Internet DRAFT - draft-rsalz-drbg-speck-wap-wep
draft-rsalz-drbg-speck-wap-wep
Network Working Group R. Salz
Internet-Draft Akamai Technologies
Intended status: Best Current Practice March 21, 2016
Expires: September 22, 2016
No MTI Crypto without Public Review
draft-rsalz-drbg-speck-wap-wep-00
Abstract
Cryptography is becoming more important to the IETF and its
protocols, and more IETF protocols are using, or looking at,
cryptography to increase privacy on the Internet [RFC7258].
This document specifies a proposed best practice for any protocol (or
data format) that uses cryptography. Namely, that such RFCs cannot
specify an algorithm as mandatory-to-implement (MTI) unless that
algorithm has had reasonable public review. This document also
"sketches out" a rough definition around what such a review would
look like.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 22, 2016.
Copyright Notice
Copyright (c) 2016 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Why is Cryptography Hard? . . . . . . . . . . . . . . . . . . 3
4. Things to avoid . . . . . . . . . . . . . . . . . . . . . . . 3
5. How to Do it Right . . . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
The term "snake oil" is used as a pejorative for something which
appears to do its job acceptably, but actually does not; see
https://en.wikipedia.org/wiki/Snake_oil_%28cryptography%29 . It is a
goal of the IETF that we never be mislead into being, or mistakenly
taken as, snake oil salesman.
2. Introduction
Cryptography is becoming more important to the IETF and its
protocols, and more IETF protocols are using, or looking at,
cryptography to increase privacy on the Internet [RFC7258].
This document specifies a proposed best practice for any protocol (or
data format) that uses cryptography. Namely, that such RFCs cannot
specify an algorithm as mandatory-to-implement (MTI) unless that
algorithm has had reasonable public review. This document also
"sketches out" a rough definition around what such a review would
look like.
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3. Why is Cryptography Hard?
Cryptography is hard because it is not like traditional IETF protocol
deployments. In this classic situation, if one one party implements
a protocol incorrectly, it usually becomes obvious as
interoperability suffers or completely fails. But with cryptography,
one party can have implementation defects, or known exploitable
weaknesses, that expose the entire communication stream to an
attacker. Open source and code reviews are not a panacea here, but
using only widely-accepted cryptographic mechanisms (e.g., avoiding
facilities like https://en.wikipedia.org/wiki/Dual_EC_DRBG ) will
reduce the attack surface.
Cryptography is hard because subtle design characteristics can have
disastrous consequences. For example, the US Digital Signatiure
Algorithm requires the random nonce to be protected and never re-
used. If those requirements are not met, the private key can be
leaked.
Cryptography is hard because adversaries design new attacks and
refine existing ones. Attacks get better over time; they never get
worse. For example, it is now de riguer to protect against CPU
timing attacks, even when the device is only viewable over a network.
A recent paper (XXX reference) can identify a private key if your
smartphone is just laid next to an innocuous charging device. We
understand power differential attacks, timing attacks, and perhaps
cache line attacks; we now have to think about RFI emissions from our
phone.
Cryptography is hard because the order of operations can matter. It
is not intuitively obvious to most developers, which should come
first among signing, compression and encryption. This issues was
first raised in Spring of 2001 ("Defective Sign & Encrpyt in S/MIME,
PKCS#7, MOSS, PEM, and XML" by Don Davis) but was only addressed in
TLS by [RFC7366] more than a dozen years later.
Getting the cryptography right is important because the Internet, and
therefore the work of the IETF, has become a tempting target for all
types of attackers, from individual "script kiddies," through
criminal commercial botnet and phishing ventures, up to national-
scale adversaries operating on behalf of their nation-state.
4. Things to avoid
"Sunlight is said to be the best of disinfectants; electric light the
most efficient policeman." - Louis Brandeis, _Other People's Money
and How Bankers Use it,_ first published as a set of articles in
_Harper's Weekly_.
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Cryptography that is developed in private, such as among an industry
consortium is a bad idea. Notable examples of this include:
o A5/1 and A5/2 for GSM-based mobile phones.
o WEP and WPA for WiFi access.
It is hard to get good public review of patented cryptography, unless
there is a strongly compelling need. For example, decades ago RSA
was the only practial public-key mechanism available. Part of the
concern about patented cryptography is that the patent-holder has
every incentive to provide that their system is good, while the rest
of the world generally has little interest in proving that their
commercial venture is bad. Examples of this include:
o Algebraic Eraser, presented at IETF-xx (XXX reference), and since
then has had a number of effective attacks.
o XXX MORE NEEDED
5. How to Do it Right
Cryptographic agility, [RFC7696], is probably a MUST. While it has
its detractors, there are no known (to the author) practical
considerations to evolving a deployed based to stronger crypto, while
still maintaining interoperability with existing entities. This
requires being able to make informed choices about when to use old
weak crypto, and when to use the "latest and greatest," and while not
much software, and essentially no end-users, are capable of making
that choice, it seems sadly the best we can do.
The second consideration is to avoid temptation and premature
optimization. Do not adopt an algorithm just because it seems "small
and fast" or comes from "someone I respect."
What constitutes sufficient public review? It is hard to say. An
open competition, such as those that led to AES (XXX ref) and SHA-3
(XXX ref) seem to be good, even when they come from sources that are
under widespread suspicion, like the US Government. These efforts,
like the Password Hashing Competition https://password-hashing.net/ ,
had wide international participation and analysis by many noted
exports.
Papers presented in the various Crypto conferences (XXX need list)
are good. Same for various Usenix workshops.
Proof by contest - "Nobody's Claimed my $200 reward" - are useless
for a number of reasons. They tend to be promoted by amateur
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cryptographers as a way to get attention, and if someone actually
looks at them they are always cracked. Numerical analysis is a
better approach, albeit much harder work.
6. Acknowledgements
Thanks to Stephen Farrell for instigating this.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
7.2. Informative References
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <http://www.rfc-editor.org/info/rfc7258>.
[RFC7366] Gutmann, P., "Encrypt-then-MAC for Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", RFC 7366, DOI 10.17487/RFC7366, September 2014,
<http://www.rfc-editor.org/info/rfc7366>.
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<http://www.rfc-editor.org/info/rfc7696>.
Author's Address
Rich Salz
Akamai Technologies
Email: rsalz@akamai.com
Salz Expires September 22, 2016 [Page 5]
