Padding Policies for Extension Mechanisms for DNS (EDNS(0))
RFC 8467
Internet Engineering Task Force (IETF) A. Mayrhofer
Request for Comments: 8467 nic.at GmbH
Category: Experimental October 2018
ISSN: 2070-1721
Padding Policies for Extension Mechanisms for DNS (EDNS(0))
Abstract
RFC 7830 specifies the "Padding" option for Extension Mechanisms for
DNS (EDNS(0)) but does not specify the actual padding length for
specific applications. This memo lists the possible options
("padding policies"), discusses the implications of each option, and
provides a recommended (experimental) option.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). It represents the consensus of the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are candidates for any level of
Internet Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8467.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Mayrhofer Experimental [Page 1]
RFC 8467 Padding Policies for EDNS(0) October 2018
Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................2
3. General Guidance ................................................3
4. Padding Strategies ..............................................3
4.1. Recommended Strategy: Block-Length Padding .................3
4.2. Other Strategies ...........................................5
4.2.1. Maximal-Length Padding ..............................5
4.2.2. Random-Length Padding ...............................5
4.2.3. Random-Block-Length Padding .........................6
5. IANA Considerations .............................................6
6. Security Considerations .........................................6
7. References ......................................................7
7.1. Normative References .......................................7
7.2. Informative References .....................................7
Appendix A. Padding Policies That Are Not Sensible ................8
A.1. No Padding .................................................8
A.2. Fixed-Length Padding .......................................8
Acknowledgements ...................................................9
Author's Address ...................................................9
1. Introduction
[RFC7830] specifies the Extension Mechanisms for DNS (EDNS(0))
"Padding" option, which allows DNS clients and servers to
artificially increase the size of a DNS message by a variable number
of bytes, hampering size-based correlation of encrypted DNS messages.
However, RFC 7830 deliberately does not specify the actual length of
padding to be used. This memo discusses options regarding the actual
size of padding, lists advantages and disadvantages of each of these
"padding strategies", and provides a recommended (experimental)
strategy.
Padding DNS messages is useful only when transport is encrypted using
protocols such as DNS over Transport Layer Security [RFC7858], DNS
over Datagram Transport Layer Security [RFC8094], or other encrypted
DNS transports specified in the future.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Mayrhofer Experimental [Page 2]
RFC 8467 Padding Policies for EDNS(0) October 2018
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