draft-ietf-dnsext-restrict-key-for-dnssec-04.txt   rfc3445.txt 
DNS Extensions D. Massey Network Working Group D. Massey
Internet-Draft USC/ISI Request for Comments: 3445 USC/ISI
Expires: March 11, 2003 S. Rose Updates: 2535 S. Rose
NIST Category: Standards Track NIST
September 10, 2002 December 2002
Limiting the Scope of the KEY Resource Record
out
draft-ietf-dnsext-restrict-key-for-dnssec-04.txt Limiting the Scope of the KEY Resource Record (RR)
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved. Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract Abstract
This document limits the Domain Name System KEY resource record to This document limits the Domain Name System (DNS) KEY Resource Record
only keys used by the Domain Name System Security Extensions (RR) to only keys used by the Domain Name System Security Extensions
(DNSSEC). The original KEY resource record used sub-typing to store (DNSSEC). The original KEY RR used sub-typing to store both DNSSEC
both DNSSEC keys and arbitrary application keys. Storing both DNSSEC keys and arbitrary application keys. Storing both DNSSEC and
and application keys with the same record type is a mistake. This application keys with the same record type is a mistake. This
document removes application keys from the KEY record by redefining document removes application keys from the KEY record by redefining
the Protocol Octet field in the KEY Resource Record Data. As a the Protocol Octet field in the KEY RR Data. As a result of removing
result of removing application keys, all but one of the flags in the application keys, all but one of the flags in the KEY record become
KEY record become unnecessary and are redefined. Three existing unnecessary and are redefined. Three existing application key sub-
application key sub-types are changed to reserved, but the format of types are changed to reserved, but the format of the KEY record is
the KEY record is not changed. This document updates RFC 2535. not changed. This document updates RFC 2535.
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].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation for Restricting the KEY RR . . . . . . . . . . . . 4
2.1 Differences Between DNSSEC and Application Keys . . . . . . . 4
3. Definition of the KEY Resource Record . . . . . . . . . . . . 7
4. Changes from RFC 2535 KEY RR . . . . . . . . . . . . . . . . . 8
5. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 10
6. Storing Application Keys in the DNS . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
This document limits the scope of the KEY resource record. The KEY This document limits the scope of the KEY Resource Record (RR). The
resource record was defined in [3] and used resource record sub- KEY RR was defined in [3] and used resource record sub-typing to hold
typing to hold arbitrary public keys such as Email, IPSEC, DNSSEC, arbitrary public keys such as Email, IPSEC, DNSSEC, and TLS keys.
and TLS keys. This document eliminates the existing Email, IPSEC, This document eliminates the existing Email, IPSEC, and TLS sub-types
and TLS sub-types and prohibits the introduction of new sub-types. and prohibits the introduction of new sub-types. DNSSEC will be the
DNSSEC will be the only allowable sub-type for the KEY RR (hence sub- only allowable sub-type for the KEY RR (hence sub-typing is
typing is essentially eliminated) and all but one of the KEY RR flags essentially eliminated) and all but one of the KEY RR flags are also
are also eliminated. eliminated.
Section 2 presents the motivation for restricting the KEY record and Section 2 presents the motivation for restricting the KEY record and
Section 3 defines the revised KEY RR. Sections 4 and 5 summarize the Section 3 defines the revised KEY RR. Sections 4 and 5 summarize the
changes from RFC 2535 and discuss backwards compatibility. It is changes from RFC 2535 and discuss backwards compatibility. It is
important to note that this document restricts the use of the KEY RR 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 and simplifies the flags, but does not change the definition or use
of DNSSEC keys. 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 2. Motivation for Restricting the KEY RR
The KEY RR RDATA [3] consists of Flags, a Protocol Octet, an The KEY RR RDATA [3] consists of Flags, a Protocol Octet, an
Algorithm type, and a Public Key. The Protocol Octet identifies the 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 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 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 stored in the KEY RR and used Protocol Octet values of 1,2, and 4
(respectively). Protocol Octet values 5-254 were available for (respectively). Protocol Octet values 5-254 were available for
assignment by IANA and values were requested (but not assigned) for assignment by IANA and values were requested (but not assigned) for
applications such as SSH. applications such as SSH.
Any use of sub-typing has inherent limitations. A resolver can not 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 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 apply only to resource records sets. For example, a resolver can not
directly request the DNSSEC subtype KEY RRs. Instead, the resolver directly request the DNSSEC subtype KEY RRs. Instead, the resolver
has to request all KEY RRs associated with a DNS name and then search 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 the set for the desired DNSSEC sub-type. DNSSEC signatures also
apply to the set of all KEY resource records associated with the DNS apply to the set of all KEY RRs associated with the DNS name,
name, regardless of sub-type. regardless of sub-type.
