draft-ietf-dnsext-dnssec-algo-signal-07.txt   draft-ietf-dnsext-dnssec-algo-signal-08.txt 
DNS Extensions Working Group S. Crocker DNS Extensions Working Group S. Crocker
Internet-Draft Shinkuro Inc. Internet-Draft Shinkuro Inc.
Intended status: Standards Track S. Rose Intended status: Standards Track S. Rose
Expires: December 16, 2012 NIST Expires: February 15, 2013 NIST
June 14, 2012 August 14, 2012
Signaling Cryptographic Algorithm Understanding in DNSSEC Signaling Cryptographic Algorithm Understanding in DNSSEC
draft-ietf-dnsext-dnssec-algo-signal-07 draft-ietf-dnsext-dnssec-algo-signal-08
Abstract Abstract
The DNS Security Extensions (DNSSEC) were developed to provide origin The DNS Security Extensions (DNSSEC) were developed to provide origin
authentication and integrity protection for DNS data by using digital authentication and integrity protection for DNS data by using digital
signatures. These digital signatures can be generated using signatures. These digital signatures can be generated using
different algorithms. This draft sets out to specify a way for different algorithms. This draft sets out to specify a way for
validating end-system resolvers to signal to a server which digital validating end-system resolvers to signal to a server which digital
signature and hash algorithms they support. signature and hash algorithms they support.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 16, 2012. This Internet-Draft will expire on February 15, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Likewise, Delegation Signer (DS) RRs and NSEC3 RRs use a hashed value Likewise, Delegation Signer (DS) RRs and NSEC3 RRs use a hashed value
as part of their RDATA and, like digital signature algorithms, these as part of their RDATA and, like digital signature algorithms, these
hash algorithms have code numbers. All three algorithm codes (RRSIG/ hash algorithms have code numbers. All three algorithm codes (RRSIG/
DNSKEY, DS and NSEC3) are maintained in unique IANA registries. DNSKEY, DS and NSEC3) are maintained in unique IANA registries.
This draft sets out to specify a way for validating end-system This draft sets out to specify a way for validating end-system
resolvers to tell a server in a DNS query which digital signature resolvers to tell a server in a DNS query which digital signature
and/or hash algorithms they support. This is done using the new EDNS and/or hash algorithms they support. This is done using the new EDNS
options specified below in Section 2 for use in the OPT meta-RR options specified below in Section 2 for use in the OPT meta-RR
[I-D.ietf-dnsext-rfc2671bis-edns0]. [I-D.ietf-dnsext-rfc2671bis-edns0]. These three new EDNS option
codes are all OPTIONAL to implement and use.
These proposed EDNS options serve to measure the acceptance and use These proposed EDNS options serve to measure the acceptance and use
of new digital signing algorithms. These signaling options can be of new digital signing algorithms. These signaling options can be
used by zone administrators as a gauge to measure the successful used by zone administrators as a gauge to measure the successful
deployment of code that implements newly deployed digital signature deployment of code that implements newly deployed digital signature
algorithm, DS hash and NSEC3 hash algorithm used with DNSSEC. A zone algorithm, DS hash and NSEC3 hash algorithm used with DNSSEC. A zone
administrator is able to determine when to stop signing with a administrator is able to determine when to stop signing with a
superseded algorithm when the server sees that a significant number superseded algorithm when the server sees that a significant number
of its clients signal that they are able to accept the new algorithm. of its clients signal that they are able to accept the new algorithm.
