> For the complete documentation index, see [llms.txt](https://docs.zetrix.com/en/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zetrix.com/en/developer-resources/agentic-wallet/architecture/key-terms.md).

# Key terms

**VC (Verifiable Credential)**, a tamper-proof, issuer-signed credential (W3C data model). In Zetrix it is dual-signed by the issuer with Ed25519 and BBS+ keys, which enables selective disclosure later.

**VP (Verifiable Presentation)**, the object the holder presents to a verifier, wrapping one or more VCs plus proofs bound to the verifier's challenge.

**DID / ZID**, a Decentralised Identifier; the Zetrix variant (`did:zid:…`) resolves to a DID document on-chain that carries the subject's public keys.

**DCQL (Digital Credentials Query Language)**, the JSON query a verifier uses to state which credential and which claims/constraints it needs. This is where a proof's required conditions are defined.

**BBS+ selective disclosure**, reveals only chosen claims from a VC while keeping the issuer signature verifiable. Producing it is a public-key re-randomisation of the issuer's signature, it needs no holder secret.

**Bulletproof range proof (BulletproofRangeProof2021)**, proves a numeric claim lies in a range (e.g. age ≥ 18) without revealing the value.

**Holder binding**, an Ed25519Signature2020 over the verifier's nonce, signed inside the HSM, proving the presenter controls the holder key. This is the only private-key operation the wallet performs during a proof.

**HSM (softHSM for the POC)**, PKCS#11 security module holding the holder key; interface-compatible with the future ms-zetrix hardware HSM (cutover is config-only).