In the case of the KEY RR, the inherent sub-type limitations are In the case of the KEY RR, the inherent sub-type limitations are
exacerbated since the sub-type is used to distinguish between DNSSEC exacerbated since the sub-type is used to distinguish between DNSSEC
keys and application keys. DNSSEC keys and application keys differ keys and application keys. DNSSEC keys and application keys differ
in virtually every respect and Section 2.1 discusses these in virtually every respect and Section 2.1 discusses these
differences in more detail. Combining these very different types of differences in more detail. Combining these very different types of
keys into a single sub-typed resource record adds unnecessary keys into a single sub-typed resource record adds unnecessary
complexity and increases the potential for implementation and complexity and increases the potential for implementation and
deployment errors. Limited experimental deployment has shown that deployment errors. Limited experimental deployment has shown that
application keys stored in KEY RRs are problematic. application keys stored in KEY RRs are problematic.
This document addresses these issues by removing all application keys This document addresses these issues by removing all application keys
from the KEY resource record. Note that the scope of this document from the KEY RR. Note that the scope of this document is strictly
is strictly limited to the KEY RR and this document does not endorse limited to the KEY RR and this document does not endorse or restrict
or restrict the storage of application keys in other, yet undefined, the storage of application keys in other, yet undefined, resource
resource records. records.
2.1 Differences Between DNSSEC and Application Keys 2.1 Differences Between DNSSEC and Application Keys
DNSSEC keys are an essential part of the DNSSEC protocol and are used 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 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 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 common example of a DNSSEC key. SIG(0) [4] and TKEY [3] also use
DNSSEC keys. DNSSEC keys.
Application keys such as Email keys, IPSEC keys, and TLS keys are Application keys such as Email keys, IPSEC keys, and TLS keys are
simply another type data. These keys have no special meaning to a simply another type of data. These keys have no special meaning to a
name server or resolver. name server or resolver.
The following table summarizes some of the differences between DNSSEC The following table summarizes some of the differences between DNSSEC
keys and application keys: keys and application keys:
1. They serve different purposes. 1. They serve different purposes.
2. They are managed by different administrators. 2. They are managed by different administrators.
3. They are authenticated according to different rules. 3. They are authenticated according to different rules.
4. Nameservers use different rules when including them in responses. 4. Nameservers use different rules when including them in
responses.
5. Resolvers process them in different ways. 5. Resolvers process them in different ways.
6. Faults/key compromises have different consequences. 6. Faults/key compromises have different consequences.
1. The purpose of a DNSSEC key is to sign resource records 1. The purpose of a DNSSEC key is to sign resource records
associated with a DNS zone (or generate DNS transaction signatures associated with a DNS zone (or generate DNS transaction signatures in
in the case of SIG(0)/TKEY). But the purpose of an application key the case of SIG(0)/TKEY). But the purpose of an application key is
is specific to the application. Application keys, such as PGP/email, specific to the application. Application keys, such as PGP/email,
IPSEC, TLS, and SSH keys, are not a mandatory part of any zone and 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 the purpose and proper use of application keys is outside the scope
of DNS. of DNS.
2. DNSSEC keys are managed by DNS administrators, but application 2. DNSSEC keys are managed by DNS administrators, but application
keys are managed by application administrators. The DNS zone keys are managed by application administrators. The DNS zone
administrator determines the key lifetime, handles any suspected key administrator determines the key lifetime, handles any suspected key
compromises, and manages any DNSSEC key changes. Likewise, the compromises, and manages any DNSSEC key changes. Likewise, the
application administrator is responsible for the same functions for application administrator is responsible for the same functions for
the application keys related to the application. For example, a user the application keys related to the application. For example, a user
typically manages her own PGP key and a server manages its own TLS typically manages her own PGP key and a server manages its own TLS
key. Application key management tasks are outside the scope of DNS key. Application key management tasks are outside the scope of DNS
administration. administration.
3. DNSSEC zone keys are used to authenticate application keys, but 3. DNSSEC zone keys are used to authenticate application keys, but
by definition application keys are not allowed to authenticate DNS by definition, application keys are not allowed to authenticate DNS
zone keys. A DNS zone key is either configured as trusted key or 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. authenticated by constructing a chain of trust in the DNS hierarchy.
