Network Working Group K. Moore
Internet-Draft Network Heretics
Intended status: Best Current Practice R. Barnes
Expires: May 4, 2017 Mozilla
H. Tschofenig
ARM Limited
October 31, 2016
Best Current Practices for Securing Internet of Things (IoT) Devices
draft-moore-iot-security-bcp-00.txt
Abstract
In recent years, embedded computing devices have increasingly been
provided with Internet interfaces, and the typically-weak network
security of such devices has become a challenge for the Internet
infrastructure. This document lists a number of minimum requirements
that vendors of Internet of Things (IoT) devices need to take into
account during development and when producing firmware updates, in
order to reduce the frequency and severity of security incidents in
which such devices are implicated.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 4, 2017.
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
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Note about version -00 of this document . . . . . . . . . 5
2. Design Considerations . . . . . . . . . . . . . . . . . . . . 5
2.1. General security design considerations . . . . . . . . . 5
2.1.1. Threat analysis . . . . . . . . . . . . . . . . . . . 6
2.1.2. Use of Standard Cryptographic Algorithms . . . . . . 6
2.1.3. Use of Standard Security Protocols . . . . . . . . . 6
2.1.4. Security protocols should support algorithm agility . 7
2.2. Authentication requirements . . . . . . . . . . . . . . . 7
2.2.1. Resistance to keyspace-searching attacks . . . . . . 7
2.2.2. Protection of authentication credentials . . . . . . 7
2.2.3. Resistance to authentication DoS attacks . . . . . . 8
2.2.4. Unauthenticated device use disabled by default . . . 8
2.2.5. Per-device unique authentication credentials . . . . 8
2.3. Encryption Requirements . . . . . . . . . . . . . . . . . 8
2.3.1. Encryption should be supported . . . . . . . . . . . 8
2.3.2. Opportunistic encryption discouraged . . . . . . . . 9
2.3.3. Encryption algorithm strength . . . . . . . . . . . . 9
2.3.4. Man in the middle attack . . . . . . . . . . . . . . 9
2.4. Firmware Updates . . . . . . . . . . . . . . . . . . . . 9
2.4.1. Automatic update capability . . . . . . . . . . . . . 9
2.4.2. Enable automatic firmware update by default . . . . . 9
2.4.3. Backward compatibility of firmware updates . . . . . 10
2.4.4. Automatic updates should be phased in . . . . . . . . 10
2.4.5. Authentication of firmware updates . . . . . . . . . 10
2.5. Private key management . . . . . . . . . . . . . . . . . 10
2.6. Operating system features . . . . . . . . . . . . . . . . 10
2.6.1. Use of memory compartmentalization . . . . . . . . . 10
2.6.2. Privilege minimization . . . . . . . . . . . . . . . 11
2.7. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . 11
3. Implementation Considerations . . . . . . . . . . . . . . . . 11
3.1. Randomness . . . . . . . . . . . . . . . . . . . . . . . 11
4. Firmware Development Practices . . . . . . . . . . . . . . . 11
5. Documentation and Support Practices . . . . . . . . . . . . . 12
5.1. Support Commitment . . . . . . . . . . . . . . . . . . . 12
5.2. Bug Reporting . . . . . . . . . . . . . . . . . . . . . . 12
5.3. Labeling . . . . . . . . . . . . . . . . . . . . . . . . 12
5.4. Documentation . . . . . . . . . . . . . . . . . . . . . . 13
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6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
The weak security of Internet of Things devices has resulted in many
well-publicized security incidents over the last few years.
Unfortunately, it appears that very few lessons have been learned
from those incidents. The rate at which IoT devices are compromised
via network-based attacks appears to be increasing. The effect of
such security breaches goes far beyond the immediate effect on the
compromised devices and their users. A compromised device may, for
example, expose to an attacker secrets (such as passwords) stored in
the device. A compromised device also may be used to attack other
computers on the same local network as the device, or elsewhere on
the Internet. Attackers have constructed application networks of
compromised devices which have then been used for the purpose of
attacking other network hosts and services, for example distributed
password guessing attacks and distributed denial of service (DDoS)
attacks. [SNMP-DDOS][DDOS-KREBS] This document recommends a small
number of minimum security requirements to reduce some of the more
easily prevented security problems.
