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<pre>Network Working Group P. Nikander
Request for Comments: 5205 Ericsson Research NomadicLab
Category: Experimental J. Laganier
DoCoMo Euro-Labs
April 2008
<span class="h1">Host Identity Protocol (HIP) Domain Name System (DNS) Extension</span>
Status of This Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Abstract
This document specifies a new resource record (RR) for the Domain
Name System (DNS), and how to use it with the Host Identity Protocol
(HIP). This RR allows a HIP node to store in the DNS its Host
Identity (HI, the public component of the node public-private key
pair), Host Identity Tag (HIT, a truncated hash of its public key),
and the Domain Names of its rendezvous servers (RVSs).
<span class="grey">Nikander & Laganier Experimental [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
Table of Contents
<a href="#section-1">1</a>. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-2">2</a>. Conventions Used in This Document . . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-3">3</a>. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-3.1">3.1</a>. Simple Static Singly Homed End-Host . . . . . . . . . . . <a href="#page-5">5</a>
<a href="#section-3.2">3.2</a>. Mobile end-host . . . . . . . . . . . . . . . . . . . . . <a href="#page-6">6</a>
<a href="#section-4">4</a>. Overview of Using the DNS with HIP . . . . . . . . . . . . . . <a href="#page-8">8</a>
<a href="#section-4.1">4.1</a>. Storing HI, HIT, and RVS in the DNS . . . . . . . . . . . <a href="#page-8">8</a>
<a href="#section-4.2">4.2</a>. Initiating Connections Based on DNS Names . . . . . . . . <a href="#page-8">8</a>
<a href="#section-5">5</a>. HIP RR Storage Format . . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-5.1">5.1</a>. HIT Length Format . . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-5.2">5.2</a>. PK Algorithm Format . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-5.3">5.3</a>. PK Length Format . . . . . . . . . . . . . . . . . . . . . <a href="#page-10">10</a>
<a href="#section-5.4">5.4</a>. HIT Format . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-10">10</a>
<a href="#section-5.5">5.5</a>. Public Key Format . . . . . . . . . . . . . . . . . . . . <a href="#page-10">10</a>
<a href="#section-5.6">5.6</a>. Rendezvous Servers Format . . . . . . . . . . . . . . . . <a href="#page-10">10</a>
<a href="#section-6">6</a>. HIP RR Presentation Format . . . . . . . . . . . . . . . . . . <a href="#page-10">10</a>
<a href="#section-7">7</a>. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-11">11</a>
<a href="#section-8">8</a>. Security Considerations . . . . . . . . . . . . . . . . . . . <a href="#page-12">12</a>
<a href="#section-8.1">8.1</a>. Attacker Tampering with an Insecure HIP RR . . . . . . . . <a href="#page-12">12</a>
<a href="#section-8.2">8.2</a>. Hash and HITs Collisions . . . . . . . . . . . . . . . . . <a href="#page-13">13</a>
<a href="#section-8.3">8.3</a>. DNSSEC . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-13">13</a>
<a href="#section-9">9</a>. IANA Considerations . . . . . . . . . . . . . . . . . . . . . <a href="#page-13">13</a>
<a href="#section-10">10</a>. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-14">14</a>
<a href="#section-11">11</a>. References . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-14">14</a>
<a href="#section-11.1">11.1</a>. Normative references . . . . . . . . . . . . . . . . . . . <a href="#page-14">14</a>
<a href="#section-11.2">11.2</a>. Informative references . . . . . . . . . . . . . . . . . . <a href="#page-15">15</a>
<span class="grey">Nikander & Laganier Experimental [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
This document specifies a new resource record (RR) for the Domain
Name System (DNS) [<a href="./rfc1034" title=""Domain names - concepts and facilities"">RFC1034</a>], and how to use it with the Host Identity
Protocol (HIP) [<a href="./rfc5201" title=""Host Identity Protocol"">RFC5201</a>]. This RR allows a HIP node to store in the
DNS its Host Identity (HI, the public component of the node public-
private key pair), Host Identity Tag (HIT, a truncated hash of its
HI), and the Domain Names of its rendezvous servers (RVSs) [<a href="./rfc5204" title=""Host Identity Protocol (HIP) Rendezvous Extension"">RFC5204</a>].
