ISO/IEC 11770-5:2020
(Main)Information security — Key management — Part 5: Group key management
Information security — Key management — Part 5: Group key management
This document specifies mechanisms to establish shared symmetric keys between groups of entities. It defines: — symmetric key-based key establishment mechanisms for multiple entities with a key distribution centre (KDC); and — symmetric key establishment mechanisms based on a general tree-based logical key structure with both individual rekeying and batch rekeying. It also defines key establishment mechanisms based on a key chain with group forward secrecy, group backward secrecy or both group forward and backward secrecy. This document also describes the required content of messages which carry keying material or are necessary to set up the conditions under which the keying material can be established. This document does not specify information that has no relation with key establishment mechanisms, nor does it specify other messages such as error messages. The explicit format of messages is not within the scope of this document. This document does not specify the means to be used to establish the initial secret keys required to be shared between each entity and the KDC, nor key lifecycle management. This document also does not explicitly address the issue of interdomain key management.
Sécurité de l'information — Gestion de clés — Partie 5: Gestion de clés de groupe
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INTERNATIONAL ISO/IEC
STANDARD 11770-5
Second edition
2020-11
Information security — Key
management —
Part 5:
Group key management
Sécurité de l'information — Gestion de clés —
Partie 5: Gestion de clés de groupe
Reference number
©
ISO/IEC 2020
© ISO/IEC 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2020 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 4
5 Requirements . 5
6 Tree-based key establishment mechanisms . 5
6.1 General model . 5
6.2 Joining process . 6
6.3 Leaving process . 6
6.4 Rekeying process . 6
6.5 Logical key structure. 6
6.5.1 General. 6
6.5.2 Star-based structure . 6
6.5.3 d-ary tree-based structure . 7
6.5.4 General tree-based structure . 7
6.6 Symmetric key-based key establishment mechanisms . 8
6.6.1 General. 8
6.6.2 Mechanism 1 — Key establishment mechanism with individual rekeying . 8
6.6.3 Mechanism 2 — Key establishment mechanism with batch rekeying .10
7 Key chain-based group key management with limited forward key chain .12
7.1 General model .12
7.2 Calculations by the key distribution centre .13
7.2.1 Key chains .13
7.2.2 Group forward secrecy .13
7.2.3 Group backward secrecy .14
7.2.4 Forward and backward secrecy .14
7.3 Calculations by the client entity .15
Annex A (normative) Object identifiers .16
Annex B (informative) Load-balancing mechanism for a general tree-based structure .17
Bibliography .18
© ISO/IEC 2020 – All rights reserved iii
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that
are members of ISO or IEC participate in the development of International Standards through
technical committees established by the respective organization to deal with particular fields of
technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other
international organizations, governmental and non-governmental, in liaison with ISO and IEC, also
take part in the work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the IEC
list of patent declarations received (see http:// patents .iec .ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 27, Information security, cybersecurity and privacy protection.
This second edition cancels and replaces the first edition (ISO/IEC 11770-5:2011) which has been
technically revised.
The main changes compared to the previous edition are as follows:
— the document has been modified to be consistent with use of the key deriviation specifications from
ISO/IEC 11770-6;
— the use of a "trapdoor" in key derivation has been removed. Consequently, unlimited forward key
chains can no longer be calculated.
A list of all parts in the ISO/IEC 11770 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO/IEC 2020 – All rights reserved
Introduction
In some applications, it is necessary for a secret cryptographic key to be shared by a group of entities.
Moreover, in some cases the exact membership of a group of entities that share a key may change
over time.
This document is concerned with techniques that enable a secret key to be shared by all members
of a defined group with the assistance of a trusted third party known as a key distribution centre.
Provisions for adding and removing members of a group are also made.
© ISO/IEC 2020 – All rights reserved v
INTERNATIONAL STANDARD ISO/IEC 11770-5:2020(E)
Information security — Key management —
Part 5:
Group key management
1 Scope
This document specifies mechanisms to establish shared symmetric keys between groups of entities. It
defines:
— symmetric key-based key establishment mechanisms for multiple entities with a key distribution
centre (KDC); and
— symmetric key establishment mechanisms based on a general tree-based logical key structure with
both individual rekeying and batch rekeying.
