draft-ietf-dnsop-server-cookies-01.txt   draft-ietf-dnsop-server-cookies-02.txt 
DNSOP Working Group O. Sury DNSOP Working Group O. Sury
Internet-Draft Internet Systems Consortium Internet-Draft Internet Systems Consortium
Updates: 7873 (if approved) W. Toorop Updates: 7873 (if approved) W. Toorop
Intended status: Standards Track NLnet Labs Intended status: Standards Track NLnet Labs
Expires: May 7, 2020 D. Eastlake 3rd Expires: May 21, 2020 D. Eastlake 3rd
Futurewei Technologies Futurewei Technologies
M. Andrews M. Andrews
Internet Systems Consortium Internet Systems Consortium
November 4, 2019 November 18, 2019
Interoperable Domain Name System (DNS) Server Cookies Interoperable Domain Name System (DNS) Server Cookies
draft-ietf-dnsop-server-cookies-01 draft-ietf-dnsop-server-cookies-02
Abstract Abstract
DNS cookies, as specified in RFC 7873, are a lightweight DNS DNS cookies, as specified in RFC 7873, are a lightweight DNS
transaction security mechanism that provides limited protection to transaction security mechanism that provides limited protection to
DNS servers and clients against a variety of denial-of-service and DNS servers and clients against a variety of denial-of-service and
amplification, forgery, or cache poisoning attacks by off-path amplification, forgery, or cache poisoning attacks by off-path
attackers. attackers.
This document provides precise directions for creating Server Cookies This document provides precise directions for creating Server Cookies
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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 https://datatracker.ietf.org/drafts/current/. Drafts is at https://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 May 7, 2020. This Internet-Draft will expire on May 21, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 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
(https://trustee.ietf.org/license-info) in effect on the date of (https://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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2. Changes to [RFC7873] . . . . . . . . . . . . . . . . . . . . 4 2. Changes to [RFC7873] . . . . . . . . . . . . . . . . . . . . 4
3. Constructing a Client Cookie . . . . . . . . . . . . . . . . 4 3. Constructing a Client Cookie . . . . . . . . . . . . . . . . 4
4. Constructing a Server Cookie . . . . . . . . . . . . . . . . 5 4. Constructing a Server Cookie . . . . . . . . . . . . . . . . 5
4.1. The Version Sub-Field . . . . . . . . . . . . . . . . . . 6 4.1. The Version Sub-Field . . . . . . . . . . . . . . . . . . 6
4.2. The Reserved Sub-Field . . . . . . . . . . . . . . . . . 6 4.2. The Reserved Sub-Field . . . . . . . . . . . . . . . . . 6
4.3. The Timestamp Sub-Field . . . . . . . . . . . . . . . . . 6 4.3. The Timestamp Sub-Field . . . . . . . . . . . . . . . . . 6
4.4. The Hash Sub-Field . . . . . . . . . . . . . . . . . . . 6 4.4. The Hash Sub-Field . . . . . . . . . . . . . . . . . . . 6
5. Updating the Server Secret . . . . . . . . . . . . . . . . . 7 5. Updating the Server Secret . . . . . . . . . . . . . . . . . 7
6. Cookie Algorithms . . . . . . . . . . . . . . . . . . . . . . 8 6. Cookie Algorithms . . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 8. Security and Privacy Considerations . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10 9.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix B. Test vectors . . . . . . . . . . . . . . . . . . . . 10 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 11
B.1. Learning a new Server Cookie . . . . . . . . . . . . . . 10 Appendix B. Test vectors . . . . . . . . . . . . . . . . . . . . 11
B.2. The same client learning a renewed (fresh) Server Cookie 11 B.1. Learning a new Server Cookie . . . . . . . . . . . . . . 11
B.3. Another client learning a renewed Server Cookie . . . . . 12 B.2. The same client learning a renewed (fresh) Server Cookie 12
B.4. IPv6 query with rolled over secret . . . . . . . . . . . 13 B.3. Another client learning a renewed Server Cookie . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 B.4. IPv6 query with rolled over secret . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
DNS cookies, as specified in [RFC7873], are a lightweight DNS DNS cookies, as specified in [RFC7873], are a lightweight DNS
transaction security mechanism that provides limited protection to transaction security mechanism that provides limited protection to
DNS servers and clients against a variety of denial-of-service and DNS servers and clients against a variety of denial-of-service and
amplification, forgery, or cache poisoning attacks by off-path amplification, forgery, or cache poisoning attacks by off-path
attackers. This document specifies a means of producing attackers. This document specifies a means of producing
interoperable strong cookies so that an anycast server set including interoperable strong cookies so that an anycast server set including
diverse implementations can be easily configured to interoperate with diverse implementations can be easily configured to interoperate with
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In Section Section 5 instructions on updating Server Secrets are In Section Section 5 instructions on updating Server Secrets are
given. given.