Currently, most of the Internet applications that need to communicate
with a remote host first translate a domain name (often obtained via
user input) into one or more IP address(es). This step occurs prior
to communication with the remote host, and relies on a DNS lookup.
With HIP, IP addresses are intended to be used mostly for on-the-wire
communication between end hosts, while most Upper Layer Protocols
(ULP) and applications use HIs or HITs instead (ICMP might be an
example of an ULP not using them). Consequently, we need a means to
translate a domain name into an HI. Using the DNS for this
translation is pretty straightforward: We define a new HIP resource
record. Upon query by an application or ULP for a name to IP address
lookup, the resolver would then additionally perform a name to HI
lookup, and use it to construct the resulting HI to IP address
mapping (which is internal to the HIP layer). The HIP layer uses the
HI to IP address mapping to translate HIs and HITs into IP addresses
and vice versa.
The HIP Rendezvous Extension [<a href="./rfc5204" title=""Host Identity Protocol (HIP) Rendezvous Extension"">RFC5204</a>] allows a HIP node to be
reached via the IP address(es) of a third party, the node's
rendezvous server (RVS). An Initiator willing to establish a HIP
association with a Responder served by an RVS would typically
initiate a HIP exchange by sending an I1 towards the RVS IP address
rather than towards the Responder IP address. Consequently, we need
a means to find the name of a rendezvous server for a given host
name.
This document introduces the new HIP DNS resource record to store the
Rendezvous Server (RVS), Host Identity (HI), and Host Identity Tag
(HIT) information.
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Conventions Used in This Document</span>
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 <a href="./rfc2119">RFC 2119</a> [<a href="./rfc2119" title=""Key words for use in RFCs to Indicate Requirement Levels"">RFC2119</a>].
<span class="grey">Nikander & Laganier Experimental [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. Usage Scenarios</span>
In this section, we briefly introduce a number of usage scenarios
where the DNS is useful with the Host Identity Protocol.
With HIP, most applications and ULPs are unaware of the IP addresses
used to carry packets on the wire. Consequently, a HIP node could
take advantage of having multiple IP addresses for fail-over,
redundancy, mobility, or renumbering, in a manner that is transparent
to most ULPs and applications (because they are bound to HIs; hence,
they are agnostic to these IP address changes).
In these situations, for a node to be reachable by reference to its
Fully Qualified Domain Name (FQDN), the following information should
be stored in the DNS:
o A set of IP address(es) via A [<a href="./rfc1035" title=""Domain names - implementation and specification"">RFC1035</a>] and AAAA [<a href="./rfc3596" title=""DNS Extensions to Support IP Version 6"">RFC3596</a>] RR sets
(RRSets [<a href="./rfc2181" title=""Clarifications to the DNS Specification"">RFC2181</a>]).
o A Host Identity (HI), Host Identity Tag (HIT), and possibly a set
of rendezvous servers (RVS) through HIP RRs.
When a HIP node wants to initiate communication with another HIP
node, it first needs to perform a HIP base exchange to set up a HIP
association towards its peer. Although such an exchange can be
initiated opportunistically, i.e., without prior knowledge of the
Responder's HI, by doing so both nodes knowingly risk man-in-the-
middle attacks on the HIP exchange. To prevent these attacks, it is
recommended that the Initiator first obtain the HI of the Responder,
and then initiate the exchange. This can be done, for example,
through manual configuration or DNS lookups. Hence, a new HIP RR is
introduced.
When a HIP node is frequently changing its IP address(es), the
natural DNS latency for propagating changes may prevent it from
publishing its new IP address(es) in the DNS. For solving this
problem, the HIP Architecture [<a href="./rfc4423" title=""Host Identity Protocol (HIP) Architecture"">RFC4423</a>] introduces rendezvous servers
(RVSs) [<a href="./rfc5204" title=""Host Identity Protocol (HIP) Rendezvous Extension"">RFC5204</a>]. A HIP host uses a rendezvous server as a
rendezvous point to maintain reachability with possible HIP
initiators while moving [<a href="./rfc5206" title=""End-Host Mobility and Multihoming with the Host Identity Protocol"">RFC5206</a>]. Such a HIP node would publish in
the DNS its RVS domain name(s) in a HIP RR, while keeping its RVS up-
to-date with its current set of IP addresses.
