Limiting the Scope of the KEY Resource Record (RR)
RFC 3445
| Document | Type |
RFC
- Proposed Standard
(December 2002)
Errata
Updates RFC 2535
|
|
|---|---|---|---|
| Authors | Scott Rose , Dan Massey | ||
| Last updated | 2020-01-21 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| IESG | Responsible AD | Erik Nordmark | |
| Send notices to | (None) |
RFC 3445
Network Working Group D. Massey
Request for Comments: 3445 USC/ISI
Updates: 2535 S. Rose
Category: Standards Track NIST
December 2002
Limiting the Scope of the KEY Resource Record (RR)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document limits the Domain Name System (DNS) KEY Resource Record
(RR) to only keys used by the Domain Name System Security Extensions
(DNSSEC). The original KEY RR used sub-typing to store both DNSSEC
keys and arbitrary application keys. Storing both DNSSEC and
application keys with the same record type is a mistake. This
document removes application keys from the KEY record by redefining
the Protocol Octet field in the KEY RR Data. As a result of removing
application keys, all but one of the flags in the KEY record become
unnecessary and are redefined. Three existing application key sub-
types are changed to reserved, but the format of the KEY record is
not changed. This document updates RFC 2535.
1. Introduction
This document limits the scope of the KEY Resource Record (RR). The
KEY RR was defined in [3] and used resource record sub-typing to hold
arbitrary public keys such as Email, IPSEC, DNSSEC, and TLS keys.
This document eliminates the existing Email, IPSEC, and TLS sub-types
and prohibits the introduction of new sub-types. DNSSEC will be the
only allowable sub-type for the KEY RR (hence sub-typing is
essentially eliminated) and all but one of the KEY RR flags are also
eliminated.
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RFC 3445 Limiting the KEY Resource Record (RR) December 2002
Section 2 presents the motivation for restricting the KEY record and
Section 3 defines the revised KEY RR. Sections 4 and 5 summarize the
changes from RFC 2535 and discuss backwards compatibility. It is
important to note that this document restricts the use of the KEY RR
and simplifies the flags, but does not change the definition or use
of DNSSEC keys.
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 [1].
2. Motivation for Restricting the KEY RR
The KEY RR RDATA [3] consists of Flags, a Protocol Octet, an
Algorithm type, and a Public Key. The Protocol Octet identifies the
KEY RR sub-type. DNSSEC public keys are stored in the KEY RR using a
Protocol Octet value of 3. Email, IPSEC, and TLS keys were also
stored in the KEY RR and used Protocol Octet values of 1,2, and 4
(respectively). Protocol Octet values 5-254 were available for
assignment by IANA and values were requested (but not assigned) for
applications such as SSH.
Any use of sub-typing has inherent limitations. A resolver can not
specify the desired sub-type in a DNS query and most DNS operations
apply only to resource records sets. For example, a resolver can not
directly request the DNSSEC subtype KEY RRs. Instead, the resolver
has to request all KEY RRs associated with a DNS name and then search
the set for the desired DNSSEC sub-type. DNSSEC signatures also
apply to the set of all KEY RRs associated with the DNS name,
regardless of sub-type.
In the case of the KEY RR, the inherent sub-type limitations are
exacerbated since the sub-type is used to distinguish between DNSSEC
keys and application keys. DNSSEC keys and application keys differ
in virtually every respect and Section 2.1 discusses these
differences in more detail. Combining these very different types of
keys into a single sub-typed resource record adds unnecessary
complexity and increases the potential for implementation and
deployment errors. Limited experimental deployment has shown that
application keys stored in KEY RRs are problematic.
This document addresses these issues by removing all application keys
from the KEY RR. Note that the scope of this document is strictly
limited to the KEY RR and this document does not endorse or restrict
the storage of application keys in other, yet undefined, resource
records.
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RFC 3445 Limiting the KEY Resource Record (RR) December 2002
2.1 Differences Between DNSSEC and Application Keys
DNSSEC keys are an essential part of the DNSSEC protocol and are used
by both name servers and resolvers in order to perform DNS tasks. A
DNS zone key, used to sign and authenticate RR sets, is the most
common example of a DNSSEC key. SIG(0) [4] and TKEY [3] also use
DNSSEC keys.