The scope of these recommendations is as follows:
- These measures described in this document are intended to impede
network-based attacks. These measures are not intended to impede
other kinds of attacks, e.g. those requiring physical access to
the device, though following these requirements may help reduce
the effectiveness of some such attacks. This document does not
address physical attacks because thwarting such attacks is
generally outside of IETF's expertise, and because it is
understood that the physical security requirements of Internet-
connected devices vary widely from one application to another.
However, because a device compromised by physical means may be
used to attack other devices or to obtain information that useful
in attacking other devices, it is strongly recommended that
vendors of Internet-connected devices carefully consider physical
security requirements when designing their products.
- In principle these requirements apply to all hosts that connect to
the Internet, but this list of requirements is specifically
targeted at devices that are constrained in their capabilities,
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more than general-purpose programmable hosts (PCs, servers,
laptops, tablets, etc.), routers, middleboxes, etc. While this is
a fuzzy boundary, it reflects the current understanding of IoT. A
more detailed treatment of some of the constraints of IoT devices
can be found in [RFC7228].
- These are MINIMUM requirements that apply to all devices. They
are unlikely to be sufficient by themselves, to ensure security of
hosts from attack. Because IoT devices are used in a large number
of different domains with different needs, each device will have
its own unique security considerations. It is not feasible to
completely list all security requirements in a document such as
this. Vendors should conduct threat assessments of each device
they produce, to determine which additional security
considerations are applicable for use in a given application
domain.
- It is expected that this list of requirements will be revised from
time to time, as new threats are identified, and/or new security
techniques become feasible.
- This document makes broad recommendations, but avoids recommending
specific technological solutions to security issues. A companion
document may be produced with suggestions for design choices and
implementations that may aid in meeting these requirements.
We expect that many of the requirements can easily be met by most
vendors, but may require additional documentation and transparency of
a vendor's development practices to improve credibility of their
security practices in the marketplace.
1.1. 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 RFC
2119 [RFC2119]. These key words describe normative requirements of
this specification. This specification also contains non-normative
recommendations that do not use these key words.
This document uses the term "firmware" to refer to the executable
code and associated data that, in combination with device hardware,
implements the functionality of an internet- connected device.
Traditionally the term "firmware" refers to code and data stored in
non-volatile memory as distinguished from "software" which presumably
refers to code stored in read/write or erasable memory, or code that
can be loaded from other devices. For the purpose of this document,
"firmware" applies to any kind of code or data that implements the
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functions that the device provides. Both software and firmware
present similar issues regarding device security, and it is easier to
use "firmware" consistently than to write "software and firmware".
1.2. Note about version -00 of this document
The goal for the initial version of this document is to invite
discussion about what minimum security standards for internet-
connected devices are appropriate. Consequently, this draft suggests
a wide range of potential measures. The authors, however, understand
that imposing too many barriers to adoption might discourage device
manufacturers from attempting to comply with this standard. We seek
to find the right balance that helps improve the security of the
Internet. We understand that some of the requirements in this draft
may need to be removed or relaxed, at least in an initial version of
a BCP document, and that other requirements may require additional
refinement and justification.
2. Design Considerations
This section lists requirements and considerations that should affect
the design of an internet-connected device. Broadly speaking, such
considerations include device architecture, hardware and firmware
component choices, partitioning of function, design and/or choice of
protocols used to communicate with the device.
2.1. General security design considerations
In general an Internet connected device should:
- Protect itself from attacks that impair its function or allow it
to be used for unintended purposes without authorization;
- Protect its private authentication credentials and key material
from disclosure to unauthorized parties;
- Protect the information received from the device, transmitted from
the device, or stored on the device, from inappropriate disclosure
to unauthorized parties; and
- Protect itself from being used as a vector to attack other devices
or hosts on the Internet.
Each device is responsible for its own security and for ensuring that
it is not used as a vector for attack on other Internet hosts. The
design of a device MUST NOT assume that a firewall or other perimeter
security measure will protect the device from attack. While useful
as part of a layered defense strategy, perimeter security has
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consistently been demonstrated to be insufficient to thwart attacks
by itself. There are nearly always mechanisms by which one or more
hosts on the local network can be compromised, and which in turn can
serve as a means to attack other hosts. Even "air gapped" networks
have been compromised by portable storage devices or software
updates.