When a HIP node wants to initiate a HIP exchange with a Responder, it
will perform a number of DNS lookups. Depending on the type of
implementation, the order in which those lookups will be issued may
vary. For instance, implementations using HIT in APIs may typically
first query for HIP resource records at the Responder FQDN, while
<span class="grey">Nikander & Laganier Experimental [Page 4]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-5" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
those using an IP address in APIs may typically first query for A
and/or AAAA resource records.
In the following, we assume that the Initiator first queries for HIP
resource records at the Responder FQDN.
If the query for the HIP type was responded to with a DNS answer with
RCODE=3 (Name Error), then the Responder's information is not present
in the DNS and further queries for the same owner name SHOULD NOT be
made.
In case the query for the HIP records returned a DNS answer with
RCODE=0 (No Error) and an empty answer section, it means that no HIP
information is available at the responder name. In such a case, if
the Initiator has been configured with a policy to fallback to
opportunistic HIP (initiating without knowing the Responder's HI) or
plain IP, it would send out more queries for A and AAAA types at the
Responder's FQDN.
Depending on the combinations of answers, the situations described in
<a href="#section-3.1">Section 3.1</a> and <a href="#section-3.2">Section 3.2</a> can occur.
Note that storing HIP RR information in the DNS at an FQDN that is
assigned to a non-HIP node might have ill effects on its reachability
by HIP nodes.
<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>. Simple Static Singly Homed End-Host</span>
A HIP node (R) with a single static network attachment, wishing to be
reachable by reference to its FQDN (www.example.com), would store in
the DNS, in addition to its IP address(es) (IP-R), its Host Identity
(HI-R) and Host Identity Tag (HIT-R) in a HIP resource record.
An Initiator willing to associate with a node would typically issue
the following queries:
o QNAME=www.example.com, QTYPE=HIP
o (QCLASS=IN is assumed and omitted from the examples)
Which returns a DNS packet with RCODE=0 and one or more HIP RRs with
the HIT and HI (e.g., HIT-R and HI-R) of the Responder in the answer
section, but no RVS.
<span class="grey">Nikander & Laganier Experimental [Page 5]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-6" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
o QNAME=www.example.com, QTYPE=A QNAME=www.example.com, QTYPE=AAAA
Which returns DNS packets with RCODE=0 and one or more A or AAAA RRs
containing IP address(es) of the Responder (e.g., IP-R) in the answer
section.
Caption: In the remainder of this document, for the sake of keeping
diagrams simple and concise, several DNS queries and answers
are represented as one single transaction, while in fact
there are several queries and answers flowing back and
forth, as described in the textual examples.
[HIP? A? ]
[www.example.com] +-----+
+-------------------------------->| |
| | DNS |
| +-------------------------------| |
| | [HIP? A? ] +-----+
| | [www.example.com]
| | [HIP HIT-R HI-R ]
| | [A IP-R ]
| v
+-----+ +-----+
| |--------------I1------------->| |
| I |<-------------R1--------------| R |
| |--------------I2------------->| |
| |<-------------R2--------------| |
+-----+ +-----+
Static Singly Homed Host
The Initiator would then send an I1 to the Responder's IP addresses
(IP-R).
<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>. Mobile end-host</span>
A mobile HIP node (R) wishing to be reachable by reference to its
FQDN (www.example.com) would store in the DNS, possibly in addition
to its IP address(es) (IP-R), its HI (HI-R), HIT (HIT-R), and the
domain name(s) of its rendezvous server(s) (e.g., rvs.example.com) in
HIP resource record(s). The mobile HIP node also needs to notify its
rendezvous servers of any change in its set of IP address(es).
