Overview
ISO/IEC 20009-4:2017 defines privacy-preserving, anonymous entity authentication mechanisms that are based on weak secrets (for example, passwords). Part 4 of the ISO/IEC 20009 series specifies the precise operation, inputs and outputs of each mechanism so that a server can verify that a user belongs to a given user group without obtaining identifying information that could be used later to trace the user. The standard supports password-based anonymous entity authentication (PAEA) and addresses the special considerations when using weak secrets for privacy-preserving authentication.
Key topics
- Scope and objectives
- Anonymous entity authentication using weak secrets (passwords).
- Server verifies group membership while preserving user anonymity.
- PAEA mechanism types
- Password-only PAEA mechanisms - users register password verification data at the server and remember only the password.
- Storage-extra PAEA mechanisms - users hold additional password-wrapped credentials (revealable without breaking privacy); server does not retain password verification data.
- Mechanisms specified
- Named mechanisms in the document include SKI, YZ, and YZW (storage-extra).
- Each mechanism is defined with setup, user registration, anonymous authentication, and user revocation procedures.
- Technical building blocks
- Symbols, conversion functions, and terminology for cryptographic groups, hash- and MAC-functions, authenticated encryption, and credentials.
- Attention to attacks on weak secrets, exhaustive search considerations, and revocation handling.
- Outputs and identifiers
- Details of inputs/outputs for each protocol step; Annex A provides object identifiers for the mechanisms.
- Patent and compliance notes
- The standard notes potential patent claims (e.g., patent declarations provided by an identified organization) and references ISO/IEC patent resources.
Applications
- Privacy-preserving access control for services that need to verify membership of a group (e.g., subscriber-only resources, forums, event access) without collecting persistent identity data.
- Anonymous authentication in federated or decentralized systems where user traceability must be minimized.
- Systems constrained to passwords/weak secrets where hardware tokens are impractical but privacy goals remain important.
- Typical users:
- Security architects and protocol designers implementing anonymous authentication.
- Developers of identity and access management (IAM) systems, privacy engineers, and compliance teams.
Related standards
Keywords: ISO/IEC 20009-4:2017, anonymous entity authentication, weak secrets, password-based anonymous authentication (PAEA), privacy-preserving authentication, SKI, YZ, YZW.