Internet DRAFT - draft-dawkins-hip-checksum-coverage
draft-dawkins-hip-checksum-coverage
Network Working Group X. Jiang
Internet-Draft Huawei
Intended status: Informational P. Matthews
Expires: May 13, 2008 Avaya
S. Dawkins, Ed.
Huawei (USA)
November 10, 2007
Proposed Host Identity Protocol (HIP) Checksum Coverage
draft-dawkins-hip-checksum-coverage-00
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Copyright (C) The IETF Trust (2007).
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Abstract
This specification suggests two changes to the Host Identity Protocol
(HIP) checksum calculation. Specifically, only the HIP header and
payload fields would be included in the checksum calculation, and the
CRC32c algorithm would be used to compute the checksum. The HIP
version number would be incremented if these suggestions are
accepted, to reflect a different checksum algorithm.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology used in this document . . . . . . . . . . . . . . 4
3. Background for this Proposal . . . . . . . . . . . . . . . . . 5
4. Changes to Checksum Coverage . . . . . . . . . . . . . . . . . 7
5. Proposed HIP Checksum Coverage . . . . . . . . . . . . . . . . 8
6. Proposed HIP Version Change . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Introduction
This specification suggests two changes to the Host Identity Protocol
(HIP) checksum calculation. Each of these changes should be
considered separately:
1. A change to the checksum coverage in HIP, and
2. Replacing the 16-bit checksum with a CRC32c checksum.
The HIP version number would be incremented if these suggestions are
accepted, to reflect a different checksum algorithm.
The checksum calculation described in this specification is used only
when HIP is carried directly over IP. Considerations for checksum
calculations when an intervening transport protocol is used are left
to [I-D.ietf-hip-nat-traversal].
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2. Terminology 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].
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3. Background for this Proposal
In section 5.1.1, the HIP base protocol draft [I-D.ietf-hip-base] now
specifies the following:
Since the checksum covers the source and destination addresses in
the IP header, it must be recomputed on HIP-aware NAT devices.
If IPv6 is used to carry the HIP packet, the pseudo-header
[RFC2460] contains the source and destination IPv6 addresses, HIP
packet length in the pseudo-header length field, a zero field, and
the HIP protocol number (see Section 4) in the Next Header field.
The length field is in bytes and can be calculated from the HIP
header length field: (HIP Header Length + 1) * 8.
In case of using IPv4, the IPv4 UDP pseudo header format [RFC0768]
is used. In the pseudo header, the source and destination
addresses are those used in the IP header, the zero field is
obviously zero, the protocol is the HIP protocol number (see
Section 4), and the length is calculated as in the IPv6 case.
Although the use of pseudo-headers in transport checksums has been
universal practice for decades, this design choice is proving
problematic for several applications that perform HIP-level packet
relays. For example:
o There are two active proposals in the HIP working group itself
that require forwarding of HIP packets, "Host Identity Protocol
(HIP) Rendezvous Extension" ([I-D.ietf-hip-rvs]) and "HIP
Extensions for the Traversal of Network Address Translators"
([I-D.ietf-hip-nat-traversal]).
o Other HIP applications would also benefit. For example, the HIP-
HOP proposal in the P2PSIP working group
([I-D.matthews-p2psip-hip-hop])includes a mechanism that allows
intermediate peers to route HIP packets between peers that does
not have an active direct connection (for various reasons,
including but not limited to NAT traversal issues).
Although a HIP-level relay is attractive for these mechanisms, the
HIP packet checksum is recomputed at each relay, because the source
and destination IP addresses are currently included in the pseudo-
header covered by the HIP checksum.
In addition to the checksum calculation overhead at each relay,
intermediate recalculation means that checksum protection only covers
the part of the path to the next HIP-aware device that recalculates
the checksum.
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We also note that excluding the source and destination IP addresses
from the HIP checksum calculation would improve the ability of HIP
connections to survive interface selection changes, would better
accommodate multihoming, and would better detect checksum failures in
scenarios where intermediate nodes forward at the HIP layer. For
example, in [I-D.ietf-hip-nat-traversal], checksums are recalculated
when packets traverse HIP-aware NATs (so checksums do not protect the
packets over an entire end-to-end path) and checksums are set to 0
when packets traverse HIP-unaware NATs (so that checksums are
disabled completely).
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4. Changes to Checksum Coverage
This specification recommends removing pseudo-header fields from the
checksum calculation, so that the checksum does not need to be
recalculated when pseudo-header field values change. Most important
(and probably most controversial) is the removal of source and
destination IP addresses from the checksum calculation.
The only bytes included in the checksum calculation are the HIP
header and HIP payload bytes.
The resulting checksum does protect the HIP header and HIP payload,
but does not protect the pseudo-header fields associated with the HIP
header and HIP payload. The resulting checksum is "end-to-end" - it
protects the HIP header and HIP payload for packets that traverse HIP
relays, where the current checksum calculation does not - it is
recalculated at each HIP relay, so errors at intermediate HIP relays
may not be caught if the checksum was recalculated after the error
was introduced at the HIP relay.
We believe that removal of the source and destination IP addresses
from the transport checksum calculation is a reasonable change to the
HIP protocol. If these fields are exluded from the transport
checksum calculation, we see no reason to include other IP-level
fields as part of a transport pseudo-header in the checksum
calculation.