An Initiator willing to associate with such a mobile node would
typically issue the following queries:
o QNAME=www.example.com, QTYPE=HIP
<span class="grey">Nikander & Laganier Experimental [Page 6]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-7" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
Which returns a DNS packet with RCODE=0 and one or more HIP RRs with
the HIT, HI, and RVS domain name(s) (e.g., HIT-R, HI-R, and
rvs.example.com) of the Responder in the answer section.
o QNAME=rvs.example.com, QTYPE=A QNAME=www.example.com, QTYPE=AAAA
Which returns DNS packets with RCODE=0 and one or more A or AAAA RRs
containing IP address(es) of the Responder's RVS (e.g., IP-RVS) in
the answer section.
[HIP? ]
[www.example.com]
[A? ]
[rvs.example.com] +-----+
+----------------------------------------->| |
| | DNS |
| +----------------------------------------| |
| | [HIP? ] +-----+
| | [www.example.com ]
| | [HIP HIT-R HI-R rvs.example.com]
| |
| | [A? ]
| | [rvs.example.com]
| | [A IP-RVS ]
| |
| | +-----+
| | +------I1----->| RVS |-----I1------+
| | | +-----+ |
| | | |
| | | |
| v | v
+-----+ +-----+
| |<---------------R1------------| |
| I |----------------I2----------->| R |
| |<---------------R2------------| |
+-----+ +-----+
Mobile End-Host
The Initiator would then send an I1 to the RVS IP address (IP-RVS).
Following, the RVS will relay the I1 up to the mobile node's IP
address (IP-R), which will complete the HIP exchange.
<span class="grey">Nikander & Laganier Experimental [Page 7]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-8" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Overview of Using the DNS with HIP</span>
<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>. Storing HI, HIT, and RVS in the DNS</span>
For any HIP node, its Host Identity (HI), the associated Host
Identity Tag (HIT), and the FQDN of its possible RVSs can be stored
in a DNS HIP RR. Any conforming implementation may store a Host
Identity (HI) and its associated Host Identity Tag (HIT) in a DNS HIP
RDATA format. HI and HIT are defined in <a href="#section-3">Section 3</a> of the HIP
specification [<a href="./rfc5201" title=""Host Identity Protocol"">RFC5201</a>].
Upon return of a HIP RR, a host MUST always calculate the HI-
derivative HIT to be used in the HIP exchange, as specified in
<a href="#section-3">Section 3</a> of the HIP specification [<a href="./rfc5201" title=""Host Identity Protocol"">RFC5201</a>], while the HIT possibly
embedded along SHOULD only be used as an optimization (e.g., table
lookup).
The HIP resource record may also contain one or more domain name(s)
of rendezvous server(s) towards which HIP I1 packets might be sent to
trigger the establishment of an association with the entity named by
this resource record [<a href="./rfc5204" title=""Host Identity Protocol (HIP) Rendezvous Extension"">RFC5204</a>].
The rendezvous server field of the HIP resource record stored at a
given owner name MAY include the owner name itself. A semantically
equivalent situation occurs if no rendezvous server is present in the
HIP resource record stored at that owner name. Such situations occur
in two cases:
o The host is mobile, and the A and/or AAAA resource record(s)
stored at its host name contain the IP address(es) of its
rendezvous server rather than its own one.
o The host is stationary, and can be reached directly at the IP
address(es) contained in the A and/or AAAA resource record(s)
stored at its host name. This is a degenerated case of rendezvous
service where the host somewhat acts as a rendezvous server for
itself.
An RVS receiving such an I1 would then relay it to the appropriate
Responder (the owner of the I1 receiver HIT). The Responder will
then complete the exchange with the Initiator, typically without
ongoing help from the RVS.
<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a>. Initiating Connections Based on DNS Names</span>
On a HIP node, a Host Identity Protocol exchange SHOULD be initiated
whenever a ULP attempts to communicate with an entity and the DNS
lookup returns HIP resource records.
<span class="grey">Nikander & Laganier Experimental [Page 8]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-9" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. HIP RR Storage Format</span>
The RDATA for a HIP RR consists of a public key algorithm type, the
HIT length, a HIT, a public key, and optionally one or more
rendezvous server(s).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HIT length | PK algorithm | PK length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ HIT ~
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+ +
| Public Key |
~ ~
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
~ Rendezvous Servers ~
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+
The HIT length, PK algorithm, PK length, HIT, and Public Key fields
are REQUIRED. The Rendezvous Servers field is OPTIONAL.