Note that this survey may be conducted over the period of years Note that this survey may be conducted over the period of years
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2. Signaling DNSSEC Algorithm Understood (DAU), DS Hash Understood 2. Signaling DNSSEC Algorithm Understood (DAU), DS Hash Understood
(DHU) and NSEC3 Hash Understood (N3U) Using EDNS (DHU) and NSEC3 Hash Understood (N3U) Using EDNS
The EDNS0 specification outlined in The EDNS0 specification outlined in
[I-D.ietf-dnsext-rfc2671bis-edns0] defines a way to include new [I-D.ietf-dnsext-rfc2671bis-edns0] defines a way to include new
options using a standardized mechanism. These options are contained options using a standardized mechanism. These options are contained
in the RDATA of the OPT meta-RR. This document defines three new in the RDATA of the OPT meta-RR. This document defines three new
EDNS options for a client to signal which digital signature and/or EDNS options for a client to signal which digital signature and/or
hash algorithms the client supports. These options can be used hash algorithms the client supports. These options can be used
independently of each other and MAY appear in any order in the OPT independently of each other and MAY appear in any order in the OPT
RR. RR. Each option code can appear only once in an OPT RR.
The figure below shows how each option is defined in the RDATA of the The figure below shows how each option is defined in the RDATA of the
OPT RR specified in [I-D.ietf-dnsext-rfc2671bis-edns0]: OPT RR specified in [I-D.ietf-dnsext-rfc2671bis-edns0]:
0 8 16 0 8 16
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| OPTION-CODE (TBD) | | OPTION-CODE (TBD) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| LIST-LENGTH | | LIST-LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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o NSEC3 Hash Understood (N3U) option for NSEC3 hash algorithms. Its o NSEC3 Hash Understood (N3U) option for NSEC3 hash algorithms. Its
value is fixed at TBD3. value is fixed at TBD3.
LIST-LENGTH is the length of the list of digital signature or hash LIST-LENGTH is the length of the list of digital signature or hash
algorithm codes in octets. Each algorithm code occupies a single algorithm codes in octets. Each algorithm code occupies a single
octet. octet.
ALG-CODE is the list of assigned values of DNSSEC zone signing ALG-CODE is the list of assigned values of DNSSEC zone signing
algorithms, DS hash algorithms, or NSEC3 hash algorithms (depending algorithms, DS hash algorithms, or NSEC3 hash algorithms (depending
on the OPTION-CODE in use) that the client declares to be supported. on the OPTION-CODE in use) that the client declares to be supported.
The values are listed in descending order of preference, with the The order of the code values can be arbitrary and SHOULD NOT be used
most preferred algorithm first. For example, if a validating client to infer preference.
signals the DAU option and RSA/SHA-1, RSA/SHA-256 and prefers the
latter, the values of ALG-CODE would be: 8 (RSA/SHA-256), 5 (RSA/
SHA-1).
If all three options are included in the OPT RR, there is a potential If all three options are included in the OPT RR, there is a potential
for the OPT RR to take up considerable size in the DNS message. for the OPT RR to take up considerable size in the DNS message.
However, in practical terms, including all three options is likely to However, in practical terms, including all three options is likely to
take up 22-32 octets (average of 6-10 digital signature algorithms, take up 22-32 octets (average of 6-10 digital signature algorithms,
3-5 DS hash algorithms and 1-5 NSEC3 hash algorithms) including the 3-5 DS hash algorithms and 1-5 NSEC3 hash algorithms) including the
EDNS option codes and option lengths in a potential future example. EDNS option codes and option lengths in a potential future example.
3. Client Considerations 3. Client Considerations
A validating end-system resolver sets the DAU, DHU and/or N3U option, A validating end-system resolver sets the DAU, DHU and/or N3U option,
or combination thereof in the OPT meta-RR when sending a query. The or combination thereof in the OPT meta-RR when sending a query. The
validating end-system resolver sets the value(s) in the order of validating end-system resolver sets the value(s) in any arbitrary
preference, with the most preferred algorithm(s) first as described order. The validating end-system resolver MUST also set the
in section 2. The validating end-system resolver MUST also set the
DNSSEC-OK bit [RFC4035] to indicate that it wishes to receive DNSSEC DNSSEC-OK bit [RFC4035] to indicate that it wishes to receive DNSSEC
RRs in the response. RRs in the response.
