services that are offered to IP datagrams. Entries in the SPD
specify how to derive the corresponding values for SAD entries. To
support RoHC, the SPD must be extended to include per-channel RoHC
parameters. Together, the existing IPsec SPD parameters and the RoHC
parameters will dictate the services that are provided to packets
protected by IPsec.
The fields contained within each SPD entry are defined in [IPSEC],
Section 4.4.1.2. To support RoHC, several processing info fields
must be added to the SPD; these fields contain information regarding
the RoHC profiles and channel parameters supported by the local RoHC
instance.
The SPD specifies what services are to be offered to IP datagrams,
and in what fashion. To offer IP datagrams compression services, the
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per-channel configuration parameters, defined in [ROHC], are added to
the SPD. Specifically, the following parameters must be included if
the processing info field in the SPD is set to PROTECT (suggested
values for these parameters are consistent with [ROHCPPP]):
MAX_CID: The highest context ID number to be used by the
compressor. MAX_CID must be at least 0 and at most 16383 (The
value 0 implies having one context). The suggested value for
MAX_CID is 15.
PROFILES: This indicates the RoHC profiles supported by the
decompressor. The list of possible values this field may assume
is defined in the [ROHCPROF] registry.
MRRU: The size of the largest reconstructed unit that the
decompressor is expected to reassemble from segments. In general,
it is not anticipated that a RoHCoIPsec instance will use RoHC
segmentation. Consequently, the suggested value for MRRU is 0.
MAX_HEADER: The largest header size (in octets) that can be
compressed. Note that the four RoHC profiles defined in RFC 3095
do not provide for a MAX_HEADER parameter. The parameter
MAX_HEADER is therefore without consequence in these profiles.
Other profiles (e.g., ones based on RFC 2507) can make use of the
parameter by explicitly referencing it.
Note: The RoHC LARGE_CIDS channel parameter is set implicitly, based
on the value of MAX_CID. Furthermore, if a SA in the reverse
direction exists, the RoHC FEEDBACK_FOR channel parameter is set
implicitly to the RoHC channel associated with the SA in the reverse
direction. If a SA in the reverse direction does not exist, RoHC
must operate in the Unidirectional Mode. Because both of these RoHC
channel parameters are set implicitly, they are not stored in the
SPD.
In addition to these RoHC channel parameters, a field within the SPD
entry is required to store a list of integrity algorithms supported
by the RoHCoIPsec instance. This integrity algorithm will be used by
the RoHC process to ensure that packet headers are properly
decompressed (see Section 3.2).
2.2. Security Association Database (SAD)
Each entry within the SAD defines the parameters associated with each
established SA. Unless if the "populate from packet" (PFP) flag is
asserted for a particular field, SAD entries are determined by the
corresponding SPD entries during the creation of the SA.
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The data items contained within the SAD are defined in [IPSEC],
Section 4.4.2.1. To support RoHC, this list of data items is
augmented to include a "RoHC Data Item" field that defines the RoHC
parameters. These parameters (i.e., MAX_CID, PROFILES, MRRU, and
MAX_HEADER) are enumerated above in Section 2.1. In addition, the
FEEDBACK_FOR parameter is also included, which is associated with the
SA in the reverse direction (this data item does not need to be
included in the SPD, since its value is implicitly derived).
Finally, two additional data items are required to store the
Integrity Algorithm and respective key that is to be used to ensure
that packets are properly decompressed (see Section 3.2).
These "RoHC Data Item" values may be initialized manually (i.e.,
administratively configured for manual SAs), or initialized via a key
exchange protocol (e.g. IKEv2 [IKEV2]) that has been extended to
support the negotiation of RoHC parameters [IKEV2EXT].
3. Extensions to IPsec Processing
3.1. Addition to the IANA Protocol Numbers Registry
In order to demultiplex header-compressed from uncompressed traffic
on a RoHC-enabled SA, a "RoHC" value must be reserved in the IANA
Protocol Numbers registry. If an outbound packet has a compressed
header, the Next Header field of the security protocol header (e.g.,
AH [AH], ESP [ESP]) must be set to the "RoHC" protocol identifer. If
the packet header has not been compressed, the Next Header field
remains unaltered. Conversely, for an inbound packet, the value of
the security protocol Next Header field is checked to determine if
the packet includes a RoHC header.
3.2. Verifying the Integrity of Decompressed Packet Headers
Since RoHC is inherently a lossy algorithm, RoHCoIPsec will use an
additional Integrity Algorithm (and respective key) to compute a
second Integrity Check Value (ICV) for the uncompressed packet.
Specifically, this ICV will be computed for the uncompressed IP
header, as well at the higher-layer headers and the packet payload.
This ICV will be appended to the RoHC-compressed packet. At the
decompressor, the decompressed packet (including the uncompressed IP
header, higher-layer headers, and packet payload; but not including
the authentication data) will be used with the Integrity Algorithm
(and its respective key) to compute a value that will be compared to
the ICV. If these values are not identical, the decompressed packet
must be dropped by the decompressor.
Figure 1 illustrates the composition of a RoHCoIPsec-processed IPv4
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packet. In the example, TCP/IP compression is applied, and the
packet is processed with tunnel mode ESP.
BEFORE COMPRESSION AND APPLICATION OF ESP
----------------------------
IPv4 |orig IP hdr | | |
|(any options)| TCP | Data |
----------------------------
AFTER ROHCOIPSEC COMPRESSION AND APPLICATION OF ESP
------------------------------------------------------
IPv4 | new IP hdr | | Cmpr | | RoHC | ESP | ESP|
|(any options)| ESP | Hdr. |Data| ICV |Trailer| ICV|
------------------------------------------------------
Figure 1. Example of a RoHCoIPsec-processed packet.