<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>. HIT Length Format</span>
The HIT length indicates the length in bytes of the HIT field. This
is an 8-bit unsigned integer.
<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>. PK Algorithm Format</span>
The PK algorithm field indicates the public key cryptographic
algorithm and the implied public key field format. This is an 8-bit
unsigned integer. This document reuses the values defined for the
'algorithm type' of the IPSECKEY RR [<a href="./rfc4025" title=""A Method for Storing IPsec Keying Material in DNS"">RFC4025</a>].
Presently defined values are listed in <a href="#section-9">Section 9</a> for reference.
<span class="grey">Nikander & Laganier Experimental [Page 9]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-10" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
<span class="h3"><a class="selflink" id="section-5.3" href="#section-5.3">5.3</a>. PK Length Format</span>
The PK length indicates the length in bytes of the Public key field.
This is a 16-bit unsigned integer in network byte order.
<span class="h3"><a class="selflink" id="section-5.4" href="#section-5.4">5.4</a>. HIT Format</span>
The HIT is stored as a binary value in network byte order.
<span class="h3"><a class="selflink" id="section-5.5" href="#section-5.5">5.5</a>. Public Key Format</span>
Both of the public key types defined in this document (RSA and DSA)
reuse the public key formats defined for the IPSECKEY RR [<a href="./rfc4025" title=""A Method for Storing IPsec Keying Material in DNS"">RFC4025</a>].
The DSA key format is defined in <a href="./rfc2536">RFC 2536</a> [<a href="./rfc2536" title=""DSA KEYs and SIGs in the Domain Name System (DNS)"">RFC2536</a>].
The RSA key format is defined in <a href="./rfc3110">RFC 3110</a> [<a href="./rfc3110" title=""RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS)"">RFC3110</a>] and the RSA key
size limit (4096 bits) is relaxed in the IPSECKEY RR [<a href="./rfc4025" title=""A Method for Storing IPsec Keying Material in DNS"">RFC4025</a>]
specification.
<span class="h3"><a class="selflink" id="section-5.6" href="#section-5.6">5.6</a>. Rendezvous Servers Format</span>
The Rendezvous Servers field indicates one or more variable length
wire-encoded domain names of rendezvous server(s), as described in
<a href="./rfc1035#section-3.3">Section 3.3 of RFC 1035</a> [<a href="./rfc1035" title=""Domain names - implementation and specification"">RFC1035</a>]. The wire-encoded format is self-
describing, so the length is implicit. The domain names MUST NOT be
compressed. The rendezvous server(s) are listed in order of
preference (i.e., first rendezvous server(s) are preferred), defining
an implicit order amongst rendezvous servers of a single RR. When
multiple HIP RRs are present at the same owner name, this implicit
order of rendezvous servers within an RR MUST NOT be used to infer a
preference order between rendezvous servers stored in different RRs.
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. HIP RR Presentation Format</span>
This section specifies the representation of the HIP RR in a zone
master file.
The HIT length field is not represented, as it is implicitly known
thanks to the HIT field representation.
The PK algorithm field is represented as unsigned integers.
The HIT field is represented as the Base16 encoding [<a href="./rfc4648" title=""The Base16, Base32, and Base64 Data Encodings"">RFC4648</a>] (a.k.a.
hex or hexadecimal) of the HIT. The encoding MUST NOT contain
whitespaces to distinguish it from the public key field.
<span class="grey">Nikander & Laganier Experimental [Page 10]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-11" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
The Public Key field is represented as the Base64 encoding [<a href="./rfc4648" title=""The Base16, Base32, and Base64 Data Encodings"">RFC4648</a>]
of the public key. The encoding MUST NOT contain whitespace(s) to
distinguish it from the Rendezvous Servers field.
The PK length field is not represented, as it is implicitly known
thanks to the Public key field representation containing no
whitespaces.
The Rendezvous Servers field is represented by one or more domain
name(s) separated by whitespace(s).