Application keys such as Email keys, IPSEC keys, and TLS keys are
simply another type of data. These keys have no special meaning to a
name server or resolver.
The following table summarizes some of the differences between DNSSEC
keys and application keys:
1. They serve different purposes.
2. They are managed by different administrators.
3. They are authenticated according to different rules.
4. Nameservers use different rules when including them in
responses.
5. Resolvers process them in different ways.
6. Faults/key compromises have different consequences.
1. The purpose of a DNSSEC key is to sign resource records
associated with a DNS zone (or generate DNS transaction signatures in
the case of SIG(0)/TKEY). But the purpose of an application key is
specific to the application. Application keys, such as PGP/email,
IPSEC, TLS, and SSH keys, are not a mandatory part of any zone and
the purpose and proper use of application keys is outside the scope
of DNS.
2. DNSSEC keys are managed by DNS administrators, but application
keys are managed by application administrators. The DNS zone
administrator determines the key lifetime, handles any suspected key
compromises, and manages any DNSSEC key changes. Likewise, the
application administrator is responsible for the same functions for
the application keys related to the application. For example, a user
typically manages her own PGP key and a server manages its own TLS
key. Application key management tasks are outside the scope of DNS
administration.
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RFC 3445 Limiting the KEY Resource Record (RR) December 2002
3. Client Network-Layer Model
The packet PW appears as a single point-to-point link to the client
layer. Network-layer adjacency formation and maintenance between the
client equipments will follow the normal practice needed to support
the required relationship in the client layer. The assignment of
metrics for this point-to-point link is a matter for the client
layer. In a hop-by-hop routing network, the metrics would normally
be assigned by appropriate configuration of the embedded client
network-layer equipment (e.g., the embedded client LSR). Where the
client was using the packet PW as part of a traffic-engineered path,
it is up to the operator of the client network to ensure that the
server-layer operator provides the necessary service-level agreement.
4. Forwarding Model
The packet PW forwarding model is illustrated in Figure 2. The
forwarding operation can be likened to a virtual private network
(VPN), in which a forwarding decision is first taken at the client
layer, an encapsulation is applied, and then a second forwarding
decision is taken at the server layer.
+------------------------------------------------+
| |
| +--------+ +--------+ |
| | | Pkt +-----+ | | |
------+ +---------+ PW1 +--------+ +------
| | Client | AC +-----+ | Server | |
Client | | LSR | | LSR | | Server
Network | | | Pkt +-----+ | | | Network
------+ +---------+ PW2 +--------+ +------
| | | AC +-----+ | | |
| +--------+ +--------+ |
| |
+------------------------------------------------+
Figure 2: Packet PW Forwarding Model
A packet PW PE comprises three components: the client LSR, a PW
processor, and a server LSR. Note that [RFC3985] does not formally
indicate the presence of the server LSR because it does not concern
itself with the server layer. However it is useful in this document
to recognize that the server LSR exists.
It may be useful to first recall the operation of a layer 2 PW such
as an Ethernet PW [RFC4448] within this model. The client LSR is not
present, and packets arrive directly on the attachment circuit (AC)
that is part of the client network. The PW function undertakes any
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header processing, if configured to do so; it then optionally pushes
the PW control word (CW) and finally pushes the PW label. The PW
function then passes the packet to the LSR function, which pushes the
label needed to reach the egress PE and forwards the packet to the
next hop in the server network. At the egress PE, the packet
typically arrives with the PW label at the top of the stack; the
packet is thus directed to the correct PW instance. The PW instance
performs any required reconstruction using, if necessary, the CW, and
the packet is sent directly to the attachment circuit.
