Host Identity Protocol Heer
Internet-Draft Distributed Systems Group, RWTH
Intended status: Informational Aachen University
Expires: August 21, 2008 Varjonen
Helsinki Institute for Information
Technology
February 18, 2008
HIP Certificates
draft-varjonen-hip-cert-00
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This document specifies a certificate parameter called CERT for the
Host Identity Protocol (HIP). The CERT parameter is a container for
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Simple Public Key Infrastructure (SPKI) and X.509 certificates. It
is used for carrying these certificates in HIP control messages.
Additionally, this document specifies the representations of Host
Identity Tags in SPKI certificates.
Requirements Language
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].
1. Introduction
Digital certificates bind a piece of information to a public key by
means of a digital signature, and thus, enable the holder of a
private key to generate cryptographically verifiable statements. The
Host Identity Protocol (HIP)[I-D.ietf-hip-base] defines a new
cryptographic namespace based on asymmetric cryptography. Each
host's identity is derived from a public key, allowing hosts to
digitally sign data with their private key. This document specifies
the CERT parameter that is used to transmit digital signatures in
HIP. It corresponds to the placeholder specified in
[I-D.ietf-hip-base].
2. CERT Parameter
The CERT parameter is a container for a certain types of digital
certificates. It may either carry SPKI certificates or X.509.v3
certificates. It does not specify any certificate semantics.
However, it defines organizational parameters that help HIP hosts to
transmit semantically grouped parameters.
The CERT parameter may be covered by the HIP SIGNATURE field and is a
non-critical parameter.
Each HIP packet may contain multiple CERT parameters. If these
parameters are related in a way that requires several parameters to
be handled in sequence, the Cert group and the Cert count field must
be set. Ungrouped certificates exhibit a unique Cert group field and
set the Cert count to 1. CERT parameters with the same Cert group
number in the group field indicate a logical grouping. The Cert
count field indicates the number of grouped CERT parameters.
CERT parameters that belong to the same CERT group may be contained
in multiple sequential packets. This is indicated by a higher Cert
count than the amount of CERT parameters with matching Cert group
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fields in a packet. Within a HIP packet, CERT parameters must be
placed in ascending order of their Cert group field. Cert groups may
only span multiple packets if the cert group does not fit the packet.
Only one Cert group may span two subsequent packets.
The Cert ID acts as a sequence number to identify the certificates in
a Cert group. The numbers in the Cert ID field must start from 1 up
to Cert count.
The CERT parameter can be used in I1, R1, I2, R2, and UPDATE
messages.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cert group | Cert count | Cert ID | Cert type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Certificate /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 768
Length Length in octets, excluding Type, Length, and Padding
Cert group Group ID grouping multiple related CERT parameters
Cert count Total count of certificates that are sent, possibly
in several consecutive HIP control packets.
Cert ID The sequence number for this certificate
Cert Type Describes the type of the certificate
Padding Any Padding, if necessary, to make the TLV a multiple
of 8 bytes.
The following certificate types are defined:
+-------------+-------------+
| Cert format | Type number |
+-------------+-------------+
| SPKI | 1 |
| X.509.v3 | 2 |
+-------------+-------------+
All implementations MUST support SPKI. The next section outlines the
use of HITs in SPKI. The wire formats for SPKI are defined in
[SEXP].The encoding format for X.509.v3 certificate is defined
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elsewhere [RFC3280].
3. SPKI cert object and Host Identities
When using SPKI certificates to transmit information relating to HIP
hosts, HITs need to be enclosed within the certificates. In the
following we define the representation of those identifiers for SPKI
given as S-expressions. Note that S-expressions are only the human-
readable representation of SPKI certificates.
The Host Identity Tag of a host is expressed as follows:
Format: (hash hit hit-of-host)
Example: (hash hit 2001:13:724d:f3c0:6ff0:33c2:15d8:5f50)
Below is a simple example of SPKI cert object with HIP content.
(cert
(issuer (hash hit 2001:14:fd64:ca3b:9ef2:8374:ec80:4f20))
(subject (hash hit 2001:13:724d:f3c0:6ff0:33c2:15d8:5f50))
(tag <capability-name_1> (arg <arg_1>)
...
(tag <capability-name_n> (arg <arg_n>)
(propagate)
(online crl http://www.issuersdomain.net/crl)
(not before 1/1/2008)
(not after 12/31/2008)
)
The certificate object has HITs encoded into issuer and subject
fields. Otherwise it is as defined in [SPKI.structure] and [RFC2693]
4. IANA Considerations
This document defines the CERT parameter for the Host Identity
Protocol [I-D.ietf-hip-base]. This parameter is defined in Section 2
with type 768. The parameter type number is also defined in
[I-D.ietf-hip-base]. The Cert Group and Cert ID namespaces are
managed locally by each peer that sends CERT parameters in HIP
packets.
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5. Security Considerations
Certificate grouping allows the certificates to be sent in multiple
consecutive packets. This might allow similar attacks that
fragmentation allows, i.e. sending of fragments in wrong order and
skipping some fragments in order to leave the recipient waiting
something that never comes. This problem can be alleviated by rate
limiting HIP control packets
Using CERT parameter in I1 is not recommended, because it may lead to
workload on the responder. This workload may lead to a denial-of-
service attack.
6. Acknowledgements
The authors would like to thank M. Komu and T. Henderson of fruitful
conversations on the subject.
7. 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.
[RFC2693] Ellison, C., Frantz, B., Lampson, B., Rivest, R., Thomas,
B., and T. Ylonen, "SPKI Certificate Theory", RFC 2693,
September 1999.
[RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[SEXP] Rivest, R., "Code and description of S-expressions",
<http://theory.lcs.mit.edu/~rivest/sexp.html>.
[SPKI.structure]
Ellison, C., "Simple Public Key Certificate",
<draft-ietf-spki-cert-structure-06.txt>.
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Authors' Addresses
Tobias Heer
Distributed Systems Group, RWTH Aachen University
Ahornstrasse 55
Aachen
Germany
Phone: +49 241 80 214 36
Email: heer@cs.rwth-aachem.de
URI: http://ds.cs.rwth-aachen.de/members/heer
Samu Varjonen
Helsinki Institute for Information Technology
Metsnneidonkuja 4
Helsinki
Finland
Fax: +35896949768
Email: samu.varjonen@hiit.fi
URI: http://www.hiit.fi
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