The complete representation of the HPIHI record is:
IN HIP ( pk-algorithm
base16-encoded-hit
base64-encoded-public-key
rendezvous-server[1]
...
rendezvous-server[n] )
When no RVSs are present, the representation of the HPIHI record is:
IN HIP ( pk-algorithm
base16-encoded-hit
base64-encoded-public-key )
<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. Examples</span>
In the examples below, the public key field containing no whitespace
is wrapped since it does not fit in a single line of this document.
Example of a node with HI and HIT but no RVS:
www.example.com. IN HIP ( 2 200100107B1A74DF365639CC39F1D578
AwEAAbdxyhNuSutc5EMzxTs9LBPCIkOFH8cIvM4p
9+LrV4e19WzK00+CI6zBCQTdtWsuxKbWIy87UOoJTwkUs7lBu+Upr1gsNrut79ryra+bSRGQ
b1slImA8YVJyuIDsj7kwzG7jnERNqnWxZ48AWkskmdHaVDP4BcelrTI3rMXdXF5D )
Example of a node with a HI, HIT, and one RVS:
www.example.com. IN HIP ( 2 200100107B1A74DF365639CC39F1D578
AwEAAbdxyhNuSutc5EMzxTs9LBPCIkOFH8cIvM4p
9+LrV4e19WzK00+CI6zBCQTdtWsuxKbWIy87UOoJTwkUs7lBu+Upr1gsNrut79ryra+bSRGQ
b1slImA8YVJyuIDsj7kwzG7jnERNqnWxZ48AWkskmdHaVDP4BcelrTI3rMXdXF5D
rvs.example.com. )
<span class="grey">Nikander & Laganier Experimental [Page 11]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-12" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
Example of a node with a HI, HIT, and two RVSs:
www.example.com. IN HIP ( 2 200100107B1A74DF365639CC39F1D578
AwEAAbdxyhNuSutc5EMzxTs9LBPCIkOFH8cIvM4p
9+LrV4e19WzK00+CI6zBCQTdtWsuxKbWIy87UOoJTwkUs7lBu+Upr1gsNrut79ryra+bSRGQ
b1slImA8YVJyuIDsj7kwzG7jnERNqnWxZ48AWkskmdHaVDP4BcelrTI3rMXdXF5D
rvs1.example.com.
rvs2.example.com. )
<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. Security Considerations</span>
This section contains a description of the known threats involved
with the usage of the HIP DNS Extension.
In a manner similar to the IPSECKEY RR [<a href="./rfc4025" title=""A Method for Storing IPsec Keying Material in DNS"">RFC4025</a>], the HIP DNS
Extension allows for the provision of two HIP nodes with the public
keying material (HI) of their peer. These HIs will be subsequently
used in a key exchange between the peers. Hence, the HIP DNS
Extension introduces the same kind of threats that IPSECKEY does,
plus threats caused by the possibility given to a HIP node to
initiate or accept a HIP exchange using "opportunistic" or
"unpublished Initiator HI" modes.
A HIP node SHOULD obtain HIP RRs from a trusted party trough a secure
channel ensuring data integrity and authenticity of the RRs. DNSSEC
[<a href="./rfc4033" title=""DNS Security Introduction and Requirements"">RFC4033</a>] [<a href="./rfc4034" title=""Resource Records for the DNS Security Extensions"">RFC4034</a>] [<a href="./rfc4035" title=""Protocol Modifications for the DNS Security Extensions"">RFC4035</a>] provides such a secure channel.
However, it should be emphasized that DNSSEC only offers data
integrity and authenticity guarantees to the channel between the DNS
server publishing a zone and the HIP node. DNSSEC does not ensure
that the entity publishing the zone is trusted. Therefore, the RRSIG
signature of the HIP RRSet MUST NOT be misinterpreted as a
certificate binding the HI and/or the HIT to the owner name.
In the absence of a proper secure channel, both parties are
vulnerable to MitM and DoS attacks, and unrelated parties might be
subject to DoS attacks as well. These threats are described in the
following sections.