To participate in the chain of trust, a DNS zone needs to exchange To participate in the chain of trust, a DNS zone needs to exchange
zone key information with its parent zone [3]. Application keys are 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 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 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 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 resolution to work. A resolver considers an application key RRset as
authenticated DNS information if it has a valid signature from the authenticated DNS information if it has a valid signature from the
local DNS zone keys, but applications could impose additional local DNS zone keys, but applications could impose additional
security requirements before the application key is accepted as security requirements before the application key is accepted as
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5. DNS zone keys require special handling by resolvers, but 5. DNS zone keys require special handling by resolvers, but
application keys are treated the same as any other type of DNS data. 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 The DNSSEC keys are of no value to end applications, unless the
applications plan to do their own DNS authentication. By definition, applications plan to do their own DNS authentication. By definition,
secure resolvers are not allowed to use application keys as part of secure resolvers are not allowed to use application keys as part of
the authentication process. Application keys have no unique meaning the authentication process. Application keys have no unique meaning
to resolvers and are only useful to the application requesting the to resolvers and are only useful to the application requesting the
key. Note that if sub-types are used to identify the application key. Note that if sub-types are used to identify the application
key, then either the interface to the resolver needs to specify the 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 sub-type or the application needs to be able to accept all KEY RRs
and pick out the desired the sub-type. and pick out the desired sub-type.
6. A fault or compromise of a DNS zone key can lead to invalid or 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 forged DNS data, but a fault or compromise of an application key
should have no impact on other DNS data. Incorrectly adding or should have no impact on other DNS data. Incorrectly adding or
changing a DNS zone key can invalidate all of the DNS data in zone changing a DNS zone key can invalidate all of the DNS data in the
and in all of its subzones. By using a compromised key, an attacker zone and in all of its subzones. By using a compromised key, an
can forge data from the effected zone and any for any of its sub- attacker can forge data from the effected zone and for any of its
zones. A fault or compromise of an application key has implications sub-zones. A fault or compromise of an application key has
for that application, but it should not have an impact on the DNS. implications for that application, but it should not have an impact
Note that application key faults and key compromises can have an on the DNS. Note that application key faults and key compromises can
impact on the entire DNS if the application key and DNS zone keys are have an impact on the entire DNS if the application key and DNS zone
both stored in the KEY RR. keys are both stored in the KEY RR.
In summary, DNSSEC keys and application keys differ in most every In summary, DNSSEC keys and application keys differ in most every
respect. DNSSEC keys are an essential part of the DNS infrastructure respect. DNSSEC keys are an essential part of the DNS infrastructure
and require special handling by DNS administrators and DNS resolvers. and require special handling by DNS administrators and DNS resolvers.
Application keys are simply another type of data and have no special Application keys are simply another type of data and have no special
meaning to DNS administrators or resolvers. These two different meaning to DNS administrators or resolvers. These two different
types of data do not belong in the same resource record. types of data do not belong in the same resource record.
3. Definition of the KEY Resource Record 3. Definition of the KEY RR
The KEY RR uses type 25 and is used as resource record for storing 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 DNSSEC keys. The RDATA for a KEY RR consists of flags, a protocol
octet, the algorithm number octet, and the public key itself. The octet, the algorithm number octet, and the public key itself. The
format is as follows: 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 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 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
skipping to change at page 8, line 47 skipping to change at page 6, line 47
Value 3 (DNSSEC) is unchanged. Value 3 (DNSSEC) is unchanged.
Value 4 (TLS) is renamed to RESERVED. Value 4 (TLS) is renamed to RESERVED.
Value 5-254 remains unchanged (reserved). Value 5-254 remains unchanged (reserved).
Value 255 (ANY) is renamed to RESERVED. Value 255 (ANY) is renamed to RESERVED.
The authoritative data for a zone MUST NOT include any KEY records The authoritative data for a zone MUST NOT include any KEY records
with a protocol octet other than 3. The registry maintained by IANA with a protocol octet other than 3. The registry maintained by IANA
for protocol values is closed for new assignemnts. for protocol values is closed for new assignments.
Name servers and resolvers SHOULD accept KEY RR sets that contain KEY 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 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 deprecated KEY RRs with a protocol octet value other than 3, then
simply dropping the deprecated KEY RRs from the KEY RR set would simply dropping the deprecated KEY RRs from the KEY RR set would
invalidate any associated SIG record(s) and could create caching invalidate any associated SIG record(s) and could create caching
consistency problems. Note that KEY RRs with a protocol octet value consistency problems. Note that KEY RRs with a protocol octet value
other than 3 MUST NOT be used to authenticate DNS data. other than 3 MUST NOT be used to authenticate DNS data.
The algorithm and public key fields are not changed. The algorithm and public key fields are not changed.
skipping to change at page 12, line 7 skipping to change at page 7, line 40
6. Storing Application Keys in the DNS 6. Storing Application Keys in the DNS
The scope of this document is strictly limited to the KEY record. The scope of this document is strictly limited to the KEY record.