It also defines key establishment mechanisms based on a key chain with group forward secrecy, group
backward secrecy or both group forward and backward secrecy.
This document also describes the required content of messages which carry keying material or are
necessary to set up the conditions under which the keying material can be established.
This document does not specify information that has no relation with key establishment mechanisms,
nor does it specify other messages such as error messages. The explicit format of messages is not within
the scope of this document.
This document does not specify the means to be used to establish the initial secret keys required to be
shared between each entity and the KDC, nor key lifecycle management. This document also does not
explicitly address the issue of interdomain key management.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
ISO/IEC 19772, Information technology — Security techniques — Authenticated encryption
ISO/IEC 11770-6, Information technology — Security techniques — Key management — Part 6: Key
derivation
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
active
state of an entity in which the entity can obtain the shared secret key (3.24)
© ISO/IEC 2020 – All rights reserved 1
3.2
ancestor key
ancestor key of an entity x
cryptographic key in a logical key hierarchy (3.17) that is assigned to a node on the direct path from the
leaf node (3.16) corresponding to the individual key (3.11) for x and the root node (3.23)
Note 1 to entry: An ancestor key is either the shared secret key or a key encryption key.
3.3
backward secrecy with interval T
security condition in which an entity joining a set of entities at time t = t cannot obtain any secret keys
established between these entities at any time prior to t – T
3.4
batch rekeying with interval T
rekeying method in which the shared secret key (3.24) and, optionally, key encryption keys (3.15) are
updated at every time interval T (see Clause 4)
3.5
child key
child key for a node w
cryptographic key in a logical key hierarchy (3.17) assigned to a non-root node w
Note 1 to entry: A child key shall be a key encryption key or individual key.
3.6
child node
child node of a node w
node in a tree (3.25) that is adjacent to w and for which w lies on the unique path between it and the root
node (3.23)
3.7
d-ary tree
tree (3.25) where each node has d child nodes (3.6) except the leaf nodes (3.16) in the tree
3.8
forward secrecy with interval T
security condition in which an entity leaving a set of entities at time t = t cannot obtain any secret keys
established between these entities at any time subsequent to t + T
3.9
group backward secrecy
security condition in which an entity joining a set of entities cannot obtain any secret keys previously
established between these entities
3.10
group forward secrecy
security condition in which an entity leaving a set of entities cannot obtain any secret keys subsequently
established between these entities
3.11
individual key
key shared between the key distribution centre (3.14) and each entity
3.12
individual rekeying
rekeying method in whic
...
INTERNATIONAL ISO/IEC
STANDARD 11770-5
Second edition
2020-11
Information security — Key
management —
Part 5:
Group key management
Sécurité de l'information — Gestion de clés —
Partie 5: Gestion de clés de groupe
Reference number
©
ISO/IEC 2020
© ISO/IEC 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2020 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 4
5 Requirements . 5
6 Tree-based key establishment mechanisms . 5
6.1 General model . 5
6.2 Joining process . 6
6.3 Leaving process . 6
6.4 Rekeying process . 6
6.5 Logical key structure. 6
6.5.1 General. 6
6.5.2 Star-based structure . 6
6.5.3 d-ary tree-based structure . 7
6.5.4 General tree-based structure . 7
6.6 Symmetric key-based key establishment mechanisms . 8
6.6.1 General. 8
6.6.2 Mechanism 1 — Key establishment mechanism with individual rekeying . 8
6.6.3 Mechanism 2 — Key establishment mechanism with batch rekeying .10
7 Key chain-based group key management with limited forward key chain .12
7.1 General model .12
7.2 Calculations by the key distribution centre .13
7.2.1 Key chains .13
7.2.2 Group forward secrecy .13
7.2.3 Group backward secrecy .14
7.2.4 Forward and backward secrecy .14
7.3 Calculations by the client entity .15
Annex A (normative) Object identifiers .16
Annex B (informative) Load-balancing mechanism for a general tree-based structure .17
Bibliography .18
© ISO/IEC 2020 – All rights reserved iii
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that
are members of ISO or IEC participate in the development of International Standards through
technical committees established by the respective organization to deal with particular fields of
technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other
international organizations, governmental and non-governmental, in liaison with ISO and IEC, also
take part in the work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the IEC
list of patent declarations received (see http:// patents .iec .ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 27, Information security, cybersecurity and privacy protection.