For some kinds of attack, there is a limited amout that a device can
do to prevent the attack. For instance, any device can fall victim
to certain kinds of denial-of-service attack caused by receiving more
traffic in a given amount of time than the device can process. A
device should be designed to gracefully tolerate some amount of
excessive traffic without failing entirely, but at some point the
device receives so much traffic that it cannot distinguish valid
requests from invalid ones.
2.1.1. Threat analysis
The design for a device MUST enumerate specific security threats
considered in its design, and the specific measures taken (if any) to
remedy or limit the effect of each threat. This requirement
encourages making deliberate, explicit choices about security
measures at design time rather than leaving security as an
afterthought. This document is also useful later in the life cycle
of a device if it becomes necessary to improve security; for instance
it can help identify whether the original design choices fulfilled
their intended function or failed to do so, or whether a newly
discovered threat was not anticipated in the original design.
2.1.2. Use of Standard Cryptographic Algorithms
Standard or well-established, mature algorithms for cryptographic
functions (such as symmetric encryption, public-key encryption,
digital signatures, cryptographic hash / message integrity check)
MUST be used.
Explanation: A tremendous amount of subtlety must be understood in
order to construct cryptographic algorithms that are resistant to
attack. A very few people in the world have the knowledge required
to construct or analyze robust new cryptographic algorithms, and even
then, many knowledgable people have constructed algorithms that were
found to be flawed within a short time.
2.1.3. Use of Standard Security Protocols
Standard protocols for authentication, encryption, and other means of
assuring security SHOULD be used whenever apparently-robust,
applicable protocols exist.
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Explanation: The amount of expertise required to design robust
security protocols is comperable to that required to design robust
cryptographic algorithms. However, there are sometimes use cases for
which no existing standard protocol may be suitable. In these cases
it may be necessary to adapt an existing protocol for a new use case,
or even to design a new security protocol.
2.1.4. Security protocols should support algorithm agility
The security protocols chosen for a device design, and the
implementations of those protocols, SHOULD support the ability to
choose between multiple cryptographic algorithms and/or to negotiate
minimum key sizes.
Explanation: This way, if a flaw in one algorithm is discovered that
weakens its security, updated devices or their application peers with
which they communicate, may refuse to use that algorithm, or permit
its use only with a longer key than originally required. This allows
devices and protocol implementations to continue providing adequate
security even after weaknesses in algorithms are discovered.
The concept of crypto agility is further described in [RFC7696].
2.2. Authentication requirements
The vast majority of Internet-connected devices will require
authentication for some purposes, whether to protect the device from
unauthorized use or reconfiguration, and to protect information
stored within the device from disclosure or modification. This
section details authentication requirements for devices that require
authentication.
2.2.1. Resistance to keyspace-searching attacks
A device that requires authentication MUST be designed to make brute-
force authentication attacks, dictionary attacks, or other attacks
that involve exhaustive searching of the device's key or password
space, infeasible.
2.2.2. Protection of authentication credentials
A device MUST be designed to protect any secrets used to authenticate
to the device (such as passwords or private keys) from disclosure via
monitoring of network traffic to or from the device. For example, if
a password is used to authenticate a client to the device, that
password must not appear "in the clear" or in any form via which
extraction of the password from network traffic is computationally
feasible.
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2.2.3. Resistance to authentication DoS attacks
A device SHOULD be designed to gracefully tolerate excessive numbers
of authentication attempts, for instance by giving CPU priority to
existing protocol sessions that have already successfully
authenticated, limiting the number of concurrent new sessions in the
process of authenticating, and randomly discarding attempts to
establish new sessions beyond that limit. The specific mechanism is
a design choice to be made in light of the specific function of the
device and the protocols used by the device. What's important for
this requirement is that this be an explicit choice.
2.2.4. Unauthenticated device use disabled by default
A device that supports authentication SHOULD NOT be shipped in a
condition that allows an unauthenticated client to use any function
of the device that requires authentication, or to change that
device's authentication credentials.
