ISO/IEC 20009-4:2017/Amd 1:2026

International
Standard
ISO/IEC 20009-4
First edition
Information technology — Security
2017-08
techniques — Anonymous entity
authentication —
AMENDMENT 1
2026-10
Part 4:
Mechanisms based on weak secrets
AMENDMENT 1
Technologies de l'information — Techniques de sécurité —
Authentification d'entité anonyme —
Partie 4: Mécanismes basés sur des secrets faibles
AMENDEMENT 1
Reference number
ISO/IEC 20009-4:2017/Amd. 1:2026(en) © ISO/IEC 2026

ISO/IEC 20009-4:2017/Amd. 1:2026(en)
© ISO/IEC 2026
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© ISO/IEC 2026 – All rights reserved
ii
ISO/IEC 20009-4:2017/Amd. 1:2026(en)
Foreword
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© ISO/IEC 2026 – All rights reserved
iii
ISO/IEC 20009-4:2017/Amd. 1:2026(en)
Information technology — Security techniques — Anonymous
entity authentication —
Part 4:
Mechanisms based on weak secrets
AMENDMENT 1
Clause 2
Add the following normative references:
ISO/IEC 14888-2, Information technology — Security techniques — Digital signatures with appendix —
Part 2: Integer factorization based mechanisms
ISO/IEC 14888-3, IT Security techniques — Digital signatures with appendix — Part 3: Discrete logarithm
based mechanisms
ISO/IEC 18033-2, Information technology — Security techniques — Encryption algorithms — Part 2:
Asymmetric ciphers
4.2
Replace the text in this subclause as follows:
EC2OSP elliptic curve point to octet string conversion primitive, which shall be equivalent to
the specified conversion primitive EC2OSP (P, compressed) for a point P over an elliptic
E
curve E in accordance with ISO/IEC 18033-2
FE2OSP field element to octet string conversion primitive, which shall be as specified in ISO/IEC
18033-2
BS2IP bit string to integer conversion primitive, which shall be as specified in ISO/IEC 18033-2
GE2OSP cyclic group element to octet string conversion primitive. If the mechanism is defined
over a finite field, it is the same as FE2OSP. If it is defined over an elliptic curve, it is the
same as EC2OSP.
5.3
Replace the paragraph beginning with “Setup” as follows:
Setup: Given a security parameter secparam, the server generates and maintains a tuple
params,PWF  , where params denotes public system parameters and PWF is a password file,
initially set empty, that is kept private. The password file PWF consists of a set of ordered pairs,
Ip, vd , one for each member of the user group, where I and pvd are the distinguishing identifier
U U
UU
and password verification data for the user, U, respectively. params will be the common input to the

© ISO/IEC 2026 – All rights reserved
ISO/IEC 20009-4:2017/Amd. 1:2026(en)
other operations of the mechanism, but for simplicity, it is deliberately omitted from the specifications
of inputs of the operations.
Replace the paragraph beginning with “User registration” as follows:
User registration: This process can be non-interactive if PWF is empty. Otherwise, it should be
interactive to avoid registering duplicate identifiers. Given a user's distinguishing identifier, I , and a
U
password, pw , from the user and a password file, PWF, from the server, generate password verification
U
data, pvd , and then add Ip, vd to the password file, PWF.
U
UU
Replace the paragraph beginning with “User revocation” as follows:
User revocation: Given a user identity, I , and a password file, PWF, the server removes Ip, vd
U
UU
from the password file, PWF, and then update the pre-computed values, if any.
Remove the paragraph beginning with “NOTE 1”.
Replace the paragraph beginning with “NOTE 2” as follows:
NOTE The anonymous authentication operation is specified to include mutual authentication and key
exchange. Depending on the application, it can be minimally specified to include only unilateral authenti-
cation from a user to a server or a server authenticates only that the user belongs to a certain user group,
without the opposite direction of authentication and key exchange.

5.4
Replace the paragraph beginning with “User registration” as follows:
User registration: This is an interactive process between a user and a server. Given a user's
distinguishing identifier, I , and a password, pw , from the user and the server key, ServK, from the
U U
server, output a password wrapped credential, cred . cred may be stored anywhere accessible to
pw pw
U U
the user, e.g. in a portable storage device or a public directory.
Replace the paragraph beginning with “User revocation” as follows:
User revocation: Given a user's distinguishing identifier, I , and password wrapped credential,
U
cred , the server revokes the authentication credential for I and updates CRL (Credential Revocation
U
pw
U
List) such that CRL = CRL ∪ {cred}, where CRL is the updated CRL and CRL is the old CRL and
new old new old
cred is the original credential contained in cred . CRL is part of params and is initially set empty. The
pw
U
server maintains CRL, and the details depend on each mechanism in 7.
Remove NOTE 1.
Replace NOTE 2 as follows:
NOTE The anonymous authentication operation is specified to include mutual authentication and key
exchange. Depending on the application, it can be minimally specified to include only unilateral authenti-
cation from a user to a server or a server authenticates only that the user belongs to a certain user group,
without authentication from a server to a user and key exchange.

6.2.2
Replace bullet point c) with the following text:

© ISO/IEC 2026 – All rights reserved
ISO/IEC 20009-4:2017/Amd. 1:2026(en)
c) U is added to a legitimate user group where the user group is denoted by U.
i
6.2.4
Replace the text as follows:
The SKI mechanism supports two types of user revocation: 1) exclude the user only from some user
groups while leaving the user in the other user groups and in the password file, PWF, 2) exclude the user
from the password file, PWF. In the former case, execute only step b) below and in the latter case execute
both a) and b). A user U can be revoked by the server, S, as follows.
i
a) Remove Ip, vd from the
...