Now let us consider the case of client-layer MPLS traffic being
carried over a packet PW. An LSR belonging to the client layer is
embedded within the PE equipment. This is a type of native service
processing element [RFC3985]. The client LSR determines the next hop
in the client layer, and pushes the label needed by the next hop in
the client layer. It then encapsulates the packet in an Ethernet
header setting the Ethertype to MPLS, and the client LSR passes the
packet to the correct PW instance. The PW instance then proceeds as
defined for an Ethernet PW [RFC4448] by optionally pushing the
control word, then pushing the PW label, and finally handing the
packet to the server-layer LSR for delivery to the egress PE in the
server layer.
At the egress PE in the server layer, the packet is first processed
by the server LSR, which uses the PW label to pass the packet to the
correct PW instance. This PW instance processes the packet as
described in [RFC4448]. The resultant Ethernet encapsulated client
packet is then passed to the egress client LSR, which then processes
the packet in the normal manner.
Note that although the description above is written in terms of the
behavior of an MPLS LSR, the processing model would be similar for an
IP packet or any other protocol type.
Note that the semantics of the PW between the client LSRs is a point-
to-point link.
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5. Packet PW Encapsulation
The client network-layer packet encapsulation into a packet PW is
shown in Figure 3.
+-------------------------------+
| Client |
| Network-Layer |
| Packet | n octets
| |
+-------------------------------+
| |
| Ethernet | 14 octets
| Header |
| +---------------+
| |
+---------------+---------------+
| Optional Control Word | 4 octets
+-------------------------------+
| PW Label | 4 octets
+-------------------------------+
| Server MPLS Tunnel Label(s) | n*4 octets (4 octets per label)
+-------------------------------+
Figure 3: Packet PW Encapsulation
This conforms to the PW protocols stack as defined in [RFC4448]. The
protocol stack is unremarkable except to note that the stack does not
retain 32-bit alignment between the virtual Ethernet header and the
PW optional control word (or the PW label when the optional
components are not present in the PW header). This loss of 32 bits
of alignment is necessary to preserve backwards compatibility with
the Ethernet PW design [RFC4448]
Ethernet Raw Mode (PW type 5) MUST be used for the packet PW.
The PEs MAY use a local Ethernet address for the Ethernet header used
to encapsulate the client network-layer packet or MAY use the special
Ethernet addresses "PacketPWEthA" or "PacketPWEthB" as described
below.
IANA has allocated two unicast Ethernet addresses [RFC5342] for use
with this protocol, referred to as "PacketPWEthA" and "PacketPWEthB".
Where [RFC4447] signaling is used to set up the PW, the LDP peers
numerically compare their IP addresses. The LDP PE with the higher-
value IP address will use PacketPWEthA, whilst the LDP peer with the
lower-value IP address uses PacketPWEthB.
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Where no signaling PW protocol is used, suitable Ethernet addresses
MUST be configured at each PE.
Although this PW represents a point-to-point connection, the use of a
multicast destination address in the Ethernet encapsulation is
REQUIRED by some client-layer protocols. Peers MUST be prepared to
handle a multicast destination address in the Ethernet encapsulation.
6. Ethernet and IEEE 802.1 Functional Restrictions
The use of Ethernet as the encapsulation mechanism for traffic
between the server LSRs is a convenience based on the widespread
availability of existing hardware. In this application, there is no
requirement for any Ethernet feature other than its protocol
multiplexing capability. Thus, for example, a server LSR is not
required to implement the Ethernet OAM.
The use and applicability of VLANs, IEEE 802.1p, and IEEE 802.1Q
tagging between PEs is not supported.
Point-to-multipoint and multipoint-to-multipoint operation of the
virtual Ethernet is not supported.
7. Congestion Considerations
A packet pseudowire is normally used to carry IP, MPLS and their
associated support protocols over an MPLS network. There are no
congestion considerations beyond those that ordinarily apply to an IP
or MPLS network. Where the packet protocol being carried is not IP
or MPLS and the traffic volumes are greater than that ordinarily
associated with the support protocols in an IP or MPLS network, the
congestion considerations developed for PWs apply [RFC3985]
[RFC5659].