Note that the PRIVATEDNS (253) and/or the PRIVATEOID (254) digital Note that the PRIVATEDNS (253) and/or the PRIVATEOID (254) digital
signature codes both cover a potentially wide range of algorithms and signature codes both cover a potentially wide range of algorithms and
are likely not useful to a server. There is no compelling reason for are likely not useful to a server. There is no compelling reason for
a client to include these codes in its list of the DAU. Likewise, a client to include these codes in its list of the DAU. Likewise,
clients MUST NOT include RESERVED codes in any of the options. clients MUST NOT include RESERVED codes in any of the options.
3.1. Stub Resolvers 3.1. Stub Resolvers
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cache) to provide a response. So optimal setting of the DAU, DSU and cache) to provide a response. So optimal setting of the DAU, DSU and
N3U options depends on whether the stub resolver elects to perform N3U options depends on whether the stub resolver elects to perform
its own validation. its own validation.
3.1.1. Validating Stub Resolvers 3.1.1. Validating Stub Resolvers
A validating stub resolver already (usually) sets the DO bit A validating stub resolver already (usually) sets the DO bit
[RFC4035] to indicate that it wishes to receive additional DNSSEC RRs [RFC4035] to indicate that it wishes to receive additional DNSSEC RRs
(i.e. RRSIG RRs) in the response. Such validating resolvers SHOULD (i.e. RRSIG RRs) in the response. Such validating resolvers SHOULD
include the DAU, DHU and/or the N3U option(s) in the OPT RR when include the DAU, DHU and/or the N3U option(s) in the OPT RR when
sending a query. The way the validating stub resolver indicates sending a query.
which cryptographic algorithm(s) it supports by setting the values in
the order of preference, with the most preferred algorithm first as
described in Section 2.
3.1.2. Non-Validating Stub Resolvers 3.1.2. Non-Validating Stub Resolvers
The DAU, DHU and N3U EDNS options are NOT RECOMMENDED for non- The DAU, DHU and N3U EDNS options are NOT RECOMMENDED for non-
validating stub resolvers. validating stub resolvers.
3.2. Recursive Resolvers 3.2. Recursive Resolvers
3.2.1. Validating Recursive Resolvers 3.2.1. Validating Recursive Resolvers
A validating recursive resolver sets the DAU, DHU and/or N3U A validating recursive resolver sets the DAU, DHU and/or N3U
option(s) when performing recursion based on the DO and CD flags in option(s) when performing recursion based on its list of algorithms
the client request [RFC4035]. If the client of the recursive and any DAU, DHU and/or N3U option lists in the stub client query.
resolver did not include the DO bit in the query the recursive When the recursive server receives a query with one or more of the
resolver MAY include the option(s) according to its own local policy. options set, the recursive server MUST set the algorithm list to a
union of the stub client's list and the validating recursive
resolver's list. For example, if the recursive resolver's algorithm
list for the DAU option is (3, 5, 7) and the stub's algorithm list is
(7, 8), the final DAU algorithm list would be (3, 5, 7, 8).
If the client did include the DO and CD bits, but did not include the If the client did include the DO and CD bits, but did not include the
DAU, DHU and/or N3U option(s) in the query, the validating recursive DAU, DHU and/or N3U option(s) in the query, the validating recursive
resolver MUST NOT include the option(s) to avoid conflicts. resolver MAY include the option(s) with its own list in full. If one
or more of the options are missing, the validating recursive resolver
If the client did set the DO bit and the option(s) in the query, the MAY include the missing options with its own list in full.
validating recursive resolver MUST include the option(s) based on the
setting of the CD bit. If the CD bit is set, the validating
recursive resolver MUST include the option(s) based on the client
query or a superset of the client option(s) list and the validator's
own list (if different). If the CD bit is not set, the validating
recursive resolver MAY copy the client option(s) or substitute its
own option list.
3.2.2. Non-validating Recursive Resolvers 3.2.2. Non-validating Recursive Resolvers
Recursive resolvers that do not do validation MUST copy the DAU, DHU Recursive resolvers that do not do validation MUST copy the DAU, DHU
and/or N3U option(s) seen in received queries as they represent the and/or N3U option(s) seen in received queries as they represent the
wishes of the validating downstream resolver that issued the original wishes of the validating downstream resolver that issued the original
query. query.
