Internet Engineering Task Force (IETF) R. Gagliano
Request for Comments: 6495 Cisco Systems
Updates: 3971 S. Krishnan
Category: Standards Track Ericsson
ISSN: 2070-1721 A. Kukec
February 2012 Subject Key Identifier (SKI) SEcure Neighbor Discovery (SEND)
Name Type Fields
SEcure Neighbor Discovery (SEND) defines the Name Type field in the
ICMPv6 Trust Anchor option. This document specifies new Name Type
fields based on certificate Subject Key Identifiers (SKIs).
Status of This Memo
This is an Internet Standards Track document.
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received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 22. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 23. Name Type Fields in the ICMPv6 TA Option Defined in This
Document . . . . . . . . . . . . . . . . . . . . . . . . . . . 34. Processing Rules for Routers . . . . . . . . . . . . . . . . . 45. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 46. Security Considerations . . . . . . . . . . . . . . . . . . . . 57. Normative References . . . . . . . . . . . . . . . . . . . . . 51. Introduction
SEcure Neighbor Discovery (SEND) [RFC3971] utilizes X.509v3
certificates that include the [RFC3779] extension for IPv6 addresses
to certify a router's authority over an IPv6 prefix for the NDP
(Neighbor Discovery Protocol). The Trust Anchor (TA) option in
Section 6.4.3 of [RFC3971] allows the identification of the Trust
Anchor selected by the host. In that same section, two name types
were defined: the DER Encoded X.501 Name and a Fully Qualified Domain
In any Public Key Infrastructure, the subject name of a certificate
is only unique within each Certification Authority (CA).
Consequently, a new option to identify TAs across CAs is needed.
In [RFC6494], the certificate profile described in [RFC6487] is
adopted for SEND. In these documents, the Subject field in the
certificates is declared to be meaningless and the subjectAltName
field is not allowed. On the other hand, the Subject Key Identifier
(SKI) extension for the X.509 certificates is defined as mandatory
This document specifies new Name Type fields in the SEND TA option
that allows the use of the SKI X.509 extension to identify TA X.509
certificates. This document also defines experimental and reserved
Name Types values.
Finally, this document updates [RFC3971] by changing the "Trust
Anchor option (Type 15) Name Type field" registration procedures from
Standards Action to Standards Action or IESG Approval [RFC5226].
2. Requirements Notation
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].
3. Name Type Fields in the ICMPv6 TA Option Defined in This Document
The following Name Type fields in the ICMPv6 TA option are defined:
Name Type Description
3 SHA-1 Subject Key Identifier (SKI)
4 SHA-224 Subject Key Identifier (SKI)
5 SHA-256 Subject Key Identifier (SKI)
6 SHA-384 Subject Key Identifier (SKI)
7 SHA-512 Subject Key Identifier (SKI)
Name Type field values 0 and 255 are marked as reserved. This means
that they are not available for allocation.
When the Name Type field is set to 3, the Name Type field contains a
160-bit SHA-1 hash of the value of the DER-encoded ASN.1 bit string
of the subject public key, as described in Section 4.8.2 of
[RFC6487]. Implementations MAY support SHA-1 SKI name type.
When the Name Type field is set to 4, 5, 6, or 7, the hash function
will respectively be: SHA-224, SHA-256, SHA-384, or SHA-512.
Implementations MAY support SHA-224, SHA-256, SHA-384, and SHA-512
SKI name types.
Name Type fields 253 and 254 are marked as experimental, per guidance
4. Processing Rules for Routers
As specified in [RFC3971], a TA is identified by the SEND TA option.
If the TA option is represented as a SKI, then the SKI MUST be equal
to the X.509 SKI extension in the trust anchor's certificate. The
router SHOULD include the TA option(s) in the advertisement for which
the certification path was found. Also, following the specification
defined in [RFC3971], if the router is unable to find a path to the
requested anchor, it SHOULD send an advertisement without any
certificate. In this case, the router SHOULD include the TA options
that were solicited.
5. IANA Considerations
IANA has updated the "Trust Anchor option (Type 15) Name Type field"
registry to include the following values:
| Value | Description |
| 0 | Reserved (Section 3) |
| 3 | SHA-1 Subject Key Identifier (SKI) (Section 3) |
| 4 | SHA-224 Subject Key Identifier (SKI) (Section 3) |
| 5 | SHA-256 Subject Key Identifier (SKI) (Section 3) |
| 6 | SHA-384 Subject Key Identifier (SKI) (Section 3) |
| 7 | SHA-512 Subject Key Identifier (SKI) (Section 3) |
| 253-254 | Experimental Use (Section 3) |
| 255 | Reserved (Section 3) |
Table 1: New Name Type Field Values in the ICMPv6 TA Option
IANA has also modified the registration procedures for the "Trust
Anchor option (Type 15) Name Type field" registry to Standards Action
or IESG Approval [RFC5226].
6. Security Considerations
The hash functions referenced in this document to calculate the SKI
have reasonable random properties in order to provide reasonably
unique identifiers. Two identical identifiers in the same validation
path will cause the router to stop fetching certificates once the
first certificate has been fetched. In the case that the upward
certificate was configured as a TA by a host, the router will send to
this host an incomplete list of certificates, causing the SEND
validation to fail.
For experimental values of the Name Type field, the guidance given in
[RFC3692] about the use of experimental values needs to be followed.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779, June 2004.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
[RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for
X.509 PKIX Resource Certificates", RFC 6487,
[RFC6494] Gagliano, R., Krishnan, S., and A. Kukec, "Certificate
Profile and Certificate Management for SEcure Neighbor
Discovery (SEND)", RFC 6494, February 2012.
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