ISO/IEC 11770-4:2017

INTERNATIONAL ISO/IEC
STANDARD 11770-4
Second edition
2017-11
Information technology — Security
techniques — Key management —
Part 4:
Mechanisms based on weak secrets
Technologies de l'information — Techniques de sécurité — Gestion
de clés —
Partie 4: Mécanismes basés sur des secrets faibles
Reference number
©
ISO/IEC 2017
© ISO/IEC 2017, Published in Switzerland
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ii © ISO/IEC 2017 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative reference . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 6
5 Requirements . 8
6 Password-authenticated key agreement .10
6.1 General .10
6.2 Balanced Key Agreement Mechanism 1 (BKAM1) .10
6.2.1 General.10
6.2.2 Prior shared parameters .11
6.2.3 Functions .11
6.2.4 Key agreement operation .14
6.3 Balanced Key Agreement Mechanism 2 (BKAM2) .15
6.3.1 General.15
6.3.2 Prior shared parameters .15
6.3.3 Functions .16
6.3.4 Key agreement operation .19
6.4 Augmented Key Agreement Mechanism 1 (AKAM1) .22
6.4.1 General.22
6.4.2 Prior shared parameters .22
6.4.3 Functions .23
6.4.4 Key agreement operation .24
6.5 Augmented Key Agreement Mechanism 2 (AKAM2) .25
6.5.1 General.25
6.5.2 Prior shared parameters .26
6.5.3 Functions .26
6.5.4 Key agreement operation .29
6.6 Augmented Key Agreement Mechanism 3 (AKAM3) .30
6.6.1 General.30
6.6.2 Prior shared parameters .30
6.6.3 Functions .31
6.6.4 Key agreement operation .33
7 Password-authenticated key retrieval .35
7.1 General .35
7.2 Key Retrieval Mechanism 1 (KRM1).35
7.2.1 General.35
7.2.2 Prior shared parameters .36
7.2.3 Functions .36
7.2.4 Key retrieval operation . .37
Annex A (normative) Functions for data type conversion .38
Annex B (normative) Object identifiers .42
Annex C (informative) Guidance on choice of parameters .45
Bibliography .47
© ISO/IEC 2017 – 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. In the field of information technology, ISO and IEC have established a joint technical committee,
ISO/IEC JTC 1.
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 ISO documents 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 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).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by ISO/IEC JTC 1, Information technology, SC 27, IT Security techniques.
This second edition cancels and replaces the first edition (ISO/IEC 11770-4:2006), which has been
technically revised. It also incorporates the Technical Corrigendum ISO/IEC 11770-4:2006/Cor1:2009.
This edition includes the following significant changes with respect to the previous edition:
— revision of the Balanced Key Agreement Mechanism 1 (BKAM1) to address the attacks reported in
Reference [6];
— addition of a new Balanced Key Agreement Mechanism 2 (BKAM2) based on the J-PAKE scheme of
Reference [5];
— addition of a new Augmented Key Agreement Mechanism 3 (AKAM3) based on the AugPAKE scheme
of Reference [23].
A list of all parts in the ISO/IEC 11770 series can be found on the ISO website.
iv © ISO/IEC 2017 – All rights reserved

Introduction
The mechanisms specified in this document are designed to achieve one of the following three goals.
a) Balanced password-authenticated key agreement: Establish one or more shared secret keys
between two entities that share a common weak secret. In a balanced password-authenticated key
agreement mechanism, the shared secret keys are the result of a data exchange between the two
entities; the shared secret keys are established if, and only if, the two entities have used the same
weak secret; and neither of the two entities can predetermine the values of the shared secret keys.
b) Augmented password-authenticated key agreement: Establish one or more shared secret keys
between two entities A and B, where A has a weak secret and B has verification data derived from
a one-way function of A’s weak secret. In an augmented password-authenticated key agreement
mechanism, the shared secret keys are the result of a data exchange between the two entities; the
shared secret keys are established if, and only if, the two entities have used the weak secret and the
corresponding verification data; and neither of the two entities can predetermine the values of the
shared secret keys.
NOTE 1 This type of key agreement mechanism is unable to protect A’s weak secret being discovered by
B, but only increases the cost for an adversary to get A's weak secret from B. A typical application scenario
would involve use between a client (A) and a server (B).
c) Password-authenticated key retrieval: Establish one or more secret keys for an entity, A,
associated with another entity, B, where A has a weak secret and B has a strong secret associated
with A's weak secret. In an authenticated key retrieval mechanism, the secret keys, retrievable by
A (not necessarily derivable by B), are the result of a data exchange between the two entities, and
the secret keys are established if, and only if, the two entities have used the weak secret and the
associated strong secret. However, although B’s strong secret is associated with A's weak secret,
the strong secret does not (in itself) contain sufficient information to permit either the weak secret
or the secret keys established in the mechanism to be determined.
NOTE 2 This type of key retrieval mechanism is used in those applications where A does not have secure
storage for a strong secret, and requires B’s assistance to retrieve the strong secret. Such a mechanism is
appropriate for use
...