IEC TS 62351-5:2009

Power systems management and associated information exchange - Data and communications security - Part 5: Security for IEC 60870-5 and derivatives

IEC/TS 62351-5:2009(E) specifies messages, procedures and algorithms for securing the operation of all protocols based on or derived from the standard IEC 60870-5: Telecontrol equipment and systems - Part 5: Transmission protocols. It more specifically applies to IEC 60870-5-101, IEC 60870-5-102, IEC 60870-5-103, IEC 60870-5-104.
This publication is of core relevance for Smart Grid.

General Information

• Status: Published
• Publication Date: 17-Aug-2009
• ICS: 33.200 - Telecontrol. Telemetering
• Technical Committee: TC 57 - Power systems management and associated information exchange
• Drafting Committee: WG 15 - TC 57/WG 15
• Current Stage: DELPUB - Deleted Publication
• Start Date: 29-Apr-2013
• Completion Date: 26-Oct-2025

Relations

• Revised: IEC TS 62351-5:2013 - Power systems management and associated information exchange - Data and communications security - Part 5: Security for IEC 60870-5 and derivatives
• Effective Date: 05-Sep-2023
• Revised: IEC 62351-5:2023 - Power systems management and associated information exchange - Data and communications security - Part 5: Security for IEC 60870-5 and derivatives
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC/TS 62351-5 ®
Edition 1.0 2009-08
TECHNICAL
SPECIFICATION
Power systems management and associated information exchange – Data and
communications security –
Part 5: Security for IEC 60870-5 and derivatives

IEC/TS 62351-5:2009(E)
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IEC/TS 62351-5 ®
Edition 1.0 2009-08
TECHNICAL
SPECIFICATION
Power systems management and associated information exchange – Data and
communications security –
Part 5: Security for IEC 60870-5 and derivatives

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XA
ICS 33.200 ISBN 978-2-88910-681-3
– 2 – TS 62351-5 © IEC:2009(E)
CONTENTS
FOREWORD.6
1 Scope and object.8
1.1 Scope.8
1.2 Intended audience and use .8
1.3 Items outside of scope .8
1.4 Use with other standards.8
1.5 Document organization and approach.9
1.6 Compliance .9
2 Normative references .9
3 Terms and definitions .10
4 Abbreviated terms .11
5 Problem description.11
5.1 Overview of clause .11
5.2 Specific threats addressed .11
5.3 Design issues.11
5.3.1 Overview of subclause.11
5.3.2 Asymmetric communications.11
5.3.3 Message-oriented.12
5.3.4 Poor sequence numbers or no sequence numbers.12
5.3.5 Limited processing power .12
5.3.6 Limited bandwidth.12
5.3.7 No access to authentication server .12
5.3.8 Limited frame length .13
5.3.9 Limited checksum.13
5.3.10 Radio systems.13
5.3.11 Dial-up systems.13
5.3.12 Variety of protocols affected .13
5.3.13 Differing data link layers .14
5.3.14 Long upgrade intervals .14
5.3.15 Remote sites .14
5.3.16 Multiple users .14
5.3.17 Unreliable media .14
5.4 General principles .14
5.4.1 Overview of subclause.14
5.4.2 Authentication only .14
5.4.3 Application layer only .15
5.4.4 Generic definition mapped onto different protocols .15
5.4.5 Bi-directional .15
5.4.6 Challenge-response.15
5.4.7 Pre-shared keys as default option.15
5.4.8 Backwards tolerance .15
5.4.9 Upgradeable.16
5.4.10 Perfect forward secrecy.16
5.4.11 Multiple users .16
6 Theory of operation (informative).16

