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dtg-credentials

Repo: github.com/OpenVTC/dtg-credentials

A Rust library implementing the Decentralized Trust Graph credential types. It provides the data structures and signing/verification logic for the Verifiable Credentials that form the edges of the trust graph.

What It Implements

The DTG Core Credentials specification from the Trust over IP Foundation’s DTG Working Group Credentials Task Force — v1.0 Working Draft 01 since crate version 0.2.0 (August 2026; 0.1.x tracked the informal v0.3). See DTG Credential Types for the full taxonomy.

Architecture

The library is compact — two source files and an example:

  • lib.rs — Core types: DTGCredential wrapper, DTGCommon (W3C VC structure, including the WD01 taskContext property), DTGCredentialType enum, CredentialSubject variants (Basic, Endorsement, Witness; RCard deprecated), signing/verification methods, VWC digest helpers (digest_multibase(), verify_digest())
  • create.rs — Builder methods for each credential type (new_vmc, new_vrc, new_vic, new_vpc, new_vec, new_vwc; new_rcard deprecated)

Usage

// Create a Persona Credential
let credential = DTGCredential::new_vpc(issuer_did, subject_did, valid_from, valid_until);
 
// Sign it
credential.sign(&secret, None).await?;
 
// Verify it
credential.verify_proof_with_public_key(&public_key)?;

The library supports both W3C VC 1.1 and 2.0, handling field name differences (issuanceDate/validFrom, expirationDate/validUntil) transparently via serde deserialization.

Dependencies

  • affinidi-data-integrity — W3C Data Integrity proof creation/verification (EdDSA JCS 2022)
  • affinidi-secrets-resolver — key management
  • serde — JSON serialization with camelCase and untagged enum dispatch
  • serde_json_canonicalizer (JCS / RFC 8785), sha2, multibase — VWC digest computation (since 0.2.0)

Provenance

Originally developed under LF-Decentralized-Trust-labs, migrated to the OpenVTC GitHub organization in spring 2026. Published on crates.io since 0.1.1 (2026-03-29; 0.1.0 was never published). MSRV 1.95.

Recent Development

After a quiet spring, the crate made its first semantic move in August 2026: 0.2.0 tracks the spec’s v1.0 Working Draft 01 (see dtg-credential-spec) — and in doing so fixed a live interoperability bug. It is part of the coordinated Cypress release (coordinated-releases; the Cypress and VTI-Cypress-RC-1 tags both point at the 0.2.0 HEAD; Banyan = RC-0 = 0.1.3). The VTI (#916) and openvtc (#205) moved onto 0.2 the same day — VMC/VEC/VIC bytes are unchanged, so the bump was painless for them.

v0.2.0 — 2026-08-10 — track DTG Core Credentials WD01 (#8, feat!; release notes #9)

  • taskContext added to DTGCommon (+ accessors). This was a real bug, not just a schema catch-up: DTGCommon lacked the field and had no deny_unknown_fields, so serde silently dropped taskContext on deserialise — and because sign() serialises the credential, issuers signed a document missing the field while verifiers hashed a different document than the one that was signed.
  • BREAKING: new_vwc(issuer, subject, valid_from, valid_until, task_context: String, digest: Option<String>, witness_context); deserialising a WitnessCredential without taskContext fails with the new DTGCredentialError::MissingTaskContext; new Canonicalization(String) error.
  • New VWC digest helpers digest_multibase() / verify_digest() — the digest covers the referenced VRC exactly as it stands, including its proof, over its JCS canonical form.
  • DTGCredentialType::RCard, CredentialSubject::RCard, CredentialSubjectRCard and new_rcard() deprecated (not removed) — the relationship card left the spec for a planned VDS companion.
  • ⚠ VWC digest divergence (flagged in the README/CHANGELOG, unresolved). WD01 says the digest MUST be encoded as sha256: + lowercase hex; the crate encodes it as a multibase base58btc multihash (z…), following the W3C digestMultibase convention. Same SHA-256 over the same JCS bytes — only the string encoding differs — but string comparison fails both ways, so verify_digest() rejects spec-conformant VWCs and conformant verifiers reject crate-produced ones. To be raised with the DTGWG. A second, undeclared gap: the crate still treats digest as Option (written against the PR #7 state); spec PR #14 two days later made it REQUIRED, so a VWC built with digest: None is now non-conformant.
  • History reconstructed: 0.1.2 and 0.1.3 had been published but never recorded; the async sign() change actually shipped in 0.1.1 (2026-03-29); placeholder dates replaced with crates.io dates; four rustdoc bare-URL warnings fixed.

v0.1.3 — 2026-06-07 — data-integrity 0.7 / TDK 0.7

  • affinidi-data-integrity 0.6 → 0.7
  • affinidi-tdk 0.6 → 0.7 (dev-dep)
  • sign_and_verify example migrated to the new TDK config builder (TDKConfigBuilder::new() → TDKConfig::builder())
  • MSRV bumped to 1.95.0

v0.1.2 — 2026-04-30

  • Bumped to affinidi-data-integrity 0.6 and migrated to its new API
  • CODEOWNERS for @OpenVTC/openvtc-maintainers

v0.1.1 and earlier — 2026-04 and prior

  • Dependency updates: affinidi-data-integrity 0.4 → 0.5, affinidi-tdk 0.5 → 0.6
  • sign() made async to align with upstream changes
  • Repository URL migration from LF-Decentralized-Trust-labs to OpenVTC
  • Crate publishing enablement

See also: dtg-credentials-overview, decentralized-trust-graph, verifiable-credentials

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