<span class="h3"><a class="selflink" id="section-8.1" href="#section-8.1">8.1</a>. Attacker Tampering with an Insecure HIP RR</span>
The HIP RR contains public keying material in the form of the named
peer's public key (the HI) and its secure hash (the HIT). Both of
these are not sensitive to attacks where an adversary gains knowledge
of them. However, an attacker that is able to mount an active attack
on the DNS, i.e., tampers with this HIP RR (e.g., using DNS
spoofing), is able to mount Man-in-the-Middle attacks on the
cryptographic core of the eventual HIP exchange (Responder's HIP RR
rewritten by the attacker).
<span class="grey">Nikander & Laganier Experimental [Page 12]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-13" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
The HIP RR may contain a rendezvous server domain name resolved into
a destination IP address where the named peer is reachable by an I1,
as per the HIP Rendezvous Extension [<a href="./rfc5204" title=""Host Identity Protocol (HIP) Rendezvous Extension"">RFC5204</a>]. Thus, an attacker
able to tamper with this RR is able to redirect I1 packets sent to
the named peer to a chosen IP address for DoS or MitM attacks. Note
that this kind of attack is not specific to HIP and exists
independently of whether or not HIP and the HIP RR are used. Such an
attacker might tamper with A and AAAA RRs as well.
An attacker might obviously use these two attacks in conjunction: It
will replace the Responder's HI and RVS IP address by its own in a
spoofed DNS packet sent to the Initiator HI, then redirect all
exchanged packets to him and mount a MitM on HIP. In this case, HIP
won't provide confidentiality nor Initiator HI protection from
eavesdroppers.
<span class="h3"><a class="selflink" id="section-8.2" href="#section-8.2">8.2</a>. Hash and HITs Collisions</span>
As with many cryptographic algorithms, some secure hashes (e.g.,
SHA1, used by HIP to generate a HIT from an HI) eventually become
insecure, because an exploit has been found in which an attacker with
reasonable computation power breaks one of the security features of
the hash (e.g., its supposed collision resistance). This is why a
HIP end-node implementation SHOULD NOT authenticate its HIP peers
based solely on a HIT retrieved from the DNS, but SHOULD rather use
HI-based authentication.
<span class="h3"><a class="selflink" id="section-8.3" href="#section-8.3">8.3</a>. DNSSEC</span>
In the absence of DNSSEC, the HIP RR is subject to the threats
described in <a href="./rfc3833">RFC 3833</a> [<a href="./rfc3833" title=""Threat Analysis of the Domain Name System (DNS)"">RFC3833</a>].
<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. IANA Considerations</span>
IANA has allocated one new RR type code (55) for the HIP RR from the
standard RR type space.
IANA does not need to open a new registry for public key algorithms
of the HIP RR because the HIP RR reuses "algorithms types" defined
for the IPSECKEY RR [<a href="./rfc4025" title=""A Method for Storing IPsec Keying Material in DNS"">RFC4025</a>]. Presently defined values are shown
here for reference only:
0 is reserved
1 is DSA
2 is RSA
<span class="grey">Nikander & Laganier Experimental [Page 13]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-14" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
In the future, if a new algorithm is to be used for the HIP RR, a new
algorithm type and corresponding public key encoding should be
defined for the IPSECKEY RR. The HIP RR should reuse both the same
algorithm type and the same corresponding public key format as the
IPSECKEY RR.
<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>. Acknowledgments</span>
As usual in the IETF, this document is the result of a collaboration
between many people. The authors would like to thank the author
(Michael Richardson), contributors, and reviewers of the IPSECKEY RR
[<a href="./rfc4025" title=""A Method for Storing IPsec Keying Material in DNS"">RFC4025</a>] specification, after which this document was framed. The
authors would also like to thank the following people, who have
provided thoughtful and helpful discussions and/or suggestions, that
have helped improve this document: Jeff Ahrenholz, Rob Austein, Hannu
Flinck, Olafur Gudmundsson, Tom Henderson, Peter Koch, Olaf Kolkman,
Miika Komu, Andrew McGregor, Erik Nordmark, and Gabriel Montenegro.
Some parts of this document stem from the HIP specification
[<a href="./rfc5201" title=""Host Identity Protocol"">RFC5201</a>].