8. Security Considerations
The virtual Ethernet approach to packet PW introduces no new security
risks. A more detailed discussion of pseudowire security is given in
[RFC3985], [RFC4447], and [RFC3916].
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9. IANA Considerations
IANA has allocated two Ethernet unicast addresses from "IANA Unicast
48-bit MAC Addresses".
Address Usage Reference
------------------- ---------------- ---------
00-00-5E-00-52-00 PacketPWEthA [RFC6658]
00-00-5E-00-52-01 PacketPWEthB [RFC6658]
10. Acknowledgements
The authors acknowledge the contributions made to this document by
Sami Boutros, Giles Herron, Siva Sivabalan, and David Ward.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
Heron, "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC4448] Martini, L., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, April 2006.
[RFC5342] Eastlake, D., "IANA Considerations and IETF Protocol Usage
for IEEE 802 Parameters", BCP 141, RFC 5342,
September 2008.
11.2. Informative References
[IEEE.802.1AB.2009]
Institute of Electrical and Electronics Engineers, "IEEE
Standard for Local and Metropolitan Area Networks --
Station and Media Access Control Connectivity Discovery",
IEEE Standard 802.1AB, 2009.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3916] Xiao, X., McPherson, D., and P. Pate, "Requirements for
Pseudo-Wire Emulation Edge-to-Edge (PWE3)", RFC 3916,
September 2004.
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[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, February 2006.
[RFC5317] Bryant, S. and L. Andersson, "Joint Working Team (JWT)
Report on MPLS Architectural Considerations for a
Transport Profile", RFC 5317, February 2009.
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-
Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
October 2009.
[RFC5921] Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
Berger, "A Framework for MPLS in Transport Networks",
RFC 5921, July 2010.
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Appendix A. Encapsulation Approaches Considered
A number of approaches to the design of a packet pseudowire (PW) were
investigated by the PWE3 Working Group and were discussed in IETF
meetings and on the PWE3 list. This section describes the approaches
that were analyzed and the technical issues that the authors took
into consideration in arriving at the approach described in the main
body of this document. This appendix is provided so that engineers
considering alternative optimizations can have access to the
rationale for the selection of the approach described in this
document.
In a typical network, there are usually no more that four network-
layer protocols that need to be supported: IPv4, IPv6, MPLS, and
Connectionless Network Service (CLNS). However, any solution needs
to be scalable to a larger number of protocols. The approaches
considered in this appendix all satisfy this minimum requirement but
vary in their ability to support larger numbers of network-layer
protocols.
Additionally, it is beneficial if the complete set of protocols
carried over the network in support of a set of CE peers fate share.
It is additionally beneficial if a single OAM session can be used to
monitor the behavior of this complete set. During the investigation,
various views were expressed as to where these benefits lay on the
scale from absolutely required to "nice to have", but in the end,
they were not a factor in reaching our conclusion.
Four candidate approaches were analyzed:
1. A protocol identifier (PID) in the PW control word (CW)
2. A PID label
3. Parallel PWs - one per protocol
4. Virtual Ethernet
A.1. A Protocol Identifier in the Control Word
In this approach, a Protocol Identifier (PID) is included in the PW
control word (CW) by appending it to the generic control word
[RFC4385] to make a 6-byte CW (it was thought that this approach
would include 2 reserved bytes to provide 32-bit alignment, but then
this was optimized out). A variant of this is just to use a 2-byte
PID without a control word.
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This is a simple approach and is basically a virtual PPP interface
without the PPP control protocol. This has a smaller MTU than, for
example, a virtual Ethernet would need; however, in forwarding terms,
it is not as simple as the PID label or multiple PW approaches
described next and may not be deployable on a number of existing
hardware platforms.
A.2. PID Label
In this approach, the PID is indicated by including a label after the
PW label that indicates the protocol type, as shown in Figure 4.
