draft-ietf-dnsext-restrict-key-for-dnssec-00.txt   draft-ietf-dnsext-restrict-key-for-dnssec-01.txt 
D. Massey
DNSEXT Working Group D. Massey USC/ISI
INTERNET-DRAFT USC/ISI
S. Rose S. Rose
Expires: April 2002 NIST NIST
Updates: RFC 2535 November 2001
Limiting the Scope of the KEY Resource Record Limiting the Scope of the KEY Resource Record
------------------------------
<draft-ietf-dnsext-restrict-key-for-dnssec-00.txt> draft-ietf-dnsext-restrict-key-for-dnssec-01.txt
Status of this Document Status of this Document
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Abstract Abstract
This document limits the KEY resource record to only DNS zone keys. This document limits the KEY resource record to only DNSSEC
The original KEY resource record used sub-typing to store both DNS keys. The original KEY resource record used sub-typing
zone keys and arbitrary application keys. DNS security keys and to store both DNSSEC keys and arbitrary application keys.
application keys differ in almost every respect and should not be Storing both DNSSEC and application keys in one record was
combined in a single sub-typed resource record. This document a mistake. This document removes application keys from
removes application keys from the KEY record by redefining the the KEY record by redefining the Protocol Octet field in
Protocol Octet field in the KEY RDATA. Three existing application key the KEY RDATA. As a result of removing application keys,
sub-types are changed to historic, but the format of the KEY record all but one of the flags in the KEY record become unnecessary
and are removed. Three existing application key sub-types
are changed to historic, but the format of the KEY record
is not changed. This document updates RFC 2535. is not changed. This document updates RFC 2535.
1. Introduction 1 Introduction
This document limits the scope the KEY resource record. The KEY This document limits the scope the KEY resource record. The KEY
resource record, originally defined in [DNSSEC], uses resource record resource record was defined in [DNSSEC] and used resource record
sub-typing to hold any public key associated with "a zone, a user, or sub-typing to hold arbitrary public keys such as Email, IPSEC, DNSSEC,
a host or other end entity". The KEY resource record is assigned and TLS keys. This document eliminates the existing Email, IPSEC,
type value of 25 and the Protocol Octet in the KEY RDATA identifies and TLS sub-types and prohibits the introduction of new sub-types.
the sub-type. DNSSEC Zone, User and Host keys are stored in the KEY DNSSEC will be the only allowable sub-type for the KEY record (hence
resource record and are identified by a Protocol Octet value of 3. sub-typing is essentially eliminated) and all but one of the KEY
Email, IPSEC, and TLS keys are also stored in the KEY resource record record flags are also eliminated.
and are identified by Protocol Octet values of 1,2, and 4
(respectively). Protocol Octet values 5-254 are available for Section 2 presents the motivation for restricting the KEY record
assignment by IANA and values have been requested (but not assigned) and Section ?? defines the revised KEY record. Section 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 record and simplifies the flabs, does not change DNSSEC keys.
2 Motivation for Restricting the KEY Record
The KEY record RDATA [DNSSEC] consists of flags, a Protocol Octet,
an Algorithm type, and a public key. The Protocol Octet identifies
the KEY record sub-type. DNSSEC public keys are stored in the KEY
using a Protocol Octet value of 3. Email, IPSEC, and TLS keys are
also stored in the KEY resource record and using Protocol Octet values
of 1,2, and 4 (respectively). Protocol Octet values 5-254 are available
for assignment by IANA and values have been requested (but not assigned)
for applications such as SSH. for applications such as SSH.
Closer examination and limited experimental deployment has shown that Any use of sub-typing has inherent limitations. A resolver can not
application keys stored in KEY records are problematic. Any use of specify the desired sub-type in a DNS query and most DNS operations
sub-typing has inherent limitations. A resolver can not specify the apply only to resource records sets. For a example, a resolver can
desired sub-type in a DNS query and many DNS operations group not directly request KEY records with a particular sub-type. Instead,
resource records into sets, based on the DNS name and type. For a the resolver must request all KEY records associated with a DNS name
example, a resolver can not directly request the DNSSEC key sub-type. and then search the set for the desired sub-type. DNSSEC signatures
Instead, the resolver must request all KEY records associated with a also apply to the set of all KEY resource records associated with
DNS name. DNSSEC signatures apply to the set of all KEY resource the DNS name, regardless of sub-type.
records associated with the DNS name, regardless of sub-type.