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5. Proposed HIP Checksum Coverage
This proposal uses the same checksum algorithm that is used in SCTP,
except that no pseudo-header fields are prepended to the HIP header
and payload before the checksum is calculated.
Note that the current HIP base specification uses a 16-bit checksum
field. This checksum field must be expanded to 32 bits, in order to
accommodate the crc32c checksum (also used by SCTP). Also note that
a reserved field is also added to preserve 8-byte alignment, as
required in [RFC2460] to ensure alignment of subsequent IPv6
extension headers.
The resulting modified header format is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Header Length |0| Packet Type | VER. | RES.|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Controls | (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver's Host Identity Tag (HIT) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ HIP Parameters /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following text is taken from [RFC4960], with modifications
(reflecting its use for HIP):
When sending a HIP packet, the endpoint MUST strengthen the data
integrity of the transmission by including the crc32c checksum value
calculated on the packet, as described below.
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After the packet is constructed, the transmitter shall:
1. Initialize the checksum field to 0's.
2. Calculate the crc32c checksum of the HIP header and HIP payload.
Refer to appendix B of [RFC4960] for details of the crc32c
algorithm. And,
3. Put the resultant value into the checksum field, and leave the
rest of the bits unchanged.
When a HIP packet is received, the receiver MUST first check the
crc32c checksum:
1. Store the received crc32c checksum value aside,
2. Replace the 32 bits of the checksum field in the received HIP
packet with all '0's and calculate an crc32c checksum value of
the HIP header and payload. And,
3. Verify that the calculated crc32c checksum is the same as the
received crc32c checksum. If not, the receiver MUST treat the
packet as an invalid HIP packet.
The default procedure for handling invalid HIP packets is to silently
discard them.
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6. Proposed HIP Version Change
Because this change is not backward-compatible with current HIP
specifications ([I-D.ietf-hip-base]) or with conformant
implementations to this specification, we recommend changing the HIP
version number from 1 to 2 for packets processed using this
specification.
Although it is certainly possible to make this change backward-
compatible by adding a version negotiation mechanism and continuing
to use HIP Version 1 with hosts that do not respond to the
negotiation mechanism, we believe that making this change to HIP at
this time, without providing such a negotiation mechanism, is
appropriate because
1. The base HIP protocol specification is still an Internet Draft,
as of this writing,
2. The base HIP protocol specification is currently targeted at the
Experimental track, so that the usual RFC 2026 considerations
about incompatible changes to Standards-track protocols should
not apply, and
3. The change is small and localized to setting/verifying the HIP
version number itself, plus computing and verifying the HIP
checksum.
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7. Security Considerations
The following security considerations are in addition to the security
considerations identified in the base HIP protocol specification
([I-D.ietf-hip-base]).
This change to the HIP checksum coverage does make source and
destination IP addresses less "visible" to a receiving host, but this
is judged to be an acceptable risk, for these reasons:
1. Off-path attackers must provide two 128-bit numbers (the source
and destination HITs) that the host under attack will recognize
as legitimate HITs. If the attacker sends packets with HITs that
the host under attack does not recognize, these packets are
simply dropped as invalid packets - a MUST in
[I-D.ietf-hip-base]. Given that each of the two numbers is self-
cerifying because it is the hash of a public key, this attack is
seen as computationally hard.
2. On-path attackers who are able to learn valid source and
destination HITs, in order to forge packets that might be used
for denial of service attacks, etc. can already do much worse
than forge packets - they can simply drop packets, or execute
denial of service attacks on intermediate devices that would
forward legitimate packets in normal operation.
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8. IANA Considerations
The current HIP base protocol specification ([I-D.ietf-hip-base])
includes as part of its IANA considerations a request that IANA
create a new namespace for HIP Version Numbers, and add an entry for
HIP Version 1. This specification defines HIP Version 2, so we also
request an entry in this namespace for HIP Version 2, as described in
this specification.
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9. References
9.1. Normative References
[I-D.ietf-hip-base]
Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
"Host Identity Protocol", draft-ietf-hip-base-10 (work in
progress), October 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 2007.
9.2. Informative References
[I-D.ietf-hip-nat-traversal]
Schmitt, V., "HIP Extensions for the Traversal of Network
Address Translators", draft-ietf-hip-nat-traversal-02
(work in progress), July 2007.
[I-D.ietf-hip-rvs]
Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
Rendezvous Extension", draft-ietf-hip-rvs-05 (work in
progress), June 2006.
[I-D.matthews-p2psip-hip-hop]
Cooper, E., "A Distributed Transport Function in P2PSIP
using HIP for Multi-Hop Overlay Routing",
draft-matthews-p2psip-hip-hop-00 (work in progress),
June 2007.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
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Authors' Addresses
XingFeng Jiang
Huawei Technologies
Huihong Mansion,No.91 Baixia Rd
Nanjing, Jiangsu 210001
P. R. China
Phone: +86(25)84565462
Email: jiang.x.f@huawei.com
Philip Matthews
Avaya
100 Innovation Drive
Ottawa, Ontario K2K 3G7
Canada
Phone: +1 613 592 4343 x224
Email: philip_matthews@magma.ca
Spencer Dawkins (editor)
Huawei Technologies (USA)
1547 Rivercrest Blvd.
Allen, TX 75002
USA
Phone: +1 214 755 3870
Email: spencer@mcsr-labs.org
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