Explanation: Most devices that can be used in an unauthenticated
state will never be configured to require authentication. These
devices are attractive targets for attack and compromise, especially
by botnets. This is very similar to the problems caused by shipping
devices with default passwords.
2.2.5. Per-device unique authentication credentials
Many devices that require authentication will be shipped with default
authentication credentials, so that the customer can authenticate to
the device using those credentials until they are changed. Each
device that requires authentication SHOULD be instantiated either
prior to shipping, or on initial configuration by the user, with
credentials unique to that device. If a device is not instantiated
with device-unique credentials, that device MUST NOT permit normal
operation until those credentials have been changed to something
other than the default credentials.
Explanation: devices that were shipped with default passwords have
been implicated in several serious denial-of-service attacks on
widely-used Internet services.
2.3. Encryption Requirements
2.3.1. Encryption should be supported
Internet-connected devices SHOULD support the capability to encrypt
traffic sent to or from the device. Any information transmitted over
a network is potentially sensitive to some customers. For example,
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even a home temperature monitoring sensor may reveal information
about when occupants are away from home, when they wake up and when
they go to bed, when and how often they cook meals - all of which are
useful to, say, a thief.
Note: This requirement is separate from the requirement to protect
authentication secrets from disclosure. Authentication secrets MUST
be protected from disclosure even if a general encryption capability
is not supported, or if the capability is optional and a particular
client or user doesn't use it.
2.3.2. Opportunistic encryption discouraged
If a device supports encryption and use of encryption is optional,
the device SHOULD be configurable to require encryption.
2.3.3. Encryption algorithm strength
Encryption algorithms and minimum key lengths SHOULD be chosen to
make brute-force attack infeasible.
2.3.4. Man in the middle attack
Encryption protocols SHOULD be resistant to man-in-the-middle attack.
2.4. Firmware Updates
2.4.1. Automatic update capability
Vendors MUST offer an automatic firmware update mechanism. A
discussion about the firmware update mechanisms can be found in
[I-D.iab-iotsu-workshop].
Devices SHOULD be configured to check for the existence of firmware
updates at frequent but irregular intervals.
2.4.2. Enable automatic firmware update by default
Automatic firmware updates SHOULD be enabled by default. A device
MAY offer an option to disable automatic firmware updates. If
enabling or disabling the automatic update feature is controlled by a
network protocol, the device MUST require authentication of any
request to enable or disable it.
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2.4.3. Backward compatibility of firmware updates
Automatic firmware updates SHOULD NOT change network protocol
interfaces in any way that is incompatible with previous versions. A
vendor MAY offer firmware updates which add new features as long as
those updates are not automatically initiated.
2.4.4. Automatic updates should be phased in
To prevent widespread simultaneous failure of all instances of a
particular kind of device due to a bug in a new firmware release,
automatic firmware updates SHOULD be phased-in over a short time
interval rather than updating all devices at once.
2.4.5. Authentication of firmware updates
Firmware updates MUST be authenticated and the integrity of such
updates assured before the update is installed. Unauthenticated
updates or updates where the authentication or integrity checking
fails MUST be rejected.
2.5. Private key management
If private key cryptography is used in a device's security protocols,
each device MUST be instantiated with its own unique private key or
keys. In many cases it will be necessary for the vendor to sign such
keys or arrange for them to be signed by a trusted party, prior to
shipping the device.
Per-device private keys SHOULD be generated on the device and never
exposed outside the device.
2.6. Operating system features
2.6.1. Use of memory compartmentalization
Device firmware SHOULD be designed to use hardware and operating
systems that implement memory compartmentalization techniques, in
order to prevent read, write, and/or execute access to areas of
memory by processes not authorized to use those areas for those
purposes.
Vendors that do not make use of such features MUST document their
design rationale.
Explanation: Such mechanisms, when properly used, reduce the impact
of a firmware bug, such as a buffer overflow vulnerability.
Operating systems, or even firmware running on "bare metal", that do
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not provide such a separation allow an attacker to gain access to the
complete address space. While these concepts have been available in
hardware for a long time already, they often are not utilized by
real-time operating systems.
2.6.2. Privilege minimization
Device firmware SHOULD be designed to isolate privileged code and
data from portions of the firmware that do not need to access them,
in order to minimize the potential for compromised code to access
those code and/or data.