<span class="h2"><a class="selflink" id="section-11" href="#section-11">11</a>. References</span>
<span class="h3"><a class="selflink" id="section-11.1" href="#section-11.1">11.1</a>. Normative references</span>
[<a id="ref-RFC1034">RFC1034</a>] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, <a href="./rfc1034">RFC 1034</a>, November 1987.
[<a id="ref-RFC1035">RFC1035</a>] Mockapetris, P., "Domain names - implementation and
specification", STD 13, <a href="./rfc1035">RFC 1035</a>, November 1987.
[<a id="ref-RFC2119">RFC2119</a>] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.
[<a id="ref-RFC2181">RFC2181</a>] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", <a href="./rfc2181">RFC 2181</a>, July 1997.
[<a id="ref-RFC3596">RFC3596</a>] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", <a href="./rfc3596">RFC 3596</a>,
October 2003.
[<a id="ref-RFC4025">RFC4025</a>] Richardson, M., "A Method for Storing IPsec Keying
Material in DNS", <a href="./rfc4025">RFC 4025</a>, March 2005.
[<a id="ref-RFC4033">RFC4033</a>] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
<a href="./rfc4033">RFC 4033</a>, March 2005.
<span class="grey">Nikander & Laganier Experimental [Page 14]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-15" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
[<a id="ref-RFC4034">RFC4034</a>] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
<a href="./rfc4034">RFC 4034</a>, March 2005.
[<a id="ref-RFC4035">RFC4035</a>] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", <a href="./rfc4035">RFC 4035</a>, March 2005.
[<a id="ref-RFC4648">RFC4648</a>] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", <a href="./rfc4648">RFC 4648</a>, October 2006.
[<a id="ref-RFC5201">RFC5201</a>] Moskowitz, R., Nikander, P., Jokela, P., Ed., and T.
Henderson, "Host Identity Protocol", <a href="./rfc5201">RFC 5201</a>, April 2008.
[<a id="ref-RFC5204">RFC5204</a>] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
Rendezvous Extension", <a href="./rfc5204">RFC 5204</a>, April 2008.
<span class="h3"><a class="selflink" id="section-11.2" href="#section-11.2">11.2</a>. Informative references</span>
[<a id="ref-RFC2536">RFC2536</a>] Eastlake, D., "DSA KEYs and SIGs in the Domain Name System
(DNS)", <a href="./rfc2536">RFC 2536</a>, March 1999.
[<a id="ref-RFC3110">RFC3110</a>] Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain
Name System (DNS)", <a href="./rfc3110">RFC 3110</a>, May 2001.
[<a id="ref-RFC3833">RFC3833</a>] Atkins, D. and R. Austein, "Threat Analysis of the Domain
Name System (DNS)", <a href="./rfc3833">RFC 3833</a>, August 2004.
[<a id="ref-RFC4423">RFC4423</a>] Moskowitz, R. and P. Nikander, "Host Identity Protocol
(HIP) Architecture", <a href="./rfc4423">RFC 4423</a>, May 2006.
[<a id="ref-RFC5206">RFC5206</a>] Henderson, T., Ed., "End-Host Mobility and Multihoming
with the Host Identity Protocol", <a href="./rfc5206">RFC 5206</a>, April 2008.
<span class="grey">Nikander & Laganier Experimental [Page 15]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-16" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
Authors' Addresses
Pekka Nikander
Ericsson Research NomadicLab
JORVAS FIN-02420
FINLAND
Phone: +358 9 299 1
EMail: pekka.nikander@nomadiclab.com
Julien Laganier
DoCoMo Communications Laboratories Europe GmbH
Landsberger Strasse 312
Munich 80687
Germany
Phone: +49 89 56824 231
EMail: julien.ietf@laposte.net
URI: <a href="http://www.docomolab-euro.com/">http://www.docomolab-euro.com/</a>
<span class="grey">Nikander & Laganier Experimental [Page 16]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-17" ></span>
<span class="grey"><a href="./rfc5205">RFC 5205</a> HIP DNS Extension April 2008</span>
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a>, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and <a href="https://www.rfc-editor.org/bcp/bcp79">BCP 79</a>.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
<a href="http://www.ietf.org/ipr">http://www.ietf.org/ipr</a>.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Nikander & Laganier Experimental [Page 17]
</pre>
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