Membership Credential (VMC)
A Verifiable Membership Credential attests to the membership of an entity in a community. It connects a person, device, or agent to a VTC — or one community to a VTN.
VMCs are Edge Credentials. The issuer is a C-DID (the community’s DID); the subject is an M-DID (a member’s DID) or another C-DID (when a VTN grants membership to a VTC).
Bidirectionality: Two VMCs = One Membership Edge
Membership in the DTG is symmetric: it isn’t enough for a community to claim a member, or for a member to claim a community. Membership is verified through a bi-directional pair of VMCs — one issued by the community to the member, and one issued by the member back to the community. Together the pair forms a complete membership edge between two entities (nodes) in the trust graph.
This mirrors the bidirectional model used for Relationship Credentials (VRCs): in the DTG, edges are always two-sided, attested by both ends.
Dual Purpose
VMCs serve two functions:
- Community membership — proving you belong to a specific community, enabling community-level policies (who can endorse, what trust thresholds apply)
- Personhood attestation — when the issuing community’s governance enforces real human personhood and one-membership-per-person rules, the VMC qualifies as a Personhood Credential (PHC)
Whether a VMC is a PHC is determined by the community’s trust registry, not by any structural difference in the credential. See personhood-credential for details.
VTN Membership
VMCs also express the relationship between VTNs and VTCs. A VTN issues a VMC to a VTC’s C-DID, and the VTC issues a VMC back, proving the community is a recognized member of the network. This enables hierarchical trust structures.
Community-Anchored ZKP
The VMC is the anchor for the community-anchored ZKP construction defined in spec §5.2. When both parties to a VRC hold VMCs from the same community, the holder can prove the existence of a relationship within the community’s governance context — without revealing the specific DIDs or other credential details. When the community’s VMCs qualify as PHCs, that personhood assurance carries forward into every relationship proven through this construction.
This is one of the two ZKP constructions defined for Edge Credentials; the other is the pairwise construction anchored to the VRC. See zero-knowledge-proofs for the full picture, including how to choose between them.
See also: zero-knowledge-proofs, personhood-credential, trust-registries, verifiable-trust-community, verifiable-trust-network, credential-categories