In the case of the KEY record, 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 records are problematic.
In the case of the KEY record, the inherent sub-type limitations are
exacerbated since DNS zone keys and application keys differ in
virtually every respect. Combining two very different types of keys
into a single sub-typed resource record adds unnecessary complexity
and increases the potential for implementation and deployment errors.
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 resource record. Note that the scope of this document
is strictly limited to the KEY record and this document does not is strictly limited to the KEY record and this document does not
endorse or restrict the storage of application keys in other resource endorse or restrict the storage of application keys in other resource
records. records.
2. DNS Zone Key and Application Key Differences 2.1 Differences Between DNSSEC and Application Keys
In the original specification, all public keys were stored in KEY DNSSEC keys are an essential part of the DNSSEC protocol and are
records, regardless of protocol or type. This proved to be a mistake used by both name servers and resolvers in order to perform DNS tasks.
as DNS security keys (zone, host and user) and application keys A DNS zone, used to sign and authenticate RR sets, is most common
differ in the following ways: example of a DNSSEC key. SIG(0) and TKEY also use DNSSEC keys.
Application keys such as Email keys, IPSEC keys, and TLS keys and
are simply another type data. These keys have no special meaning
to a name server or resolver.
o They serve different purposes. o They serve different purposes.
o They are managed by different administrators. o They are managed by different administrators.
o They are authenticated according to different rules. o They are authenticated according to different rules.
o Nameservers use different rules when including them in o Nameservers use different rules when including them in responses.
responses.
o Resolvers process them in different ways. o Resolvers process them in different ways.
o Faults/key compromises have different consequences. o Faults/key compromises have different consequences.
The purpose of a DNS zone key is to sign resource records associated The purpose of a DNSSEC key is to sign resource records associated
with a DNS zone but the purpose of an application key is specific to with a DNS zone (or generate DNS transaction signatures in the case
the application. DNSSEC host and user KEY RRs are used to generate of SIG(0)/TKEY). But the purpose of an application key is specific
SIG(0) transaction signatures. Application keys, such as PGP/email, to the application. Application keys, such as PGP/email, IPSEC, TLS,
IPSEC, TLS, and SSH keys, are not a mandatory part of any zone and and SSH keys, are not a mandatory part of any zone and the purpose
the purpose and proper use of application keys is outside the scope and proper use of application keys is outside the scope of DNS.
of DNS.
DNSSEC keys are managed by DNS administrators, but application keys DNSSEC keys are managed by DNS administrators, but application keys
are managed by application administrators. The DNS zone administra- are managed by application administrators. The DNS zone administrator
tor determines the key lifetime, handles any suspected key comprom- determines the key lifetime, handles any suspected key compromises,
ises, and manages any DNSSEC key changes. Likewise, the application and manages any DNSSEC key changes. Likewise, the application administrator
administrator is responsible for the same functions for the applica- is responsible for the same functions for the application keys related
tion keys related to the application. For example, a user typically to the application. For example, a user typically manages her own
manages her own PGP key and a server manages its own TLS key. PGP key and a server manages its own TLS key. Application key management
Application key management tasks are outside the scope of DNS tasks are outside the scope of DNS administration.
administration.
DNS zone keys are used to authenticate application keys, but applica- DNSSEC zone keys are used to authenticate application keys, but application
tion keys MUST NOT be used to authenticate DNS zone keys. A DNS keys MUST NOT be used to authenticate DNS zone keys. A DNS zone
zone key is either configured as trusted key or authenticated by con- key is either configured as trusted key or authenticated by constructing
structing a chain of trust in the DNS hierarchy. To participate in a chain of trust in the DNS hierarchy. To participate in the chain
the chain of trust, a DNS zone must exchange zone key information of trust, a DNS zone must exchange zone key information with its
with its parent zone [DNSSEC]. Application keys are not configured parent zone [DNSSEC]. Application keys are not configured as trusted
as trusted keys in the DNS and are never part of any DNS chain of keys in the DNS and are never part of any DNS chain of trust. Application
trust. Application key data should not be exchanged with the parent key data should not be exchanged with the parent zone. A resolver
zone. A resolver considers an application key authenticated if it considers an application key authenticated if it has a valid signature
has a valid signature from the local DNS zone keys, but applications from the local DNS zone keys, but applications may impose additional
may impose additional requirements before the application key is requirements before the application key is accepted as authentic.
accepted as authentic.
