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BS ISO IEC 20009 — Anonymous Entity Authentication Standard Series
Information technology — Security techniques — Anonymous entity authentication — Part 1 & Part 2
🪪 BS ISO/IEC 20009 is the British Standards Institution (BSI) adoption of the ISO/IEC 20009 series, covering anonymous entity authentication as an information-security technique. Unlike ordinary entity authentication, anonymous entity authentication lets an entity prove its legitimacy to a verifier without revealing its identity; it is common in privacy-preserving scenarios such as vehicle anonymous credentials, access control, and electronic voting. It was prepared by UK technical committee IST/33 (IT — Security techniques) and carries ICS classification 35.040. The series currently comprises two parts: Part 1 specifies the general requirements and Part 2 specifies mechanisms based on signatures using a group public key.
💡 The goal of anonymous entity authentication is to “prove that I am a legitimate member of the group, but not to say who I am” — especially valuable in scenarios where the service provider does not need to know the individual identity but only to confirm authorisation.
1. Series Overview and Positioning 📌
Entity authentication confirms that an entity really holds a certain identity. Anonymous entity authentication adds anonymity on top: the verifier can be certain the entity belongs to a group but cannot identify its specific identity. The ISO/IEC 20009 series provides a unified model, requirements, and mechanisms for this kind of authentication.
The two parts currently in the BS ISO/IEC 20009 series are shown below. Part 1 establishes the anonymous entity authentication model and general requirements, and Part 2 gives concrete mechanisms based on signatures using a group public key.
| Standard | Subject | Key Content | Edition |
|---|---|---|---|
| BS ISO/IEC 20009-1:2013 | General | Anonymous entity authentication model, general requirements, and constraints | First edition 2013-08-01 |
| BS ISO/IEC 20009-2:2013 | Mechanisms based on signatures using a group public key | Anonymous entity authentication mechanisms based on group-public-key signatures, key generation, and protocol | First edition 2013-12-01 |
⚠️ Anonymous entity authentication is closely related to anonymous digital signatures but focuses differently: anonymous signatures emphasise “anonymity of the signature”, while anonymous entity authentication emphasises “anonymous proof of entity identity” — the latter is usually built on anonymous signatures as a primitive.
2. Anonymous Entity Authentication Model and Requirements 🏗️
BS ISO/IEC 20009-1 defines the anonymous entity authentication model, clarifying the participating entities (such as claimant, verifier, and authorisation authority), the protocol interaction, and the security objectives. The general requirements and constraints specified by the Standard include:
- Anonymity: the verifier cannot identify the specific entity identity.
- Verifiability: the verifier can confirm the entity belongs to the authorised group.
- Anti-replay and anti-forgery: prevent an attacker from intercepting and replaying authentication messages or forging identity.
- Revocability (optional): the authorisation authority may reveal the entity identity under specific conditions.
3. Mechanisms Based on Group-Public-Key Signatures 🔧
BS ISO/IEC 20009-2 specifies anonymous entity authentication mechanisms based on signatures using a group public key. A group-public-key signature lets an entity generate a verifiable signature with a member key, while the verifier only needs the group public key to confirm membership, maintaining anonymity. The Standard specifies:
- Key generation process: the generation flow for the group public key and member keys.
- Authentication protocol: the challenge-response flow by which an entity proves membership to a verifier.
- Security properties: anonymity, unforgeability, revocability, etc.
💡 The advantage of the group-public-key signature mechanism in anonymous entity authentication is “one authorisation, many anonymous authentications”: an entity proves its identity to the authority once to obtain a member key, then can anonymously pass verification many times without re-exposing its identity.
4. Engineering Practice and Applications 🔍
Anonymous entity authentication is widely used in privacy-preserving identity verification. Engineering practice points include:
- Vehicle anonymous credentials: in vehicle-to-everything (V2X), a vehicle proves its legitimate identity to roadside units with anonymous credentials, protecting the owner’s privacy.
- Access control: “eligibility-only” access that does not identify the individual, such as membership venues and anonymous reporting channels.
- Electronic voting: a voter anonymously proves voting eligibility before voting, achieving one-person-one-vote while protecting anonymity.
- Authority management: clearly define the key escrow and revocation authority of the issuing authority, balancing anonymity with accountability needs.
5. Frequently Asked Questions ❓
❓ Q: How does anonymous entity authentication differ from ordinary entity authentication?
A: Ordinary authentication verifies “you are you” and requires identifying the specific identity; anonymous authentication verifies “you are a legitimate group member” without exposing identity, suited to scenarios requiring only proof of eligibility.
A: Ordinary authentication verifies “you are you” and requires identifying the specific identity; anonymous authentication verifies “you are a legitimate group member” without exposing identity, suited to scenarios requiring only proof of eligibility.
❓ Q: Why is Part 2 based on “group-public-key signatures”?
A: Group-public-key signatures are naturally suited to anonymous membership proof: a member signs with its private key, and the verifier confirms membership with the group public key, without being able to determine the specific member.
A: Group-public-key signatures are naturally suited to anonymous membership proof: a member signs with its private key, and the verifier confirms membership with the group public key, without being able to determine the specific member.
❓ Q: Is anonymous entity authentication fully anonymous?
A: It depends on whether revocation is enabled. Many mechanisms allow the authorisation authority to reveal identity under specific conditions, so anonymity is usually “conditional” rather than absolute.
A: It depends on whether revocation is enabled. Many mechanisms allow the authorisation authority to reveal identity under specific conditions, so anonymity is usually “conditional” rather than absolute.
🔍 Q: What is the value of anonymous entity authentication in V2X?
A: It lets a vehicle prove its legitimate identity to roadside units without exposing owner information, satisfying both secure message authentication and personal privacy — an important security building block of V2X.
A: It lets a vehicle prove its legitimate identity to roadside units without exposing owner information, satisfying both secure message authentication and personal privacy — an important security building block of V2X.