| Internet-Draft | reclaimid | April 2024 |
| Schanzenbach & Grothoff | Expires 10 October 2024 | [Page] |
This document contains the re:claimID technical specification.¶
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re:claimID is a decentralized, self-sovereign identity management system. It allows users to be in control over their digital identities without having to rely on central identity provider services (IdPs) in order to share personal data.¶
re:claimID is built upon the GNU Name System [GNS] for data sharing and storage. It leverages the zone privacy and key blinding properties of the name system in order to provide a secure sharing and authorization mechanism.¶
The system supports both "self-asserted" as well as third party asserted identity attributes. The assertion mechanisms are out of scope of this document.¶
The re:claimID system can used and integrated into the OpenID Connect protocol.¶
This document defines the normative wire format of resource records, resolution processes, cryptographic routines and security considerations for use by implementors.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].¶
An identity in re:claimID is defined through a zone in GNS. As such, the creation of a zone in GNS implicitly also creates a re:claimID identity.¶
A re:claimID identity attribute is stored in GNS under records of type "RECLAIM_ATTRIBUTE". An attribute consists of an identifier, an optional attestation identifier, a type, a flag, a name and data. The record format of a RECLAIM_ATTRIBUTE is as follows:¶
0 8 16 24 32 40 48 56 +-----+-----+-----+-----+-----+-----+-----+-----+ | TYPE | FLAG | +-----+-----+-----+-----+-----+-----+-----+-----+ | ID | | | | | | | +-----+-----+-----+-----+-----+-----+-----+-----+ | ATTESTATION | | | | | | | +-----+-----+-----+-----+-----+-----+-----+-----+ | NSIZE | DSIZE | +-----+-----+-----+-----+-----+-----+-----+-----+ / NAME + DATA / / / +-----------------------------------------------+
where:¶
A re:claimID credential is stored in GNS under records of type "RECLAIM_CREDENTIAL". A credential consists of an identifier, a type, a flag, a name and data. The record format of a RECLAIM_CREDENTIAL is as follows:¶
0 8 16 24 32 40 48 56 +-----+-----+-----+-----+-----+-----+-----+-----+ | TYPE | FLAG | +-----+-----+-----+-----+-----+-----+-----+-----+ | ID | | | | | | | +-----+-----+-----+-----+-----+-----+-----+-----+ | NSIZE | DSIZE | +-----+-----+-----+-----+-----+-----+-----+-----+ / NAME + DATA / / / +-----------------------------------------------+
where:¶
In order to share a set of identity attributes with a third party, re:claimID introduces the concept of "Tickets". A Ticket may be issued by a user for an identity to a relying party. The Ticket may then be used by the relying party to retrieve the shared attributes from the name system.¶
A ticket is a GNS name that points to information pertaining to the authorization given to the relying party. The ticket has the format:¶
ticket = "TID.IDENTITY.zkey" TID = *gnslabel IDENTITY = *gnslabel
The TID essentially serves as a shared secret between user and relying party. knowledge of the IDENTITY key and the TID allows the relying party to iteratively query attribute data in GNS. The record set under the TID label contains references to the shared attributes as well as any credential presentations which attest attribute values. The record set also includes the AUDIENCE key.¶
A RP resource record is stored in GNS under records of type "RECLAIM_RP". An RP reference is stored in GNS under the TID. The record format of a RECLAIM_RP is as follows:¶
0 8 16 24 32 40 48 56 +-----+-----+-----+-----+-----+-----+-----+-----+ | AUDIENCE KEY | | | | | | | +-----+-----+-----+-----+-----+-----+-----+-----+
where:¶
An attribute reference is stored in GNS under records of type "RECLAIM_ATTRIBUTE_REF". An attribute reference is stored in GNS under a label derived from a ticket ID. The reference points to an actual attribute ID. The record format of a RECLAIM_ATTRIBUTE_REF is as follows:¶
0 8 16 24 32 40 48 56 +-----+-----+-----+-----+-----+-----+-----+-----+ | ATTRIBUTE ID | | | | | | | +-----+-----+-----+-----+-----+-----+-----+-----+
where:¶
A re:claimID presentation is stored in GNS under records of type "RECLAIM_PRESENTATION". A presentation is derived from a credential and may contain only a subset of the attestations. The presentation construct is used to support selective disclosure of third party issued credentials. It consists of a type, a flag, a name and data. The record format of a RECLAIM_PRESENTATION is as follows:¶
0 8 16 24 32 40 48 56 +-----+-----+-----+-----+-----+-----+-----+-----+ | TYPE | FLAG | +-----+-----+-----+-----+-----+-----+-----+-----+ | ID | | | | | | | +-----+-----+-----+-----+-----+-----+-----+-----+ | NSIZE | DSIZE | +-----+-----+-----+-----+-----+-----+-----+-----+ / NAME + DATA / / / +-----------------------------------------------+
where:¶
All attribute names in re:claimID are encoded in UTF-8 [RFC3629].¶
The TID in a Ticket SHOULD have at least 256 bits of entropy. The TID could be generated by simply sampling 32 bytes of random data and encoding it using a suitable text encoding compatible with GNS labels such as Base64.¶
The TID MAY be derived using more sophisticated means in order to be able to relax security requirements on the exchange or storage of authorization metadata. One option is to derive the TID using ephemeral Diffie-Hellman. The user would first create an ephemeral key pair and calculate the TID in order to populate the GNS resource records:¶
CreateTid(AUDIENCE_PK): x := rand() ETK := X25519 (x, AUDIENCE_PK) dhs := X25519 (x, G) TID := Base64 (SHA-512 (dhs)) return (TID,ETK)¶
This allows to the user to only transfer the ETK which can in turn be used by the relying party to calculate the ticket identifier (TID) using its private key:¶
CalculateTid(AUDIENCE_SK,ETK): dhs := X25519 (AUDIENCE_SK, G) return TID := Base64 (SHA-512 (dhs))¶
GANA is requested to populate this registry as follows:¶
Number: 65549 Name: RECLAIM_TICKET Contact: N/A References: [This.I-D] Description: Ticket Number: 65549 Name: RECLAIM_ATTRIBUTE Contact: N/A References: [This.I-D] Description: Identity attribute Number: 65550 Name: RECLAIM_ATTRIBUTE_REF Contact: N/A References: [This.I-D] Description: Refrerence to identity attribute Number: 65551 Name: RECLAIM_OIDC_CLIENT Contact: N/A References: [This.I-D] Description: OIDC client description Number: 65552 Name: RECLAIM_OIDC_REDIRECT Contact: N/A References: [This.I-D] Description: OIDC client redirect(s) Number: 65553 Name: RECLAIM_CREDENTIAL Contact: N/A References: [This.I-D] Description: Credential Number: 65554 Name: RECLAIM_PRESENTATION Contact: N/A References: [This.I-D] Description: Credential presentation
GANA is requested to amend the "GNUnet Signature Purpose" registry as follows:¶
Purpose: 27 Name: RECLAIM_CODE_SIGN References: [This.I-D] Description: Signature in OIDC authorization code