It MAY be useful for nameservers to include DNS zone keys in the It MAY be useful for nameservers to include DNS zone keys in the
additional section of a response, but application keys are typically additional section of a response, but application keys are typically
not useful unless they have been specifically requested. For exam- not useful unless they have been specifically requested. For example,
ple, it may be useful to include the isi.edu zone key along with a it may be useful to include the isi.edu zone key along with a response
response that contain the www.isi.edu A record and SIG record. A that contain the www.isi.edu A record and SIG record. A secure resolver
secure resolver will need the isi.edu zone key in order to check the will need the isi.edu zone key in order to check the SIG and authenticate
SIG and authenticate the www.isi.edu A record. It is typical not the www.isi.edu A record. It is typical not useful to include the
useful to include the IPSEC, email, and TLS keys along with the A IPSEC, email, and TLS keys along with the A record. Note that by
record. Note that by placing application keys in the KEY record, a placing application keys in the KEY record, a resolver will need
resolver will need the IPSEC, email, TLS, and other key associated the IPSEC, email, TLS, and other key associated with isi.edu if the
with isi.edu if the resolver intends to authenticate the isi.edu zone resolver intends to authenticate the isi.edu zone key (since signatures
key (since signatures only apply to the entire KEY set). only apply to the entire KEY set).
DNS zone keys require special handling by resolvers, but application DNS zone keys require special handling by resolvers, but application
keys should be treated the same as any other type of DNS data. The keys should be treated the same as any other type of DNS data. The
DNSSEC keys are of no value to end applications, unless the applica- DNSSEC keys are of no value to end applications, unless the applications
tions plan to do their own DNS authentication. Secure resolvers plan to do their own DNS authentication. Secure resolvers MUST NOT
MUST NOT use application keys as part of the authentication process. use application keys as part of the authentication process. Application
Application keys have no unique value to resolvers and are only use- keys have no unique value to resolvers and are only useful to the
ful to the application requesting the key. Note that if sub-types application requesting the key. Note that if sub-types are used
are used to identify the application key, then either the interface to identify the application key, then either the interface to the
to the resolver must specify the sub-type or the application must be resolver must specify the sub-type or the application must be able
able to accept all KEY records and pick out the desired the sub-type. to accept all KEY records and pick out the desired the sub-type.
A fault or compromise of DNS zone key can lead to invalid or forged A fault or compromise of DNS zone key can lead to invalid or forged
DNS data, but a fault or compromise of an application key should have DNS data, but a fault or compromise of an application key should
no impact on other DNS data. Incorrectly adding or changing a DNS have no impact on other DNS data. Incorrectly adding or changing
zone key can invalidate all of the DNS data in zone and in all of its a DNS zone key can invalidate all of the DNS data in zone and in
subzones. By using a compromised key, an attacker can forge data all of its subzones. By using a compromised key, an attacker can
from the effected zone and any for any of its sub-zones. A fault or forge data from the effected zone and any for any of its sub-zones.
compromise of an application key has implications for that applica- A fault or compromise of an application key has implications for
tion, but it should not have an impact on the DNS. Note that applica- that application, but it should not have an impact on the DNS. Note
tion key faults and key compromises can have an impact on the entire that application key faults and key compromises can have an impact
DNS if the application key and DNS zone keys are both stored in the on the entire DNS if the application key and DNS zone keys are both
KEY record. stored in the KEY record.
In summary, DNS zone keys and application keys differ in most every In summary, DNSSEC keys and application keys differ in most every
respect. DNS zone keys are an essential part of the DNS infrastruc- respect. DNSSEC keys are an essential part of the DNS infrastructure
ture and require special handling by DNS administrators and DNS and require special handling by DNS administrators and DNS resolvers.
resolvers. Application keys are simply another type of data and have Application keys are simply another type of data and have no special
no special meaning to DNS administrators or resolvers. These two meaning to DNS administrators or resolvers. These two different types
different types of data do not belong in the same resource record. of data do not belong in the same resource record.