+-------------------------------+
| Client |
| Network-Layer |
| Packet | n octets
| |
+-------------------------------+
| Optional Control Word | 4 octets
+-------------------------------+
| PID Label (S=1) | 4 octets
+-------------------------------+
| PW Label | 4 octets
+-------------------------------+
| Server MPLS Tunnel Label(s) | n*4 octets (four octets per label)
+-------------------------------+
Figure 4: Encapsulation of a Pseudowire with
a Pseudowire Load-Balancing Label
In the PID label approach, a new Label Distribution Protocol (LDP)
Forwarding Equivalence Class (FEC) element is used to signal the
mapping between protocol type and the PID label. This approach
complies with [RFC3031].
A similar approach to PID label is described in Section 3.4.5 of
[RFC5921]. In this case, when the client is a network-layer packet
service such as IP or MPLS, a service label and demultiplexer label
(which may be combined) are used to provide the necessary
identifications needed to carry this traffic over an LSP.
The authors surveyed the hardware designs produced by a number of
companies across the industry and concluded that whilst the approach
complies with the MPLS architecture, it may conflict with a number of
designers' interpretations of the existing MPLS architecture. This
led to concerns that the approach may result in unexpected
difficulties in the future. Specifically, there was an assumption in
many designs that a forwarding decision should be made on the basis
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of a single label. Whilst the approach is attractive, it cannot be
supported by many commodity chip sets, and this would require new
hardware, which would increase the cost of deployment and delay the
introduction of a packet PW service.
A.3. Parallel PWs
In this approach, one PW is constructed for each protocol type that
must be carried between the PEs. Thus, a complete packet PW would
consist of a bundle of PWs. This model would be very simple and
efficient from a forwarding point of view. The number of parallel
PWs required would normally be relatively small. In a typical
network, there are usually no more that four network-layer protocols
that need to be supported: IPv4, IPv6, MPLS, and CLNS. However, any
solution needs to be scalable to a larger number of protocols.
There are a number of serious downsides with this approach:
1. From an operational point of view, the lack of fate sharing
between the protocol types can lead to complex faults that are
difficult to diagnose.
2. There is an undesirable trade-off in the OAM related to the first
point. We would have to run an OAM on each PW and bind them
together, which leads to significant protocol and software
complexity and does not scale well. Alternatively, we would need
to run a single OAM session on one of the PWs as a proxy for the
others and then diagnose any more complex failures on a case-by-
case basis. To some extent, the issue of fate sharing between
protocols in the bundle (for example, the assumed fate sharing
between CLNS and IP in IS-IS) can be mitigated through the use of
Bidirectional Forwarding Detection (BFD).
3. The need to configure, manage, and synchronize the behavior of a
group of PWs as if they were a single PW leads to an increase in
control-plane complexity.
The Parallel PW mechanism is therefore an approach that simplifies
the forwarding plane, but only at a cost of a considerable increase
in other aspects of the design, in particular, operation of the PW.
A.4. Virtual Ethernet
Using a virtual Ethernet to provide a packet PW would require PEs to
include a virtual (internal) Ethernet interface and then to use an
Ethernet PW [RFC4448] to carry the user traffic. This is
conceptually simple and can be implemented today without any further
standards action, although there are a number of applicability
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3. DNSSEC zone keys are used to authenticate application keys, but
by definition, application keys are not allowed to authenticate DNS
zone keys. A DNS zone key is either configured as a trusted key or
authenticated by constructing a chain of trust in the DNS hierarchy.
To participate in the chain of trust, a DNS zone needs to exchange
zone key information with its parent zone [3]. Application keys are
not configured as trusted keys in the DNS and are never part of any
DNS chain of trust. Application key data is not needed by the parent
and does not need to be exchanged with the parent zone for secure DNS
resolution to work. A resolver considers an application key RRset as
authenticated DNS information if it has a valid signature from the
local DNS zone keys, but applications could impose additional
security requirements before the application key is accepted as
authentic for use with the application.
4. It may be useful for nameservers to include DNS zone keys in the
additional section of a response, but application keys are typically
not useful unless they have been specifically requested. For
example, it could be useful to include the example.com zone key along
with a response that contains the www.example.com A record and SIG
record. A secure resolver will need the example.com zone key in
order to check the SIG and authenticate the www.example.com A record.
