draft-ietf-dprive-edns0-padding-03.txt   rfc7830.txt 
Network Working Group A. Mayrhofer Internet Engineering Task Force (IETF) A. Mayrhofer
Internet-Draft nic.at GmbH Request for Comments: 7830 nic.at GmbH
Intended status: Standards Track March 6, 2016 Category: Standards Track May 2016
Expires: September 7, 2016 ISSN: 2070-1721
The EDNS(0) Padding Option The EDNS(0) Padding Option
draft-ietf-dprive-edns0-padding-03
Abstract Abstract
This document specifies the EDNS(0) 'Padding' option, which allows This document specifies the EDNS(0) "Padding" option, which allows
DNS clients and servers to pad request and response messages by a DNS clients and servers to pad request and response messages by a
variable number of octets. variable number of octets.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79.
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Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. The 'Padding' Option . . . . . . . . . . . . . . . . . . . . 3 3. The "Padding" Option . . . . . . . . . . . . . . . . . . . . 3
4. Usage Considerations . . . . . . . . . . . . . . . . . . . . 3 4. Usage Considerations . . . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
8. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 7.1. Normative References . . . . . . . . . . . . . . . . . . 4
8.1. draft-ietf-dprive-edns0-padding-03 . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . 5
8.2. draft-ietf-dprive-edns0-padding-02 . . . . . . . . . . . 5 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 5
8.3. draft-ietf-dprive-edns0-padding-01 . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
8.4. draft-ieft-dprive-edns0-padding-00 . . . . . . . . . . . 5
8.5. draft-mayrhofer-edns0-padding-01 . . . . . . . . . . . . 5
8.6. draft-mayrhofer-edns0-padding-00 . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
The Domain Name System (DNS) [RFC1035] was specified to transport DNS The Domain Name System (DNS) [RFC1035] was specified to transport DNS
messages in clear text form. Since this can expose significant messages in cleartext form. Since this can expose significant
amounts of information about the internet activities of an end user, amounts of information about the Internet activities of an end user,
the IETF has undertaken work to provide confidentiality to DNS the IETF has undertaken work to provide confidentiality to DNS
transactions (see the DPRIVE WG). Encrypting the DNS transport is transactions (see the DPRIVE working group). Encrypting the DNS
considered as one of the options to improve the situation. transport is considered one of the options to improve the situation.
However, even if both DNS query and response messages were encrypted, However, even if both DNS query and response messages were encrypted,
meta data could still be used to correlate such messages with well metadata could still be used to correlate such messages with well-
known unencrypted messages, hence jeopardizing some of the known unencrypted messages, hence jeopardizing some of the
confidentiality gained by encryption. One such property is the confidentiality gained by encryption. One such property is the
message size. message size.
This document specifies the Extensions Mechanisms for DNS (EDNS(0)) This document specifies the Extensions Mechanisms for DNS (EDNS(0))
"Padding" Option, which allows to artificially increase the size of a "Padding" option, which allows DNS clients and servers to
DNS message by a variable number of bytes, hampering size-based artificially increase the size of a DNS message by a variable number
correlation of the encrypted message. of bytes, hampering size-based correlation of the encrypted message.
2. Terminology 2. Terminology
The terms "Requestor", "Responder" are to be interpreted as specified The terms "Requestor" and "Responder" are to be interpreted as
in [RFC6891]. specified in [RFC6891].
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", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
3. The 'Padding' Option 3. The "Padding" Option
The EDNS(0) [RFC6891] specifies a mechanism to include new options in The EDNS(0) [RFC6891] specifies a mechanism to include new options in
DNS packets, contained in the RDATA of the OPT meta-RR. This DNS packets, contained in the RDATA of the OPT meta-RR. This
document specifies the 'Padding' option in order to allow clients and document specifies the "Padding" option in order to allow clients and
servers pad DNS packets by a variable number of bytes. The 'Padding' servers to pad DNS packets by a variable number of bytes. The
option MUST occur at most once per OPT meta-RR (and hence, at most "Padding" option MUST occur at most, once per OPT meta-RR (and hence,
once per message). at most once per message).
The figure below specifies the structure of the option in the RDATA The figure below specifies the structure of the option in the RDATA
of the OPT RR: of the OPT RR:
0 8 16 0 8 16
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| OPTION-CODE | | OPTION-CODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| OPTION-LENGTH | | OPTION-LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| (PADDING) ... (PADDING) ... / | (PADDING) ... (PADDING) ... /
+- - - - - - - - - - - - - - - - +- - - - - - - - - - - - - - - -
Figure 1 Figure 1
The OPTION-CODE for the 'Padding' option is 12. The OPTION-CODE for the "Padding" option is 12.
The OPTION-LENGTH for the 'Padding' option is the size (in octets) of The OPTION-LENGTH for the "Padding" option is the size (in octets) of
the PADDING. The minimum number of padding octets is 0. the PADDING. The minimum number of PADDING octets is 0.
The PADDING octets SHOULD be set to 0x00. Other values MAY be used; The PADDING octets SHOULD be set to 0x00. Other values MAY be used,
for example, in cases where there is a concern that the padded for example, in cases where there is a concern that the padded
message could be subject to compression before encryption. PADDING message could be subject to compression before encryption. PADDING
octets of any value MUST be accepted in messages received. octets of any value MUST be accepted in the messages received.