TS 62351-5 © IEC:2009(E) – 3 –
6.1 Overview of clause .16
6.2 Narrative description .16
6.2.1 Basic concepts .16
6.2.2 Initiating the challenge.17
6.2.3 Replying to the challenge .17
6.2.4 Authenticating .17
6.2.5 Authentication failure.18
6.2.6 Aggressive mode.18
6.2.7 Changing keys.18
6.3 Example message sequences .19
6.3.1 Overview of subclause.19
6.3.2 Challenge of a critical ASDU .20
6.3.3 Aggressive mode.21
6.3.4 Initializing and changing session keys .22
6.4 State machine overview .23
7 Formal specification .25
7.1 Overview of clause .25
7.2 Message definitions.25
7.2.1 Distinction between messages and ASDUs.25
7.2.2 Challenge message .25
7.2.3 Reply message.27
7.2.4 Aggressive mode request .29
7.2.5 Key status request message.31
7.2.6 Key status message .31
7.2.7 Session key change message.34
7.2.8 Error message.36
7.3 Formal procedures .38
7.3.1 Overview of subclause.38
7.3.2 Challenger procedures .38
7.3.3 Responder procedures .48
7.3.4 Controlling station procedures .48
7.3.5 Controlled station procedures .53
8 Interoperability requirements .53
8.1 Overview of clause .53
8.2 Minimum requirements .53
8.2.1 Overview of subclause.53
8.2.2 HMAC algorithms .53
8.2.3 Key wrap algorithms .54
8.2.4 Fixed values .54
8.2.5 Configurable values.54
8.3 Options .55
8.3.1 Overview of subclause.55
8.3.2 HMAC algorithms .55
8.3.3 Encryption algorithms .55
8.3.4 Configurable values.56
9 Special applications.56
9.1 Overview of clause .56
9.2 Use with TCP/IP .56
9.3 Use with redundant channels.56

– 4 – TS 62351-5 © IEC:2009(E)
9.4 Use with external link encryptors .56
10 Requirements for referencing this specification.57
10.1 Overview of clause .57
10.2 Selected options.57
10.3 Operations considered critical .57
10.4 Addressing information.57
10.5 Message format mapping .57
10.6 Reference to procedures .57
11 Protocol implementation conformance statement .58
11.1 Overview of clause .58
11.2 Required algorithms .58
11.3 HMAC algorithms .58
11.4 Key wrap algorithms.58
11.5 Maximum error count.58
11.6 Use of error messages .58

Bibliography.59

Figure 1 – Example of successful challenge of critical ASDU .20
Figure 2 – Example of failed challenge of critical ASDU.20
Figure 3 – Example of a successful aggressive mode request.21
Figure 4 – Example of a failed aggressive mode request .21
Figure 5 – Example of session key initialization and periodic update.22
Figure 6 – Example of communications failure followed by session key change .23
Figure 7 – Major state transitions for controlling station .24
Figure 8 – Major state transitions for controlled station .25

Table 1 – Scope of application to standards.8
Table 2 – Summary of keys used .18
Table 3 – Challenge message.26
Table 4 – Reply message .28
Table 5 – Data included in the HMAC value calculation.29
Table 6 – Aggressive mode request message .29
Table 7 – Data included in the HMAC value calculation in aggressive mode .30
Table 8 – Key status request message .31
Table 9 – Use of default session keys.31
Table 10 – Key status message .32
Table 11 – Data included in the HMAC value calculation for key status.34
Table 12 – Key change message .34
Table 13 – Data included in the key wrap (in order) .35
Table 14 – Example of key order.35
Table 15 – Example of wrapped key data.36
Table 16 – Error message.36

TS 62351-5 © IEC:2009(E) – 5 –
Table 17 – States used in the state machine descriptions .38
Table 18 – Challenger state machine .41
Table 19 – Controlling station state machine.50

– 6 – TS 62351-5 © IEC:2009(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
POWER SYSTEMS MANAGEMENT AND ASSOCIATED INFORMATION
EXCHANGE – DATA AND COMMUNICATIONS SECURITY –

Part 5: Security for IEC 60870-5 and derivatives

FOREWORD
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The main task of IEC technical committees is to prepare International Standards. In
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• the required support cannot be obtained for the publication of an International Standard,
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• The subject is still under technical development or where, for any other reason, there is
the future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 62351-5, which is a technical specification, has been prepared by IEC technical
committee 57: Power systems management and associated information exchange.