This document prohibits storing application keys in 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 but it does not endorse or restrict the storing application keys in
other record types. Other documents can describe how DNS handles other record types. Other documents can describe how DNS handles
application keys. application keys.
7. IANA Considerations 7. IANA Considerations
RFC 2535 created an IANA registry for DNS KEY Resource Record RFC 2535 created an IANA registry for DNS KEY RR Protocol Octet
Protocol Octet values. Values to 1,2,3, 4, and 255 were assigned by values. Values 1, 2, 3, 4, and 255 were assigned by RFC 2535 and
RFC 2535 and values 5-254 were made available for assignment by IANA. values 5-254 were made available for assignment by IANA. This
This document makes two sets of changes to this registry. document makes two sets of changes to this registry.
First, this document re-assigns DNS KEY Resource Record Protocol First, this document re-assigns DNS KEY RR Protocol Octet values 1,
Octet values 1, 2, 4, and 255 to ``reserved''. DNS Key Resource 2, 4, and 255 to "reserved". DNS Key RR Protocol Octet Value 3
Record Protocol Octet Value 3 remains unchanged as ``DNSSEC''. remains unchanged as "DNSSEC".
Second, new values are no longer available for assignment by IANA and Second, new values are no longer available for assignment by IANA and
this document closes the IANA registry for DNS KEY Resource Record this document closes the IANA registry for DNS KEY RR Protocol Octet
Protocol Octet Values. Assignment of any future KEY Resource Record Values. Assignment of any future KEY RR Protocol Octet values
Protocol Octet values requires a standards action. requires a standards action.
8. Security Considerations 8. Security Considerations
This document eliminates potential security problems that could arise This document eliminates potential security problems that could arise
due to the coupling of DNS zone keys and application keys. Prior to due to the coupling of DNS zone keys and application keys. Prior to
the change described in this document, a correctly authenticated KEY the change described in this document, a correctly authenticated KEY
set could include both application keys and DNSSEC keys. This draft set could include both application keys and DNSSEC keys. This
restricts the KEY RR to DNS security usage only. This is an attempt document restricts the KEY RR to DNS security usage only. This is an
to simplify the security model and make it less user-error prone. If attempt to simplify the security model and make it less user-error
one of the application keys is compromised, it could be used as a prone. If one of the application keys is compromised, it could be
false zone key to create false DNS signatures (SIG records). used as a false zone key to create false DNS signatures (SIG
Resolvers that do not carefully check the KEY sub-type could believe records). Resolvers that do not carefully check the KEY sub-type
these false signatures and incorrectly authenticate DNS data. With could believe these false signatures and incorrectly authenticate DNS
this change, application keys cannot appear in an authenticated KEY data. With this change, application keys cannot appear in an
set and this vulnerability is eliminated. authenticated KEY set and this vulnerability is eliminated.
The format and correct usage of DNSSEC keys is not changed by this The format and correct usage of DNSSEC keys is not changed by this
document and no new security considerations are introduced. document and no new security considerations are introduced.
References (Normative) 9. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Eastlake, D., "Domain Name System Security Extensions", RFC [2] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999. 2535, March 1999.
[3] Eastlake, D., "Secret Key Establishment for DNS (TKEY RR)", RFC [3] Eastlake, D., "Secret Key Establishment for DNS (TKEY RR)", RFC
2930, September 2000. 2930, September 2000.
[4] Eastlake, D., "DNS Request and Transaction Signatures ( [4] Eastlake, D., "DNS Request and Transaction Signatures
SIG(0)s)", RFC 2931, September 2000. (SIG(0)s)", RFC 2931, September 2000.
[5] Wellington, B., "Secure Domain Name System (DNS) Dynamic [5] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, November 2000. Update", RFC 3007, November 2000.
Authors' Addresses 10. Authors' Addresses
Dan Massey Dan Massey
USC Information Sciences Institute USC Information Sciences Institute
3811 N. Fairfax Drive 3811 N. Fairfax Drive
Arlington, VA 22203 Arlington, VA 22203
USA USA
EMail: masseyd@isi.edu EMail: masseyd@isi.edu
Scott Rose Scott Rose
National Institute for Standards and Technology National Institute for Standards and Technology
100 Bureau Drive 100 Bureau Drive
Gaithersburg, MD 20899-3460 Gaithersburg, MD 20899-3460
USA USA
EMail: scott.rose@nist.gov EMail: scott.rose@nist.gov
Full Copyright Statement 11. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved. Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
 End of changes. 

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