It is typically not useful to include the IPSEC, email, and TLS keys
along with the A record. Note that by placing application keys in
the KEY record, a resolver would need the IPSEC, email, TLS, and
other key associated with example.com if the resolver intends to
authenticate the example.com zone key (since signatures only apply to
the entire KEY RR set). Depending on the number of protocols
involved, the KEY RR set could grow unwieldy for resolvers, and DNS
administrators to manage.
5. DNS zone keys require special handling by resolvers, but
application keys are treated the same as any other type of DNS data.
The DNSSEC keys are of no value to end applications, unless the
applications plan to do their own DNS authentication. By definition,
secure resolvers are not allowed to use application keys as part of
the authentication process. Application keys have no unique meaning
to resolvers and are only useful to the application requesting the
key. Note that if sub-types are used to identify the application
key, then either the interface to the resolver needs to specify the
sub-type or the application needs to be able to accept all KEY RRs
and pick out the desired sub-type.
6. A fault or compromise of a DNS zone key can lead to invalid or
forged DNS data, but a fault or compromise of an application key
should have no impact on other DNS data. Incorrectly adding or
changing a DNS zone key can invalidate all of the DNS data in the
zone and in all of its subzones. By using a compromised key, an
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RFC 3445 Limiting the KEY Resource Record (RR) December 2002
attacker can forge data from the effected zone and for any of its
sub-zones. A fault or compromise of an application key has
implications for that application, but it should not have an impact
on the DNS. Note that application key faults and key compromises can
have an impact on the entire DNS if the application key and DNS zone
keys are both stored in the KEY RR.
In summary, DNSSEC keys and application keys differ in most every
respect. DNSSEC keys are an essential part of the DNS infrastructure
and require special handling by DNS administrators and DNS resolvers.
Application keys are simply another type of data and have no special
meaning to DNS administrators or resolvers. These two different
types of data do not belong in the same resource record.
3. Definition of the KEY RR
The KEY RR uses type 25 and is used as resource record for storing
DNSSEC keys. The RDATA for a KEY RR consists of flags, a protocol
octet, the algorithm number octet, and the public key itself. The
format is as follows:
---------------------------------------------------------------------
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flags | protocol | algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| /
/ public key /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
KEY RR Format
---------------------------------------------------------------------
In the flags field, all bits except bit 7 are reserved and MUST be
zero. If Bit 7 (Zone bit) is set to 1, then the KEY is a DNS Zone
key. If Bit 7 is set to 0, the KEY is not a zone key. SIG(0)/TKEY
are examples of DNSSEC keys that are not zone keys.
The protocol field MUST be set to 3.
The algorithm and public key fields are not changed.
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RFC 3445 Limiting the KEY Resource Record (RR) December 2002
4. Changes from RFC 2535 KEY RR
The KEY RDATA format is not changed.
All flags except for the zone key flag are eliminated:
The A/C bits (bits 0 and 1) are eliminated. They MUST be set to 0
and MUST be ignored by the receiver.
The extended flags bit (bit 3) is eliminated. It MUST be set to 0
and MUST be ignored by the receiver.
The host/user bit (bit 6) is eliminated. It MUST be set to 0 and
MUST be ignored by the receiver.
The zone bit (bit 7) remains unchanged.
The signatory field (bits 12-15) are eliminated by [5]. They MUST
be set to 0 and MUST be ignored by the receiver.
Bits 2,4,5,8,9,10,11 remain unchanged. They are reserved, MUST be
set to zero and MUST be ignored by the receiver.
Assignment of any future KEY RR Flag values requires a standards
action.
All Protocol Octet values except DNSSEC (3) are eliminated:
Value 1 (Email) is renamed to RESERVED.
Value 2 (IPSEC) is renamed to RESERVED.
Value 3 (DNSSEC) is unchanged.
Value 4 (TLS) is renamed to RESERVED.
Value 5-254 remains unchanged (reserved).
Value 255 (ANY) is renamed to RESERVED.