4. Intermediate System Considerations 4. Intermediate System Considerations
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processing (e.g. RRSIG filtering in responses) on the server side. processing (e.g. RRSIG filtering in responses) on the server side.
If the options are present but the DNSSEC-OK (OK) bit is not set, the If the options are present but the DNSSEC-OK (OK) bit is not set, the
server does not do any DNSSEC processing, including any recording of server does not do any DNSSEC processing, including any recording of
the option(s). the option(s).
6. Traffic Analysis Considerations 6. Traffic Analysis Considerations
Zone administrators that are planning or are in the process of a Zone administrators that are planning or are in the process of a
cryptographic algorithm rollover operation should monitor DNS query cryptographic algorithm rollover operation should monitor DNS query
traffic and record the number of queries, the presense of the OPT RR traffic and record the number of queries, the presence of the OPT RR
in queries and the values of the DAU/DHU/N3U option(s) (if present). in queries and the values of the DAU/DHU/N3U option(s) (if present).
This monitoring can be used to measure the deployment of client code This monitoring can be used to measure the deployment of client code
that implements (and signals) specific algorithms. Description of that implements (and signals) specific algorithms. Description of
the techniques used to capture DNS traffic and measure new algorithm the techniques used to capture DNS traffic and measure new algorithm
adoption is beyond the scope of this document. adoption is beyond the scope of this document.
Zone administrators that need to comply with changes to their Zone administrators that need to comply with changes to their
organization's security policy (with regards to cryptographic organization's security policy (with regards to cryptographic
algorithm use) can use this data to set milestone dates for algorithm use) can use this data to set milestone dates for
performing an algorithm rollover. For example, zone administrators performing an algorithm rollover. For example, zone administrators
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8. Security Considerations 8. Security Considerations
This document specifies a way for a client to signal its digital This document specifies a way for a client to signal its digital
signature and hash algorithm knowledge to a cache or server. It is signature and hash algorithm knowledge to a cache or server. It is
not meant to be a discussion on algorithm superiority. The signals not meant to be a discussion on algorithm superiority. The signals
are optional codes contained in the OPT meta-RR used with EDNS. The are optional codes contained in the OPT meta-RR used with EDNS. The
goal of these options are to signal new algorithm uptake in client goal of these options are to signal new algorithm uptake in client
code to allow zone administrators to know when it is possible to code to allow zone administrators to know when it is possible to
complete an algorithm rollover in a DNSSEC signed zone. complete an algorithm rollover in a DNSSEC signed zone.
There is a possibility that an eavesdropper or server could infer the
validator in use by a client by the presence of the AU options and/or
algorithm code list. This information leakage in itself is not very
useful to a potential attacker but it could be used to identify the
validator or narrow down the possible validator implementations in
use by a client, which could have a known vulnerability that could be
exploited by the attacker.
9. Normative References 9. Normative References
[I-D.ietf-dnsext-rfc2671bis-edns0] Damas, J., Graff, M., and P. [I-D.ietf-dnsext-rfc2671bis-edns0] Damas, J., Graff, M., and P.
Vixie, "Extension Mechanisms for Vixie, "Extension Mechanisms for
DNS (EDNS0)", draft-ietf-dnsext- DNS (EDNS0)", draft-ietf-dnsext-
rfc2671bis-edns0-08 (work in rfc2671bis-edns0-09 (work in
progress), February 2012. progress), August 2012.
[RFC2119] Bradner, S., "Key words for use [RFC2119] Bradner, S., "Key words for use
in RFCs to Indicate Requirement in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, Levels", BCP 14, RFC 2119,
March 1997. March 1997.
[RFC4033] Arends, R., Austein, R., Larson, [RFC4033] Arends, R., Austein, R., Larson,
M., Massey, D., and S. Rose, "DNS M., Massey, D., and S. Rose, "DNS
Security Introduction and Security Introduction and
Requirements", RFC 4033, Requirements", RFC 4033,
 End of changes. 13 change blocks. 
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