3. Redefinition of the KEY Resource Record 3 Definition of the KEY Resource Record
The KEY record is redefined as resource record for storing DNSSEC The KEY record uses type 25 and is used as resource record for storing
keys. The KEY RDATA format, as defined in [DNSSEC], is not changed, DNSSEC keys. The RDATA for a KEY RR consists of flags, a protocol
but the Protocol Octet is redefined as follows: octet, the algorithm number octet, and the public key itself. The
format is as follows:
VALUE Protocol 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 - reserved 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
1 HISTORIC +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 HISTORIC | flags | protocol | algorithm |
3 dnssec +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 HISTORIC | |
5-254 - reserved / public key /
255 HISTORIC / /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
All valid KEY records MUST have a Protocol Octet value of 3. KEY In the flags field, all bits except bit 7 are reserved should be
records with a Protocol Octet value other than 3 SHOULD NOT be stored zero. If Bit 7 (Zone bit) is set to 1, then the KEY is a DNS Zone
in the DNS and SHOULD be ignored by nameservers and resolvers that key. If Bit 7 is set to 0, the KEY is not a zone key. SIG(0)/TKEY
receive them in a response. are examples of DNSSEC keys that are not zone keys.
4. Backward Compatibility The protocol field must be set to 3.
Protocol Octet values of 1,2, 4, and 255 were previously defined in The algorithm and public key fields are not changed.
RFC 2535. These values are now deprecated. To insure backward
compatibility, the Protocol Octet values 1,2, and 4 will be desig-
nated as HISTORIC. Protocol values 5-254 are reserved and are no
longer available for assignment by IANA.
KEY records with a Protocol Value of 1,2, or 4 were never widely 4 Changes from RFC 2535 KEY Record
deployed in the DNS and some limited test deployment revealed prob-
lems. Most notably, placing application keys in the KEY record can
create very large key sets and application keys that appear in the
zone apex can create zone management problems. Some change in the
definition and/or usage of the KEY record would be required even if
the approach described here were not required.
KEY records with a Protocol Octet value of 1,2, or 4 SHOULD NOT be The KEY RDATA format is not changed.
place in a DNS zone. Likewise, resolvers that receive KEY records
in a response with HISTORIC or invalid protocol field values SHOULD
be ignored and SHOULD NOT be stored in a resolver's/server's cache.
No changes are made to the format of the KEY record or to the use of All flags except for the zone key flag are eliminated:
DNSSEC zone, host and user keys. Existing nameservers and resolvers
will continue to correctly process KEY records that contain DNSSEC
keys.
5. Storing Application Keys in the DNS o The A/C bits (bits 0 and 1) are eliminated and must be 0.
o The extended flags bit (bit 3) is eliminated and must be 0.
o The host/user bit (bit 6) is eliminated and must be 0.
o The zone bit (bit 7) remains unchanged.
o The signatory field (bits 12-15) are eliminated by [SDU] and
must be 0.
o Bits 2,4,5,8,9,10,11 remain unchanged. They are reserved and
must be zero.
All Protocol Octet values except DNSSEC (3) are eliminated:
o Value 1 (Email) is renamed to reserved.
o Value 2 (IPSEC) is renamed to reserved.
o Value 3 (DNSSEC) is unchanged.
o Value 4 (TLS) is renamed to reserved.
o Value 5-254 remains unchanged (reserved).
o Value 255 (ANY) is renamed to reserved.
Name servers and resolvers SHOULD reject any KEY with a Protocol
other than 3.
The algorithm and public key fields are not changed.
5 Backward Compatibility
No backwards compatibility is provided for application keys. Any
Email, IPSEC, or TLS keys are now deprecated and SHOULD be rejected
by name servers and resolvers. However, problems with applications
keys (such as keys at the apex and large RR sets) and have already
been identified some change in the definition and/or usage of the
KEY record would be required even if the approach described here
were not required.
DNSSEC zone KEY records are not change 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 records (SIG(0)/TKEY keys) are backwards compatible,
but the distinction between host and user keys (flag bit 6) is lost.