In Section Section 6 the different hash functions usable for DNS In Section Section 6 the different hash functions usable for DNS
Cookie construction are listed. [FNV] and HMAC-SHA-256-64 [RFC6234] Cookie construction are listed. [FNV] and HMAC-SHA-256-64 [RFC6234]
are deprecated and [SipHash-2.4] is introduced as a REQUIRED hash are deprecated and [SipHash-2.4] is introduced as a REQUIRED hash
function for server side DNS Cookie implementations. function for server side DNS Cookie implementations.
IANA considerations are in Section 7. IANA considerations are in Section 7.
Privacy and Security Considerations in Section 8.
Acknowledgements are in Appendix A. Acknowledgements are in Appendix A.
Test vectors are in Appendix B. Test vectors are in Appendix B.
1.2. Definitions 1.2. Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "*NOT RECOMMENDED*", "MAY", "SHOULD", "SHOULD NOT", "RECOMMENDED", "*NOT RECOMMENDED*", "MAY",
and "OPTIONAL" in this document are to be interpreted as described in and "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
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specification in Section 4 of this document, which MUST be used by specification in Section 4 of this document, which MUST be used by
Server Cookie implementations. Server Cookie implementations.
This document has suggestions on Client Cookie construction in This document has suggestions on Client Cookie construction in
Section 3. The previous example in Appendix A.2 of [RFC7873] is NOT Section 3. The previous example in Appendix A.2 of [RFC7873] is NOT
RECOMMENDED. RECOMMENDED.
3. Constructing a Client Cookie 3. Constructing a Client Cookie
The Client Cookie is a cryptographic nonce and should be treated as The Client Cookie is a cryptographic nonce and should be treated as
such. For simplicity, it can be calculated from Server IP Address, such. It is RECOMMENDED to create a new Client Cookie for each new
and a Client Secret known only to the Client that is changed whenever upstream server a Client connects to. The Client Cookie SHOULD have
an IP address previously used by the Client is no longer available. at least 64-bits of entropy.
The Client Cookie SHOULD have at least 64-bits of entropy.
Except for when the Client IP address changes, there is no need to When a Server does not support DNS Cookies, the Client MUST NOT send
change the Client Secret often if a secure pseudorandom function the same Client Cookie to that same Server again. Instead, it is
(like [SipHash-2.4]) is used. It is reasonable to change the Client recommended that the Client does not send a Client Cookie to that
secret then only if it has been compromised or after a relatively Server for a certain period, like for example five minutes, before it
long period of time such as no longer than a year. retries with a new Client Cookie.
It is RECOMMENDED but not required that the following pseudorandom When a Server does support DNS Cookies, the Client should store the
function be used to construct the Client Cookie: Client Cookie alongside the Server Cookie it registered for that
Server.
Client-Cookie = MAC_Algorithm( Except for when the Client IP address changes, there is no need to
Server IP Address, Client Secret ) change the Client Cookie often. It is reasonable to change the
Client Cookie then only if it has been compromised or after a
relatively long period of time such as no longer than a year. Client
Cookies are not expected to survive a program restart.
Client-Cookie = 64 bits of entropy
Previously, the recommended algorithm to compute the Client Cookie Previously, the recommended algorithm to compute the Client Cookie
included Client IP Address as an input to the MAC_Algorithm. included Client IP Address as an input to a hashing function.
However, when implementing the DNS Cookies, several DNS vendors found However, when implementing the DNS Cookies, several DNS vendors found
impractical to include the Client IP as the Client Cookie is impractical to include the Client IP as the Client Cookie is
typically computed before the Client IP address is known. Therefore, typically computed before the Client IP address is known. Therefore,
the requirement to put Client IP address as input was removed. the requirement to put Client IP address as input was removed.
However, for privacy reasons, in order to prevent tracking of devices However, for privacy reasons, in order to prevent tracking of devices
across links and to not circumvent IPv6 Privacy Extensions [RFC4941], across links and to not circumvent IPv6 Privacy Extensions [RFC4941],
Clients MUST NOT re-use a Client or Server Cookie after the Client IP Clients MUST NOT re-use a Client or Server Cookie after the Client IP
address has changed. address has changed.
The Client IP address is available on the UDP socket when it receives One way to track Client IP addresses, is to register the Client IP
the Server Cookie and should be registered alongside the Server address alongside the Server Cookie when it receives the Server
Cookie. In subsequent queries to the Server with that Server Cookie, Cookie. In subsequent queries to the Server with that Server Cookie,
the socket MUST be bound to the Client IP address that was also used the socket MAY be bound to the Client IP address that was also used
(and registered) when it received the Server Cookie. Failure to bind (and registered) when it received the Server Cookie. Failure to bind
must result in a new Client Cookie, which, for the method described MUST then result in a new Client Cookie.
in this section means a new Client Secret.