4. Usage Considerations 4. Usage Considerations
This document does not specify the actual amount of padding to be This document does not specify the actual amount of padding to be
used, since this depends on the situation in which the option is used, since this depends on the situation in which the option is
used. However, padded DNS messages MUST NOT exceed the number of used. However, padded DNS messages MUST NOT exceed the number of
octets specified in the Requestor's Payload Size field encoded in the octets specified in the Requestor's Payload Size field encoded in the
RR Class Field (see Section 6.2.3 and 6.2.4 of [RFC6891]). RR Class Field (see Sections 6.2.3 and 6.2.4 of [RFC6891]).
Responders MUST pad DNS responses when the respective DNS query Responders MUST pad DNS responses when the respective DNS query
included the 'Padding' option, unless doing so would violate the included the "Padding" option, unless doing so would violate the
maximum UDP payload size. maximum UDP payload size.
Responders MAY pad DNS responses when the respective DNS query Responders MAY pad DNS responses when the respective DNS query
indicated EDNS(0) support of the Requestor and the 'Padding' option indicated EDNS(0) support of the Requestor and the "Padding" option
was not included. was not included.
Responders MUST NOT pad DNS responses when the respective DNS query Responders MUST NOT pad DNS responses when the respective DNS query
did not indicate EDNS(0) support. did not indicate EDNS(0) support.
5. IANA Considerations 5. IANA Considerations
IANA has assigned EDNS Option Code 12 for Padding. IANA has assigned Option Code 12 for "Padding" in the "DNS EDNS0
Option Codes (OPT)" registry.
IANA is requested to update the respective registration record by IANA has updated the respective registration record by changing the
changing the Reference field to [[THISRFC]] and the Status field to Reference field to RFC 7830 and the Status field to "Standard".
'Standard'.
6. Security Considerations 6. Security Considerations
Padding DNS packets obviously increases their size, and will Padding DNS packets obviously increases their size, and will
therefore lead to increased traffic. therefore lead to increased traffic.
The use of the EDNS(0) Padding only provides a benefit when DNS The use of the EDNS(0) padding only provides a benefit when DNS
packets are not transported in clear text. Further, it is possible packets are not transported in cleartext. Further, it is possible
EDNS(0) Padding may make DNS amplification attacks easier. that EDNS(0) padding may make DNS amplification attacks easier.
Implementations therefore MUST NOT use this option if the DNS Therefore, implementations MUST NOT use this option if the DNS
transport is not encrypted. transport is not encrypted.
Padding length might be affected by lower-level compression. Padding length might be affected by lower-level compression.
Therefore (as described in Section 3.3 of [RFC7525]), implementations Therefore (as described in Section 3.3 of [RFC7525]), implementations
and deployments SHOULD disable TLS-level compression. and deployments SHOULD disable compression at the Transport Layer
Security (TLS) level.
The payload of the 'Padding' option could (like many other fields in The payload of the "Padding" option could (like many other fields in
the DNS protocol) be used as a covert channel. the DNS protocol) be used as a covert channel.
7. Acknowledgements 7. References
This document was inspired by a discussion with Daniel Kahn Gillmor
during IETF93, as an alternative to the proposed padding on the TLS
layer. Allison Mankin, Andreas Gustafsson, Christian Huitema, Jinmei
Tatuya and Shane Kerr suggested text for this document.
8. Changes
Note to RFC Editors: Please remove this whole section before
publication
8.1. draft-ietf-dprive-edns0-padding-03
Fixed typo in Acknowledgements, added Shane. Do not use over
unencrypted transport is now a MUST. Logic around when responders
may send the option clarified. Reduced "hampering" claim in
introduction.
8.2. draft-ietf-dprive-edns0-padding-02
Clarified that changes section is to be removed before publication.
Clarified that both Requestors and Responders are to ignore padding
contents. changed text about non-zero padding contents based on WGLC
comments. removed security considerations about truncation based on
WGLC comment. added more acknowledgements. replaced "packets" with
"messages" where appropriate.
8.3. draft-ietf-dprive-edns0-padding-01
Fixed 'octects' typo. Changed 'covert channel' text to align with
allowing non-0x00 padding. changed IANA considerations - assigned
option code is 12. Changed field definitions to allow for non-0x00
padding, removed FORMERR requirement. referenced rfc7525 in security
considerations. added acknowledgements.
8.4. draft-ieft-dprive-edns0-padding-00
Adopted by WG. Changed text about message size limit based on
feedback.
8.5. draft-mayrhofer-edns0-padding-01
Changed minimum padding size to 0, rewrote Usage Considerations
section, extended Security considerations section
8.6. draft-mayrhofer-edns0-padding-00
Initial version
9. References
9.1. Normative References 7.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>. November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[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,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013, DOI 10.17487/RFC6891, April 2013,
<http://www.rfc-editor.org/info/rfc6891>. <http://www.rfc-editor.org/info/rfc6891>.
9.2. Informative References 7.2. Informative References
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <http://www.rfc-editor.org/info/rfc7525>. 2015, <http://www.rfc-editor.org/info/rfc7525>.
Acknowledgements
This document was inspired by a discussion with Daniel Kahn Gillmor
during IETF 93, as an alternative to the proposed padding on the TLS
layer. Allison Mankin, Andreas Gustafsson, Christian Huitema, Jinmei
Tatuya, and Shane Kerr suggested text for this document.
Author's Address Author's Address
Alexander Mayrhofer Alexander Mayrhofer
nic.at GmbH nic.at GmbH
Karlsplatz 1/2/9 Karlsplatz 1/2/9
Vienna 1010 Vienna 1010
Austria Austria
Email: alex.mayrhofer.ietf@gmail.com Email: alex.mayrhofer.ietf@gmail.com
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