TS 62351-5 © IEC:2009(E) – 7 –
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
57/861/DTS 57/921A/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 62351 series, under the general title: Power systems management
and associated information exchange – Data and communications security, can be found on
the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in the
data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The “colour inside” logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this publication using a colour printer.

– 8 – TS 62351-5 © IEC:2009(E)
POWER SYSTEMS MANAGEMENT AND ASSOCIATED INFORMATION
EXCHANGE – DATA AND COMMUNICATIONS SECURITY –

Part 5: Security for IEC 60870-5 and derivatives

1 Scope and object
1.1 Scope
This part of IEC 62351 specifies messages, procedures and algorithms for securing the
operation of all protocols based on or derived from the standard IEC 60870-5: Telecontrol
equipment and systems – Part 5: Transmission protocols. This specification applies to at least
those protocols listed in Table 1.
Table 1 – Scope of application to standards
Number Name
IEC 60870-5-101 Companion standard for basic telecontrol tasks
IEC 60870-5-102 Companion standard for the transmission of integrated totals in electric power systems
IEC 60870-5-103 Companions standard for the informative interface of protection equipment
IEC 60870-5-104 Network access for IEC 60870-5-101 using standard transport profiles
DNP3 Distributed Network Protocol (based on IEC 60870-1 through IEC 60870-5 and
controlled by the DNP Users Group)

1.2 Intended audience and use
The initial audience for this specification is intended to be the members of the working groups
developing the protocols listed in Table 1. For the measures described in this specification to
take effect, they must be accepted and referenced by the specifications for the protocols
themselves. This document is written to enable that process.
The subsequent audience for this specification is intended to be the developers of products
that implement these protocols.
Portions of this specification may also be of use to managers and executives in order to
understand the purpose and requirements of the work.
1.3 Items outside of scope
This part of IEC 62351 focuses only on application layer authentication and security issues
arising from such authentication, per directions from IEC Technical Committee 57 Working
Group 3. Other security concerns – in particular, protection from eavesdropping or man-in-
the-middle attacks through the use of encryption – are considered to be outside the scope.
Encryption may be added through the use of this specification with other specifications.
1.4 Use with other standards
Table 1 may issue standards to be
The working groups developing the protocols listed in
applied in conjunction with this specification. It is expected that these standards will describe
a mapping of this authentication mechanism to the messages and procedures of each specific
protocol.
TS 62351-5 © IEC:2009(E) – 9 –
Such documents shall not override any of the security measures described in this specifica-
tion as mandatory and normative.
When applied to IEC 60870-5-104, this specification shall be applied in conjunction with
IEC/TS 62351-3: Power systems management and associated information exchange – Data
and communications security – Part 3: Communication network and system security – Profiles
including TCP/IP.
1.5 Document organization and approach
This document is organized working from the general to the specific, as follows.
• Clauses 2 through 4 provide background terms, definitions, and references.
• Clause 5 describes the problems this specification is intended to address.
• Clause 6 describes the mechanism generically without reference to a specific protocol.
• Clauses 7 and 8 describe the mechanism more precisely and are the primary normative
part of this specification.
• Clause 9 describes a few particular implementation issues that are special cases.
• Clause 10 describes the requirements for other standards referencing this specification
• Clause 11 describes the protocol implementation conformance statement (PICS) for this
mechanism.
1.6 Compliance
Unless specifically labelled as informative or optional, all clauses of this specification are
normative.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60870-5-101, Telecontrol equipment and systems – Part 5-101: Transmission protocols –
Companion standard for basic telecontrol tasks
IEC 60870-5-102, Telecontrol equipment and systems – Part 5: Transmission protocols –
Section 102: Companion standard for the transmission of integrated totals in electric power
systems
IEC 60870-5-103, Telecontrol equipment and systems – Part 5-103: Transmission protocols -
Companion standard for the informative interface of protection equipment
IEC 60870-5-104, Telecontrol equipment and systems – Part 5-104: Transmission protocols –
Network access for IEC 60870-5-101 using standard transport profiles
IEC/TS 62351-1, Power systems management and associated information exchange – Data
and communications security – Part 1: Communication network and system security –
Introduction to security issues
IEC/TS 62351-2, Power systems management and associated information exchange – Data
and communications security – Part 2: Glossary of terms

