Network Working Group E. Ertekin
Internet-Draft C. Christou
Expires: August 6, 2009 Booz Allen Hamilton
C. Bormann
Universitaet Bremen TZI
February 2, 2009
IPsec Extensions to Support Robust Header Compression over IPsec
(ROHCoIPsec)
draft-ietf-rohc-ipsec-extensions-hcoipsec-04
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Abstract
Integrating ROHC with IPsec (ROHCoIPsec) offers the combined benefits
of IP security services and efficient bandwidth utilization.
However, in order to integrate ROHC with IPsec, extensions to the SPD
and SAD are required. This document describes the IPsec extensions
required to support ROHCoIPsec.
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 . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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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). For ROHCoIPsec, 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 to ensure the integrity of the decompressed
packet is needed. 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 security and header compression services
that are provided to packets.
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 following ROHC channel parameters must be included if the
processing info field in the SPD is set to PROTECT (suggested values
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for these parameters are consistent with [ROHCPPP]):
MAX_CID: The field indicates the highest context ID that will be
decompressed by the local decompressor. 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 field is a list of ROHC profiles supported by the
local decompressor. Possible values for this list are contained
in the [ROHCPROF] registry.
In addition to these ROHC channel parameters, a field within the SPD
is required to store a list of integrity algorithms supported by the
ROHCoIPsec instance:
INTEGRITY ALGORITHM: This field is a list of integrity algorithms
supported by the ROHCoIPsec instance. This will be used by the
ROHC process to ensure that packet headers are properly
decompressed (see Section 3.2).
Several other ROHC channel parameters are omitted from the SPD,
because they are set implicitly. The omitted channel parameters are
LARGE_CIDS, MRRU, and FEEDBACK_FOR. The LARGE_CIDS channel parameter
is set implicitly, based on the value of MAX_CID (e.g. if MAX_CID is
<= 15, LARGE_CIDS is assumed to be 0). Furthermore, since in-order
delivery of ROHC packets cannot be guaranteed, the MRRU parameter
must be set to 0 (as stated in Section 5.2.5.1 of [ROHC] and Section
6.1 of [ROHCV2]). Finally, the ROHC FEEDBACK_FOR channel parameter
is set implicitly to the ROHC channel associated with the SA in the
reverse direction. If an SA in the reverse direction does not exist,
the FEEDBACK_FOR channel parameter is not set, and ROHC must not
operate in bidirectional Mode.
2.2. Security Association Database (SAD)
Each entry within the SAD defines the parameters associated with each
established SA. Unless 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.
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" that contains the parameters
used by ROHC instance. The ROHC Data Item exists for both inbound
and outbound SAs.
The ROHC Data Item includes the ROHC channel parameters for the SA.
These channel parameters (i.e., MAX_CID, PROFILES) are enumerated
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above in Section 2.1. For inbound SAs, the ROHC Data Item includes
ROHC channel parameters that are used by the local decompressor
instance; conversely, for outbound SAs, the ROHC Data Item includes
ROHC channel parameters that are used by local compressor instance.
In addition to these ROHC channel parameters, the ROHC Data Item for
both inbound and outbound SAs includes two additional parameters.
Specifically, these parameters store the integrity algorithm and
respective key used by ROHC (see Section 3.2). The integrity
algorithm and its associated key are used to calculate a ROHC ICV;
this ICV is used to verify the packet headers post-decompression.
Finally, for inbound SAs, the ROHC Data Item includes a FEEDBACK_FOR
parameter. The parameter is a reference to a ROHC channel in the
opposite direction (i.e., the outbound SA) between the same
compression endpoints. A ROHC channel associated with an inbound SA
and a ROHC channel associated with an outbound SA may be coupled to
form a Bi-directional ROHC channel as defined in Section 6.1 and
Section 6.2 in [ROHC-TERM].
"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 signaling 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 identifier.
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, in order to determine if it
requires ROHC decompression.
3.2. Verifying the Integrity of Decompressed Packet Headers
Since ROHC is inherently a lossy compression algorithm, ROHCoIPsec
may use an additional Integrity Algorithm (and respective key) to
compute a second Integrity Check Value (ICV) for the uncompressed
packet. This ICV is computed over the uncompressed IP header, as
well at the higher-layer headers and the packet payload, and is
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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
appended 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
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 must not 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 header(s) is(are) 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
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o Packet header(s) is(are) decompressed by the ROHC process
o The decompressed packet is used with the integrity algorithm (and
its respective key) to compute a ROHC ICV that is compared to the
appended 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 following steps must be followed
for outbound and inbound packets.
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.
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. This technique, however, reduces the overall efficiency
benefit offered by header compression.
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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
document.
The authors would also like to thank Mr. Yoav Nir, and Mr. Robert A
Stangarone Jr.: both served as committed document reviewers for this
specification.
Finally, the authors would like to thank the following for their
numerous reviews and comments to this document:
o Dr. Stephen Kent
o Mr. Lars-Erik Jonsson
o Mr. Carl Knutsson
o Mr. Pasi Eronen
o Dr. Jonah Pezeshki
o Mr. Tero Kivinen
o Dr. Joseph Touch
o Mr. Rohan Jasani
7. References
7.1. Normative References
[IPSEC] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[ROHC] Jonsson, L-E., Pelletier, G., and K. Sandlund, "The RObust
Header Compression (ROHC) Framework", RFC 4995, July 2007.
[ROHCV2] Pelletier, G. and K. Sandlund, "RObust Header Compression
Version 2 (ROHCv2): Profiles for RTP, UDP, IP, ESP and
UDP-Lite", RFC 5225.
[IPCOMP] Shacham, A., Monsour, R., Pereira, and Thomas, "IP Payload
Compression Protocol (IPComp)", RFC 3173, September 2001.
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[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]
Ertekin, et al., "Extensions to IKEv2 to Support Robust
Header Compression over IPsec (ROHCoIPsec)", work in
progress , February 2009.
[AH] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[ESP] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
7.2. Informative References
[ROHCOIPSEC]
Ertekin, E., Jasani, R., Christou, C., and C. Bormann,
"Integration of Header Compression over IPsec Security
Associations", work in progress , February 2009.
[ROHCPROF]
"RObust Header Compression (ROHC) Profile Identifiers",
www.iana.org/assignments/rohc-pro-ids , October 2005.
[ROHC-TERM]
Jonsson, L-E., "Robust Header Compression (ROHC):
Terminology and Channel Mapping Examples", RFC 3759,
April 2004.
[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
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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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