4. Constructing a Server Cookie 4. Constructing a Server Cookie
The Server Cookie is effectively a Message Authentication Code (MAC) The Server Cookie is effectively a Message Authentication Code (MAC)
and should be treated as such. The Server Cookie is calculated from and should be treated as such. The Server Cookie is calculated from
the Client Cookie, a series of Sub-Fields specified below, the Client the Client Cookie, a series of Sub-Fields specified below, the Client
IP address, and a Server Secret known only to the servers responding IP address, and a Server Secret known only to the servers responding
on the same address in an anycast set. on the same address in an anycast set.
Changing the Server Secret regularly is RECOMMENDED but, when a Changing the Server Secret regularly is RECOMMENDED but, when a
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+---------+-------+---------------------------------------+ +---------+-------+---------------------------------------+
| 0 | 8-32 | reserved | | 0 | 8-32 | reserved |
| 1 | 8-15 | unassiged | | 1 | 8-15 | unassiged |
| 1 | 16 | SipHash-2.4 [this document] Section 4 | | 1 | 16 | SipHash-2.4 [this document] Section 4 |
| 1 | 17-32 | unassigned | | 1 | 17-32 | unassigned |
| 2-239 | 8-32 | unassigned | | 2-239 | 8-32 | unassigned |
| 240-254 | 8-32 | private use | | 240-254 | 8-32 | private use |
| 255 | 8-32 | reserved | | 255 | 8-32 | reserved |
+---------+-------+---------------------------------------+ +---------+-------+---------------------------------------+
8. References 8. Security and Privacy Considerations
8.1. Normative References DNS Cookies provides limited protection to DNS servers and clients
against a variety of denial-of-service and amplification/forgery or
cache poisoning attacks by off-path attackers. They provide no
protection against on-path adversaries that can observe the plaintext
DNS traffic. An on-path adversary that can observe a Server Cookie
for a client and server interaction, can use that Server Cookie for
amplification and denial-of-service forgery attacks for the lifetime
of the Server Cookie.
In [RFC7873] it was RECOMMENDED to construct a Client Cookie by using
a pseudorandom function of the Client IP Address, the Server IP
Address, and a secret quantity known only to the client. The Client
IP Address was included to ensure that a client could not be tracked
if its IP Address changes due to privacy mechanisms or otherwise.
In this document, we changed Client Cookie construction to be just 64
bits of entropy newly created for each new upstream server the client
connects to. As a consequence additional care needs to be taken to
prevent tracking of clients. To prevent tracking, a new Client
Cookie for a server MUST be created whenever the Client IP Address
changes.
Unfortunately, tracking Client IP Address Changes is impractical with
servers that do not support DNS Cookies. To prevent tracking of
clients with non DNS Cookie supporting servers, a client MUST NOT
send a previously sent Client Cookie. To prevent the creation of a
new Client Cookie for each query to an non DNS Cookies supporting
server, it is RECOMMENDED to not send a Client Cookie to that server
for a certain period, like for example five minute.
Summarizing:
o In order to provide minimal authentication, a client MUST use a
different Client Cookie for each different Server IP Address.
o To prevent tracking of clients, a new Client Cookie MUST be
created when the Client IP Address changes.
o To prevent tracking of clients for a non DNS Cookie supporting
server, a client MUST NOT send a previously sent Client Cookie to
that server, unless it can track Client IP Address changes for
those servers too.
Besides the Client Cookie construction, this update on [RFC7873] does
not introduce any new characteristics to DNS Cookies operations and
the Security Considerations section of [RFC7873] still applies.
9. References
9.1. Normative References
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
DOI 10.17487/RFC1982, August 1996, DOI 10.17487/RFC1982, August 1996,
<https://www.rfc-editor.org/info/rfc1982>. <https://www.rfc-editor.org/info/rfc1982>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 9, line 42 skipping to change at page 10, line 45
<https://www.rfc-editor.org/info/rfc7873>. <https://www.rfc-editor.org/info/rfc7873>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[SipHash-2.4] [SipHash-2.4]
Aumasson, J. and D. Bernstein, "SipHash: a fast short- Aumasson, J. and D. Bernstein, "SipHash: a fast short-
input PRF", 2012, <https://131002.net/siphash/>. input PRF", 2012, <https://131002.net/siphash/>.
8.2. Informative References 9.2. Informative References
[FNV] Fowler, G., Noll, L., Vo, K., Eastlake, D., and T. Hansen, [FNV] Fowler, G., Noll, L., Vo, K., Eastlake, D., and T. Hansen,
"The FNV Non-Cryptographic Hash Algorithm", "The FNV Non-Cryptographic Hash Algorithm",
<https://datatracker.ietf.org/doc/draft-eastlake-fnv>. <https://datatracker.ietf.org/doc/draft-eastlake-fnv>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234, (SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011, DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>. <https://www.rfc-editor.org/info/rfc6234>.
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