The authoritative data for a zone MUST NOT include any KEY records
with a protocol octet other than 3. The registry maintained by IANA
for protocol values is closed for new assignments.
Name servers and resolvers SHOULD accept KEY RR sets that contain KEY
RRs with a value other than 3. If out of date DNS zones contain
deprecated KEY RRs with a protocol octet value other than 3, then
simply dropping the deprecated KEY RRs from the KEY RR set would
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RFC 3445 Limiting the KEY Resource Record (RR) December 2002
invalidate any associated SIG record(s) and could create caching
consistency problems. Note that KEY RRs with a protocol octet value
other than 3 MUST NOT be used to authenticate DNS data.
The algorithm and public key fields are not changed.
5. Backward Compatibility
DNSSEC zone KEY RRs are not changed and remain backwards compatible.
A properly formatted RFC 2535 zone KEY would have all flag bits,
other than the Zone Bit (Bit 7), set to 0 and would have the Protocol
Octet set to 3. This remains true under the restricted KEY.
DNSSEC non-zone KEY RRs (SIG(0)/TKEY keys) are backwards compatible,
but the distinction between host and user keys (flag bit 6) is lost.
No backwards compatibility is provided for application keys. Any
Email, IPSEC, or TLS keys are now deprecated. Storing application
keys in the KEY RR created problems such as keys at the apex and
large RR sets and some change in the definition and/or usage of the
KEY RR would have been required even if the approach described here
were not adopted.
Overall, existing nameservers and resolvers will continue to
correctly process KEY RRs with a sub-type of DNSSEC keys.
6. Storing Application Keys in the DNS
The scope of this document is strictly limited to the KEY record.
This document prohibits storing application keys in the KEY record,
but it does not endorse or restrict the storing application keys in
other record types. Other documents can describe how DNS handles
application keys.
7. IANA Considerations
RFC 2535 created an IANA registry for DNS KEY RR Protocol Octet
values. Values 1, 2, 3, 4, and 255 were assigned by RFC 2535 and
values 5-254 were made available for assignment by IANA. This
document makes two sets of changes to this registry.
First, this document re-assigns DNS KEY RR Protocol Octet values 1,
2, 4, and 255 to "reserved". DNS Key RR Protocol Octet Value 3
remains unchanged as "DNSSEC".
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RFC 3445 Limiting the KEY Resource Record (RR) December 2002
Second, new values are no longer available for assignment by IANA and
this document closes the IANA registry for DNS KEY RR Protocol Octet
Values. Assignment of any future KEY RR Protocol Octet values
requires a standards action.
8. Security Considerations
This document eliminates potential security problems that could arise
due to the coupling of DNS zone keys and application keys. Prior to
the change described in this document, a correctly authenticated KEY
set could include both application keys and DNSSEC keys. This
document restricts the KEY RR to DNS security usage only. This is an
attempt to simplify the security model and make it less user-error
prone. If one of the application keys is compromised, it could be
used as a false zone key to create false DNS signatures (SIG
records). Resolvers that do not carefully check the KEY sub-type
could believe these false signatures and incorrectly authenticate DNS
data. With this change, application keys cannot appear in an
authenticated KEY set and this vulnerability is eliminated.
The format and correct usage of DNSSEC keys is not changed by this
document and no new security considerations are introduced.
9. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[3] Eastlake, D., "Secret Key Establishment for DNS (TKEY RR)", RFC
2930, September 2000.
[4] Eastlake, D., "DNS Request and Transaction Signatures
(SIG(0)s)", RFC 2931, September 2000.
[5] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, November 2000.
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RFC 3445 Limiting the KEY Resource Record (RR) December 2002
10. Authors' Addresses
Dan Massey
USC Information Sciences Institute
3811 N. Fairfax Drive
Arlington, VA 22203
USA
EMail: masseyd@isi.edu
Scott Rose
National Institute for Standards and Technology
100 Bureau Drive
Gaithersburg, MD 20899-3460
USA
EMail: scott.rose@nist.gov
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RFC 3445 Limiting the KEY Resource Record (RR) December 2002
11. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS 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.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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