DTG Credential Specification (ToIP DTGWG)

Repo: github.com/trustoverip/dtgwg-cred-tf

The authoritative specification for the Decentralized Trust Graph credential family, maintained by the Trust over IP Foundation’s DTG Working Group Credential Task Force. This is the definitive source for DTG credential semantics — what each credential type means, how it’s constructed, what proofs it supports, and how the wider trust graph composes from them. Implementations track this spec; where the wiki and the spec disagree, the spec wins.

The repo contains prose specifications in Markdown — no code. The wiki entity for the implementation that tracks this spec is dtg-credentials; for the conceptual taxonomy it defines, see dtg-credentials-overview.

Contents

• dtg.md — Core specification: credential type hierarchy, DID taxonomy, credential subjects, W3C VC v1.1/v2.0 support, ZKP constructions, personhood definition, trust registry references
• use_cases.md — Structured use cases: identity/sybil resistance, social capital, competence/reputation, persona management, advanced composite proofs
• witnessed_vrc_flow.md — Five-phase Witnessed Session-Based VRC Exchange protocol (v0.2)
• README.md — Index linking to spec, external documents (First Person Project Whitepaper, VTC Bootstrapping Process, DTG Glossary)

Wiki pages derived from this spec

• credential-categories — The four functional categories (Edge, Invitation, Annotation, VDS)
• did-types — The formal DID taxonomy (C-DID, M-DID, R-DID, P-DID, W-DID)
• trust-registries — Governance layer that determines PHC status and policies
• verifiable-trust-network — VTN concept (VTN → VTC hierarchy)
• witnessed-vrc-exchange — The five-phase witnessed exchange protocol
• persona-credential — VPC and the “Banksy Maneuver”
• invitation-credential — VIC with issuer policy details
• zero-knowledge-proofs — Pairwise vs community-anchored ZKP constructions; ZKPs by default
• Plus updates to personhood-credential, membership-credential, relationship-credential, dtg-credentials-overview, decentralized-trust-graph, and others

Recent Development

The spec is at v0.3; recent activity is per-PR. (PR numbers serve the role of version identifiers below since the spec version itself hasn’t bumped.)

PR #33 — 2026-05-08 — Split VRC/VMC ZKP proofs into pairwise and community-anchored constructions

• The old single “Zero-Knowledge Proof Requirements” subsection (under VRC) is replaced by two distinct constructions:
  • Pairwise ZKP (under VRC §5.1) — available to any two VRC holders, regardless of shared community membership; selectively discloses P-DIDs while hiding R-DIDs
  • Community-Anchored ZKP (under VMC §5.2) — requires both parties to hold VMCs from the same community; the three-part proof (VRC + VMC + same C-DID) is preserved but reframed as one option among several
• Section 5 reordered: VRC (5.1) now precedes VMC (5.2)
• Overview rewritten: DTG credentials are W3C-compliant VCs that MAY use standard presentation but SHOULD use ZKPs whenever privacy preservation is desired (citing Adler et al. 2024 — Personhood Credentials)
• New guidance: implementations SHOULD make ZKP presentation the default
• Privacy Considerations gained a “ZKPs by default” bullet
• Reflected in zero-knowledge-proofs, relationship-credential, membership-credential, persona-credential, credential-categories, dtg-credentials-overview

PR #31 — 2026-04-30 — Bidirectional Edge Credentials

• Both Edge Credentials reframed as edges between existing entities rather than node-creating or directional constructs
• VMC — “attests to the membership of an entity in a community; membership is verified through a bi-directional pair of VMCs”
• VRC — “attests to a relationship between two entities; the relationship is verified through a bi-directional pair of VRCs”
• Previously: VMCs were described as creating nodes and VRCs as creating directed edges
• Reflected in decentralized-trust-graph, membership-credential, relationship-credential, credential-categories, dtg-credentials-overview, verifiable-trust-network

See also: dtg-credentials (the Rust implementation), dtg-credentials-overview (the credential taxonomy as currently in the wiki).