– 10 – TS 62351-5 © IEC:2009(E)
IEC/TS 62351-3, Power systems management and associated information exchange – Data
and communications security – Part 3: Communication network and system security – Profiles
including TCP/IP
ISO/IEC 9798-4, Information technology – Security techniques – Entity authentication – Part
4: Mechanisms using a cryptographic check function
FIPS 186-2, Digital Signature Standard (DSS)
FIPS 197, Advanced Encryption Standard (AES)

FIPS 198-1, The Keyed-Hash Message Authentication Code

RFC 2104, HMAC: Keyed-Hashing for Message Authentication
RFC 3174, Secure Hash Algorithm (SHA-1)
RFC 3394, Advanced Encryption Standard (AES) Key Wrap Algorithm
RFC 3629, UTF-8, a transformation format of ISO 10646
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
They are described here because they are specific to the IEC 60870-5 standards and may be
useful for reading this specification as an independent document.
Refer to IEC/TS 62351-2 for a list of applicable terms and definitions.
3.1
controlling station
the device or application that initiates most of the communications and issues commands
It is commonly called a “master” in some protocol specifications.
3.2
controlled station
the remote device that transmits data gathered in the field to the controlling station
It is commonly called the “outstation” or “slave” in some protocols.
3.3
control direction
data transmitted by the controlling station to the controlled station(s)
3.4
monitoring direction
data transmitted by the controlled station to the controlling stations
The following terms are described here because they are specific to this protocol:
3.5
challenger
station that issues authentication challenges

TS 62351-5 © IEC:2009(E) – 11 –
It may be either a controlled or controlling station.
3.6
responder
station that responds or reacts to authentication challenges
It may be either a controlled or controlling station.
4 Abbreviated terms
Refer to IEC/TS 62351-2 for a list of applicable abbreviated terms. The following term is
included here because it is specifically used in the affected protocols and used in the
discussion of this authentication mechanism.
ASDU Application Service Data Unit. The application layer message submitted to
lower layers for transmission.

5 Problem description
5.1 Overview of clause
This clause is informative only. It describes:
• the security threats that this specification is intended to address;
• the unique design problems in implementing authentication for IEC 60870-5 and derived
protocols;
• the resulting design principles behind the mechanism.
5.2 Specific threats addressed
This specification shall address only the following security threats, as defined in
IEC/TS 62351-2:
• spoofing;
• modification;
• replay;
• non-repudiation – to the extent of identifying individual users of the system.
5.3 Design issues
5.3.1 Overview of subclause
This subclause describes the challenges faced in developing an authentication proposal that
can be applied to all the IEC 60870-5 and derivative protocols. This subclause is supplied for
the benefit of security experts reviewing this document who may not be familiar with the
electrical utility protocol environment.
5.3.2 Asymmetric communications
All the protocols affected by this specification share the concept of inequality between the
communication stations. In each of these protocols, there is a designated controlling station
and a designated controlled station, each having different roles, responsibilities, procedures
and message formats. In particular, the controlling station is in many cases responsible for
flow control and media access control.