2.7. Miscellaneous
3. Implementation Considerations
This section lists requirements for implementation that broadly
affect security of a device.
3.1. Randomness
Vendors MUST include a solution for generating cryptographic quality
random numbers in their products. Randomness is an important
component in security protocols and without such randomness many of
today's security protocols offer weak or no security protection.
Hardware random-number generators, when feasible, SHOULD be utilized,
but MAY be combined with other sources of randomness.
A discussion about randomness can be found in [RFC4086].
4. Firmware Development Practices
This section outlines requirements for development of firmware that
is employed on Internet-connected devices.
Vendors SHOULD use modern firmware development practices, including:
- Source code change control systems, which record all changes made
to source code along with the identity of the person who committed
the change. Such systems help to identify which versions of code
contain a particular bug, as well as protect against insertion of
malicious code.
- Bug tracking systems.
- Automated testing of a set of pre-defined test conditions,
including tests for all security vulnerabilities identified to
date via either analysis or experience.
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- Periodic checking of bug databases for reported security issues
associated with the product itself, and with all components (for
example: kernel, libraries, and protocol servers) used in the
product.
- Periodic checking of third party-provided source code and object
code for security bugs, or updates intended to thwart security
bugs.
All known security bugs for which fixes are known MUST be addressed
prior to shipping a new product or or a code update.
5. Documentation and Support Practices
5.1. Support Commitment
Vendors MUST be transparent about their commitment to supply devices
with updates before selling products to their customers and what
happens with those devices after the support period finishes.
Within the support period, vendors SHOULD provide firmware updates
whenever new security risks associated with their products are
identified. Such firmware updates SHOULD NOT change the protocol
interfaces to those products, except as necessary to address security
issues, so that they can be deployed without disruption to customers'
networks. Firmware updates MAY introduce new features which change
protocol interfaces if those features are optional and disabled by
default.
5.2. Bug Reporting
Vendors MUST provide an easy to find way for reporting of security
bugs, which is free of charge.
5.3. Labeling
Vendors MUST have a manufacturer, model number and hardware revision
number legibly printed on the device. This attempts to help
customers with bug reporting.
There SHOULD be a documented means of querying a device for its model
number, hardware revision number, and firmware revision number via
its network interface and/or via any manual input and display. This
interface MAY require authentication.
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5.4. Documentation
Vendors MUST offer documentation about their products so that
security experts are able to assess the design choices. While such a
document will not directly help end customers since they will almost
always lack the expertise to judge these design decisions but they
help security experts to assess liability and independent third
parties to compare products without spending an unproportional amount
of time.
This form of public documentation will help transparency similar to
other documentation requirements found in other industries. It will
also help to evolve the best practices described in this document.
6. Security Considerations
This entire document is about security.
7. IANA Considerations
This document does not contain any requests to IANA.
8. Acknowledgements
Add acknowledgements here.
9. References
9.1. 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>.
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<http://www.rfc-editor.org/info/rfc4086>.
9.2. Informative References
[DDOS-KREBS]
Goodin, D., "Record-breaking DDoS reportedly delivered by
>145k hacked cameras", September 2016,
<http://arstechnica.com/security/2016/09/botnet-of-145k-
cameras-reportedly-deliver-internets-biggest-ddos-ever/>.
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[I-D.iab-iotsu-workshop]
Tschofenig, H. and S. Farrell, "Report from the Internet
of Things (IoT) Software Update (IoTSU) Workshop 2016",
draft-iab-iotsu-workshop-00 (work in progress), October
2016.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.
[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>.
[SNMP-DDOS]
BITAG, "SNMP Reflected Amplification DDoS Attack
Mitigation", August 2012,
<https://www.bitag.org/documents/SNMP-Reflected-
Amplification-DDoS-Attack-Mitigation.pdf>.
Authors' Addresses
Keith Moore
Network Heretics
PO Box 1934
Knoxville, TN 37901
United States
EMail: moore@network-heretics.com
Richard Barnes
Mozilla
EMail: rbarnes@mozilla.com
Hannes Tschofenig
ARM Limited
EMail: hannes.tschofenig@gmx.net
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