This second edition cancels and replaces the first edition (ISO/IEC 11770-5:2011) which has been
technically revised.
The main changes compared to the previous edition are as follows:
— the document has been modified to be consistent with use of the key deriviation specifications from
ISO/IEC 11770-6;
— the use of a "trapdoor" in key derivation has been removed. Consequently, unlimited forward key
chains can no longer be calculated.
A list of all parts in the ISO/IEC 11770 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO/IEC 2020 – All rights reserved
Introduction
In some applications, it is necessary for a secret cryptographic key to be shared by a group of entities.
Moreover, in some cases the exact membership of a group of entities that share a key may change
over time.
This document is concerned with techniques that enable a secret key to be shared by all members
of a defined group with the assistance of a trusted third party known as a key distribution centre.
Provisions for adding and removing members of a group are also made.
© ISO/IEC 2020 – All rights reserved v
INTERNATIONAL STANDARD ISO/IEC 11770-5:2020(E)
Information security — Key management —
Part 5:
Group key management
1 Scope
This document specifies mechanisms to establish shared symmetric keys between groups of entities. It
defines:
— symmetric key-based key establishment mechanisms for multiple entities with a key distribution
centre (KDC); and
— symmetric key establishment mechanisms based on a general tree-based logical key structure with
both individual rekeying and batch rekeying.
It also defines key establishment mechanisms based on a key chain with group forward secrecy, group
backward secrecy or both group forward and backward secrecy.
This document also describes the required content of messages which carry keying material or are
necessary to set up the conditions under which the keying material can be established.
This document does not specify information that has no relation with key establishment mechanisms,
nor does it specify other messages such as error messages. The explicit format of messages is not within
the scope of this document.
This document does not specify the means to be used to establish the initial secret keys required to be
shared between each entity and the KDC, nor key lifecycle management. This document also does not
explicitly address the issue of interdomain key management.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
ISO/IEC 19772, Information technology — Security techniques — Authenticated encryption
ISO/IEC 11770-6, Information technology — Security techniques — Key management — Part 6: Key
derivation
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
active
state of an entity in which the entity can obtain the shared secret key (3.24)
© ISO/IEC 2020 – All rights reserved 1
3.2
ancestor key
ancestor key of an entity x
cryptographic key in a logical key hierarchy (3.17) that is assigned to a node on the direct path from the
leaf node (3.16) corresponding to the individual key (3.11) for x and the root node (3.23)
Note 1 to entry: An ancestor key is either the shared secret key or a key encryption key.
3.3
backward secrecy with interval T
security condition in which an entity joining a set of entities at time t = t cannot obtain any secret keys
established between these entities at any time prior to t – T
3.4
batch rekeying with interval T
rekeying method in which the shared secret key (3.24) and, optionally, key encryption keys (3.15) are
updated at every time interval T (see Clause 4)
3.5
child key
child key for a node w
cryptographic key in a logical key hierarchy (3.17) assigned to a non-root node w
Note 1 to entry: A child key shall be a key encryption key or individual key.
3.6
child node
child node of a node w
node in a tree (3.25) that is adjacent to w and for which w lies on the unique path between it and the root
node (3.23)
3.7
d-ary tree
tree (3.25) where each node has d child nodes (3.6) except the leaf nodes (3.16) in the tree
3.8
forward secrecy with interval T
security condition in which an entity leaving a set of entities at time t = t cannot obtain any secret keys
established between these entities at any time subsequent to t + T
3.9
group backward secrecy
security condition in which an entity joining a set of entities cannot obtain any secret keys previously
established between these entities
3.10
group forward secrecy
security condition in which an entity leaving a set of entities cannot obtain any secret keys subsequently
established between these entities
3.11
individual key
key shared between the key distribution centre (3.14) and each entity
3.12
individual rekeying
rekeying method in whic
...
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