Note: The authentication data should never be included in the
calculation of the ICV.
3.2.1. ICV Computation and Integrity Verification
In order to correctly verify the integrity of the decompressed
packets, the processing steps for RoHCoIPsec must be implemented in a
specific order, as given below.
For outbound packets that are to be processed by RoHC:
o An ICV is computed for the uncompressed packet via RoHCoIPsec's
Integrity Algorithm (and respective key)
o The packet is compressed by the RoHC process
o The ICV is appended to the end of the compressed packet
o The security protocol is applied to the packet
For inbound packets that are to be decompressed by RoHC:
o A packet received on a RoHC-enabled SA is IPsec-processed
o The packet is decompressed by the RoHC process
o The decompressed packet is used with the Integrity Algorithm (and
its respective key) to compute a value that is compared to the ICV
(if these two values differ, the packet is dropped)
3.3. Nested IPComp and RoHCoIPsec Processing
IPComp ([IPCOMP]) is another mechanism that can be implemented to
reduce the size of an IP datagram. If IPComp and RoHCoIPsec are
implemented in a nested fashion, the order of the outbound and
inbound processing steps must be carefully enumerated.
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For outbound packets that are to be processed by IPcomp and RoHC:
o The ICV is computed for the uncompressed packet, and the
appropriate RoHC compression profile is applied to the packet
o IPComp is applied, and the packet is sent to the IPsec process
o The security protocol is applied to the packet
Conversely, for inbound packets that are to be both RoHC- and IPcomp-
decompressed:
o A packet received on a RoHC-enabled SA is IPsec-processed
o The datagram is decompressed based on the appropriate IPComp
algorithm
o The packet is sent to the RoHC module for header decompression and
integrity verification
4. Security Considerations
A RoHCoIPsec implementer should consider the strength of protection
provided by the integrity check algorithm used to verify the valid
decompression of RoHC-compressed packets. Failure to implement a
strong integrity check algorithm increases the probability of an
invalidly decompressed packet to be forwarded by a RoHCoIPsec device
into a protected domain. In general, if an integrity check algorithm
is used with IPsec, it is recommended that the integrity check
algorithm used by RoHC is at least the same strength.
The implementation of RoHCoIPsec may increase the susceptibility for
traffic flow analysis, where an attacker can identify new traffic
flows by monitoring the relative size of the encrypted packets (i.e.
a group of "long" packets, followed by a long series of "short"
packets may indicate a new flow for some RoHCoIPsec implementations).
To mitigate this concern, RoHC padding mechanisms may be used to
arbitrarily add padding to transmitted packets to randomize packet
sizes.
5. IANA Considerations
IANA is requested to allocate one value within the "Protocol Numbers"
registry [PROTOCOL] for "RoHC". This value will be used to indicate
that the next level protocol header is a RoHC header.
6. Acknowledgments
The authors would like to thank Mr. Sean O'Keeffe, Mr. James Kohler,
Ms. Linda Noone of the Department of Defense, and Mr. A. Rich Espy of
OPnet for their contributions and support for developing this
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document. In addition, the authors would like to thank Mr. Rohan
Jasani for his valuable assistance. Finally, the authors would like
to thank the following for their numerous reviews and comments to
this document:
o Dr. Stephen Kent
o Dr. Carsten Bormann
o Mr. Lars-Erik Jonnson
o Mr. Pasi Eronen
o Dr. Joseph Touch
7. References
7.1. Normative References
[IPSEC] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[ROHC] Bormann, C., Burmeister, C., Degermark, M., Fukushima, H.,
Hannu, H., Jonsson, L., Hakenberg, R., Koren, T., Le, K.,
Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K.,
Wiebke, T., Yoshimura, T., and H. Zheng, "RObust Header
Compression (ROHC): Framework and four profiles: RTP, UDP,
ESP, and uncompressed", RFC 3095, July 2001.
[IPCOMP] Shacham, A., Monsour, R., Pereira, and Thomas, "IP Payload
Compression Protocol (IPComp)", RFC 3173, September 2001.
[ROHCPPP] Bormann, C., "Robust Header Compression (ROHC) over PPP",
RFC 3241, April 2002.
[IKEV2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[IKEV2EXT]
Pezeshki, J., Ertekin, E., and C. Christou, "Extensions to
IKEv2 to Support Robust Header Compression over IPsec
(RoHCoIPsec)", work in progress , August 2008.
[AH] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[ESP] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
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7.2. Informative References
[ROHCOIPSEC]
Ertekin, E. and C. Christou, "Integration of Header
Compression over IPsec Security Associations", work in
progress , August 2008.
[ROHCPROF]
"RObust Header Compression (ROHC) Profile Identifiers",
www.iana.org/assignments/rohc-pro-ids , October 2005.
[PROTOCOL]
IANA, ""Assigned Internet Protocol Numbers", IANA registry
at: http://www.iana.org/assignments/protocol-numbers".
Authors' Addresses
Emre Ertekin
Booz Allen Hamilton
13200 Woodland Park Dr.
Herndon, VA 20171
US
Email: ertekin_emre@bah.com
Jonah Pezeshki
Booz Allen Hamilton
13200 Woodland Park Dr.
Herndon, VA 20171
US
Email: pezeshki_jonah@bah.com
Michele Casey
Booz Allen Hamilton
13200 Woodland Park Dr.
Herndon, VA 20171
US
Email: casey_michele@bah.com
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Chris Christou
Booz Allen Hamilton
13200 Woodland Park Dr.
Herndon, VA 20171
US
Email: christou_chris@bah.com
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28334
Germany
Email: cabo@tzi.org
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