Overall, existing nameservers and resolvers will continue to correctly
process KEY records 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. 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
other record types. Other documents should describe how DNS handles in other record types. Other documents should describe how DNS handles
application keys. application keys.
6. IANA Consideration 7 IANA Consideration
Protocol Octet values 1,2,4, and 255 are changed to HISTORIC. KEY record Protocol Octet values 1,2,4, and 255 should be changed
to reserved.
Protocol Octet values 5-255 are reserved and are no longer available Assignment of any future KEY record Protocol Octet values requires
for assignment by IANA. a standards action.
7. Security Consideration 8 Security Consideration
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. due to the coupling of DNS zone keys and application keys. Prior
to the change described in the document, a correctly authenticated
Prior to the change described in the document, a correctly authenti- KEY set could include both application keys and DNSSEC keys. If
cated KEY set could include both application keys and DNSSEC keys. one of the application keys is compromised, it could be used as a
If one of the application keys is compromised, it could be used as a false zone key to create phony DNS signatures (SIG records). Resolvers
false zone key to create phony DNS signatures (SIG records). that do not carefully check the KEY sub-type may believe these false
Resolvers that do not carefully check the KEY sub-type may believe signatures and incorrectly authenticate DNS data. With this change,
these false signatures and incorrectly authenticate DNS data. With application keys cannot appear in an authenticated KEY set and this
this change, application keys cannot appear in an authenticated KEY vulnerability is eliminated.
set.
Applications that accept keys based solely on DNSSEC rely on the DNS
administrator to correctly enter the application key data and are
only as secure as the weakest zone in the DNS chain of trust.
Compromises or errors caused by DNS administrators when entering
DNSSEC data could results in an application key failing to verify, or
verified incorrectly.
The format and correct usage of DNS zone 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.
8. Intellectual Property 9 Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to per- intellectual property or other rights that might be claimed to pertain
tain to the implementation or use of the technology described in this to the implementation or use of the technology described in this
document or the extent to which any license under such rights might document or the extent to which any license under such rights might
or might not be available; neither does it represent that it has made or might not be available; neither does it represent that it has
any effort to identify any such rights. Information on the IETF's made any effort to identify any such rights. Information on the
procedures with respect to rights in standards-track and standards- IETF's procedures with respect to rights in standards-track and standards-
related documentation can be found in BCP-11. related documentation can be found in BCP-11.
Copies of claims of rights made available for publication and any Copies of claims of rights made available for publication and any
assurances of licenses to be made available, or the result of an 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 attempt made to obtain a general license or permission for the use
such proprietary rights by implementors or users of this specifica- of such proprietary rights by implementors or users of this specification
tion can be obtained from the IETF Secretariat. can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary rights
rights which may cover technology that may be required to practice which may cover technology that may be required to practice this
this standard. Please address the information to the IETF Executive standard. Please address the information to the IETF Executive Director.
Director.
9. References 10 References
[DNSSEC] Eastlake, D., "Domain Name System Security Extensions", RFC [DNSSEC] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999. 2535, March 1999.
10. Author Information [SDU] Wellington, B., "Secure Domain Name System (DNS) Dynamic Update",
RFC 3007, November 2000.
11 Author Information
Daniel Massey <masseyd@isi.edu> Daniel Massey <masseyd@isi.edu>
USC Information Sciences Institute USC Information Sciences Institute
3811 North Fairfax Drive, Suite 200 3811 North Fairfax Drive, Suite 200
Arlington, VA 22203 Arlington, VA 22203
Scott Rose <scott.rose@nist.gov> Scott Rose <scott.rose@nist.gov>
National Institute for Standards and Technology National Institute for Standards and Technology
Gaithersburg, MD Gaithersburg, MD
Expiration and File Name:
This draft, titled <draft-ietf-dnsext-restrict-key-for-dnssec-00.txt> expires April 2001
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved. Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished This document and translations of it may be copied and furnished
to others, and derivative works that comment on or otherwise explain to others, and derivative works that comment on or otherwise explain
it or assist in its implementation may be prepared, copied, published it 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 copy- right notice and this paragraph kind, provided that the above copy- right notice and this paragraph
are included on all such copies and derivative works. However, this are included on all such copies and derivative works. However, this
 End of changes. 

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