– 12 – TS 62351-5 © IEC:2009(E)
The existence of a definite controlled/controlling station designation has two impacts on the
design of this authentication mechanism:
• the format of messages in each direction will differ, even if the functions are the same;
• key distribution is simplified because they will always be issued by the controlling station.
5.3.3 Message-oriented
All of the affected protocols are message-oriented. This means that authentication must be
performed on a message-by-message basis, rather than authenticating only at the beginning
of a data stream and occasionally thereafter, as some connection-oriented protocols do.
5.3.4 Poor sequence numbers or no sequence numbers
A common security technique to address the threat of replay is to include in the message a
sequence number. Combined with tests for message integrity, the sequence number makes it
harder for an attacker to simulate a legitimate user by just copying an existing message,
because the messages must be transmitted in a particular order.
Unfortunately, none of the affected protocols includes a sequence number that would provide
adequate protection. Those sequence numbers that do exist have very low maximum values,
permitting an attacker to attempt a replay after gathering only a small number of messages.
Therefore, the design of this specification must include its own sequence numbers and other
time-varying data to protect against replay.
5.3.5 Limited processing power
The lack of processing power available on many power utility devices has been a major
design concern for the affected protocols since their creation. This design requirement
necessarily affects the authentication mechanism also. The concern is heightened by the fact
that many of these devices are single-processor machines; a denial-of-service attack would
affect not only the communications capability of such devices but their function as an
electrical control, protection, or monitoring device also.
Therefore, the use of security measures requiring extremely high processing power, such as
public-key encryption and very large key sizes, has been avoided as much as possible.
5.3.6 Limited bandwidth
The limited amount of bandwidth available in utility networks has been the prime design
concern (after message integrity) of the affected protocols. Links of 1 200 bits per second and
lower are still a reality for many applications of these protocols. Some communications links
also charge costs per octet transmitted.
Therefore, the authentication mechanism must not add very much overhead (i.e. few octets)
to the affected protocols. The size of the challenge and authentication data has therefore
been limited and truncated as much as possible while retaining an adequate level of security.
Other measures may be taken in the implementations in each protocol.
5.3.7 No access to authentication server
The nature of the utility networks in which the affected protocols are deployed is that the
controlling station is often the only device with which the controlled station can communicate.
If there is any access to other networks, it is often achieved through the device implementing
the controlling station.
The impact of this fact on the authentication mechanism is that any system requiring on-line
verification of the controlling station’s security credentials by a third party is not practical.

TS 62351-5 © IEC:2009(E) – 13 –
5.3.8 Limited frame length
Because of the restrictions on bandwidth and message integrity, the affected protocols are
designed to send data in small frames of 255 octets or less. Some derivative protocols permit
“chaining” frames together to create larger application layer messages.
However, in general, the authentication mechanism cannot assume the transmission of large
data units between the stations.
5.3.9 Limited checksum
Message integrity was a high priority in the design of the affected protocols. However, the
integrity measures chosen for these protocols were designed to protect against random noise,
and not a concerted attack, as discussed below.
• The serial IEC 60870-5 protocols use frame type FT1.2, which uses parity bits and a
single-octet checksum to protect against bit errors. A single octet is not large enough to
provide a secure message authentication code (MAC).
• The IEC 60870-5-104 protocol depends on the integrity measures of lower layers.
Because this specification discusses an application layer mechanism only, it cannot
depend on such measures. In any case, doing so would provide a solution for only one of
the affected protocols.
• The DNP3 protocol uses the IEC 60870-5 FT3 frame, with a two-octet cyclic redundancy
check every 16 octets or fewer. This provides considerable integrity for security purposes,
except that there is no check for the entire frame.
Therefore, the authentication mechanism described in this specification cannot make use of
the existing protocol integrity mechanisms to provide message integrity for security purposes.
5.3.10 Radio systems
The affected protocols are often used over radio systems which may or may not provide
security measures of their own. Many existing utility radio networks provide no security at all.
Therefore, the mechanism described in this specification must assume a hostile and
physically insecure transmission environment.
5.3.11 Dial-up systems
The affected protocols are often used over dial-up telephone networks which require several
seconds to re-establish communications before each frame transmitted. Similarly, many radio
systems require long “keying” times before each frame.
Therefore, the authentication mechanism provides an option, known as “aggressive mode”
that reduces the number of extra frames of data to be transmitted.
5.3.12 Variety of protocols affected
The IEC 60870-5 family of protocols share many common functions and an underlying design
philosophy. However, the various companion standards and derivative protocols have been
implemented using a variety of message formats and procedures.
Therefore, this specification describes a generic authentication mechanism that must be
mapped to each specific affected protocol within specifications that are specific to that
protocol.
– 14 – TS 62351-5 © IEC:2009(E)
5.3.13 Differing data link layers
As discussed in 5.3.9, the affected protocols use a variety of transport mechanisms and
procedures. Although IEC 60870-5 describes a common data link layer, it permits multiple
frame formats and other options. Several of the affected protocols use the FT1.2 frame, one
uses FT3, and one does not use that frame format at all. Some of them use only an
unbalanced media access control procedure, some use a balanced method, and some
optionally use both.
Therefore, the authentication mechanism cannot be based on the data link layer. However, it
can assume that there is addressing information available from lower layers that can be used
for authentication.
5.3.14 Long upgrade intervals
Utilities depreciate changes to their networks over long periods, and may deploy several
different generations of network systems simultaneously.
Therefore, this authentication mechanism follows the principles described in 5.4.8.
5.3.15 Remote sites
The devices that implement the affected protocols are often located at sites that are very
remote and expensive to access.
Therefore, as much as possible, this mechanism includes methods of updating security cred-
entials remotely.
5.3.16 Multiple users
A common topology for the affected protocols is for multiple users (such as control consoles,
or operators) to access the controlled station through a single controlling station. For non-
repudiation purposes, it is important to know which of these users sent a particular command
of the controlled station.
Therefore, this mechanism includes methods to authenticate individual users separately from
the controlling station itself.
5.3.17 Unreliable media
The affected protocols are often used over unreliable media. This mechanism attempts to take
this unreliability into account when addressing error conditions. For instance, it does not
assume that the loss of a single security message necessarily means that an attack is under-
way.
5.4 General principles
5.4.1 Overview of subclause
This subclause describes the guiding principles behind this specification, based on the
identified threats and design issues discussed in the previous two clauses.
5.4.2 Authentication only
As discussed in Clause 1, this specification addresses authentication only, not encryption or
other security measures. It does not rule out the possibility of such measures being added to
the affected protocols by other standards.

TS 62351-5 © IEC:2009(E) – 15 –
5.4.3 Application layer only
This specification describes authentication at the application layer. Refer to IEC/TS 62351-1
for a discussion of why application layer authentication is necessary in the utility environment,
in addition to any transport layer security that may be implemented.
5.4.4 Generic definition mapped onto different protocols
This specification describes a common method of authentication that can be used by any of
the affected protocols. The implementation of this method in each protocol shall be defined by
separate standards. Such standards shall reference this specification according to the rules
defined in Clause 10.
5.4.5 Bi-directional
This specification describes a mechanism that can be used in either transmission direction,
despite the asymmetry of communications traffic defined by the affected protocols and dis-
cussed in 5.3.2.
5.4.6 Challenge-response
The mechanism described in this specification is based on the concept of challenge and reply.
This principle has been applied for the following reasons.
• It places the responsibility for security on the device that requires authentication, which is
more practical in a diverse network such as those found in the utility industry.
• It permits some communication to be left unsecured if desired, reducing bandwidth and
processing requirements.
• It works effectively in a non-connection-oriented environment.
Because “response” is a keyword in the affected protocols, the term used in this specification
is “reply”.
5.4.7 Pre-shared keys a
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