The vocabulary of verifiable credentials.

assertionMethod

A DID document purpose binding that declares which verificationMethods are authorized to sign assertions — the purpose W3C VCs use.

authentication

A DID document purpose binding that declares which verificationMethods are authorized to authenticate the DID subject — separate from assertion signing.

controller

The DID document field declaring who has authority to update the DID — the legal and operational owner of the identifier.

Decentralized Identifier

Also: DID, W3C DID

A self-owned URL-like identifier whose associated public keys and services are declared in a resolvable DID document.

DID Document

Also: DID doc

A JSON-LD document that declares a DID's public keys, services, and relationships; served from a resolvable endpoint.

DID resolution

The process of dereferencing a DID to its DID document — the algorithm for following the identifier to its canonical keys and services.

did:cheqd

A DID method on the Cheqd blockchain — popular in the Self-Sovereign Identity (SSI) ecosystem, used by competitors like Dock.

did:key

A W3C DID method that encodes the public key directly in the identifier — no external document to resolve.

did:web

Also: did:web method

A W3C DID method that resolves an identifier to a DID document hosted at a well-known HTTPS path on the domain.

Key rotation

The practice of replacing a signing key with a new one, adding the new key to the DID document while keeping old credentials valid.

Service endpoint

A DID document field declaring services associated with a DID — used for discovery of issuer capabilities, OpenID4VCI endpoints, and similar.

verificationMethod

Also: verification method

A key entry inside a DID document that declares a public key a DID controls and what purposes it can be used for.

BBS+ signatures

Also: BBS signatures

A pairing-based signature scheme that supports selective disclosure and unlinkable presentations — popular in privacy-first VC deployments.

Canonicalization

The process of producing a deterministic byte representation of structured data — mandatory before hashing anything meant to be signed.

DER encoding

Also: ASN.1 DER, DER

The binary encoding format for ECDSA signatures as emitted by most HSMs and crypto libraries — ASN.1 Distinguished Encoding Rules.

ECDSA

Also: Elliptic Curve Digital Signature Algorithm

The Elliptic Curve Digital Signature Algorithm — the signature scheme LearnCoin uses over secp256k1, and the one Bitcoin and Ethereum use too.

Ed25519

Also: EdDSA Ed25519

An EdDSA signature scheme over the Curve25519 twist — faster than secp256k1 ECDSA, with deterministic nonces built in.

FIPS 140-2/140-3

Also: FIPS 140-2, FIPS 140-3, FIPS 140

The US federal certification standard for cryptographic modules — defines the HSM security levels LearnCoin's signing keys are certified against.

Google Cloud KMS

Also: GCP KMS, Cloud Key Management Service

Google Cloud's key-management service — the HSM-backed vault that holds every LearnCoin tenant's signing key.

Hardware Security Module

Also: HSM

A dedicated cryptographic device that performs key operations inside a tamper-resistant hardware boundary, with keys never exposed in software.

JOSE

Also: JSON Object Signing and Encryption

The IETF family of standards for signing and encrypting JSON — JWS, JWE, JWK, and JWT all live under this umbrella.

JWS

Also: JSON Web Signature, RFC 7515

The IETF standard for signing JSON payloads — the signature format that wraps JWTs and most OpenID Connect tokens.

JWT

Also: JSON Web Token, RFC 7519

A JSON payload format with standardized claims (iss, sub, exp, iat, aud) — when signed as a JWS, it becomes the most common bearer-token format on the web.

Linked Data Proofs

Also: LD Proofs, Data Integrity Proofs

A family of W3C proof formats that embed a cryptographic signature directly inside a JSON-LD document, rather than wrapping it externally.

Merkle root

The top hash in a Merkle tree — the single 32-byte value that cryptographically commits to every credential in a batch.

Merkle Tree

Also: Merkle root, hash tree

A binary tree of cryptographic hashes that lets a single root commit to an arbitrarily large set of items while keeping per-item proofs small.

MerkleProof2019

The Blockcerts v3 proof suite — a Linked Data Proof that commits a credential to a blockchain-anchored Merkle root.

Resource Description Framework

Also: RDF

The W3C data model underlying JSON-LD — statements expressed as subject-predicate-object triples that form a directed graph.

secp256k1

Also: secp256k1 curve

The elliptic curve used by Bitcoin, Ethereum, and most EVM chains — and the curve LearnCoin uses for every signing key.

SHA-256

Also: Secure Hash Algorithm 256, SHA-2

The 256-bit output variant of the SHA-2 family — the cryptographic hash function LearnCoin uses for leaf hashing, Merkle concatenation, and signature digests.

URDNA2015

Also: RDF Dataset Canonicalization 2015, URDNA

The RDF canonicalization algorithm LearnCoin uses to produce a deterministic byte representation of every credential before hashing.

Blockcerts v3

Also: Blockcerts

An open standard for blockchain-anchored verifiable credentials, originally created at MIT Media Lab and now stewarded by Hyland.

CTDL

Also: Credential Transparency Description Language

The US credential-transparency data model from Credential Engine — the parallel to ESCO for US labor-market credentials.

EBSI

Also: European Blockchain Services Infrastructure

The European Blockchain Services Infrastructure — the EU's shared public infrastructure for cross-border trust services including verifiable credentials.

eIDAS 2.0

Also: eIDAS 2, eIDAS Regulation

The EU regulation mandating European Digital Identity Wallets for every Member State, with verifiable-credential support baked in.

ESCO

Also: CEDEFOP ESCO, European Skills/Competences

The EU's multilingual taxonomy of skills, competences, and occupations — the standard alignment target for European credentials.

EUDI Wallet

Also: European Digital Identity Wallet, EUDI

The European Digital Identity Wallet — the EU's wallet specification for holding and presenting verifiable credentials, backed by the EUDI ARF.

ISO/IEC 18013-5 (mDL)

Also: mDL, ISO mDL, mobile driving licence

The ISO standard for mobile driver's licenses — the mDL format EUDI Wallet and most government digital-ID programs support.

JSON-LD

Also: JSON for Linking Data

A W3C-standardized JSON serialization for Linked Data. Every W3C Verifiable Credential is a JSON-LD document.

LearnCoin JSON-LD context

Also: schema.learncoin.me/v1/context.json

The LearnCoin-hosted JSON-LD context carrying LearnCoin extension fields (awardingBody, result, evidence, difficulty, actualDuration) — publication pending.

Open Badges 3.0

Also: OB 3.0, Open Badge 3.0

The 1EdTech specification for digital badges and micro-credentials, aligned with W3C Verifiable Credentials as of version 3.

OpenID Connect

Also: OIDC

The identity layer built on OAuth 2.0 — the protocol that powers 'Sign in with Google' and most modern federated authentication.

OpenID4VCI

Also: OpenID for Verifiable Credential Issuance

An OpenID Foundation spec that standardizes how a wallet holder pulls a verifiable credential from an issuer via OAuth-style flows.

OpenID4VP

Also: OpenID for Verifiable Presentations

The sibling of OpenID4VCI — a spec for how a wallet presents a verifiable credential to a verifier using OAuth-style flows.

SD-JWT

Also: Selective Disclosure JWT

The IETF draft for selective-disclosure JWTs — the likely EU-mandated format for EUDI Wallet selective-disclosure presentations.

VC-JWT

Also: Verifiable Credential JWT, JWT-VC

An alternative serialization of W3C Verifiable Credentials using signed JWTs instead of JSON-LD with Linked Data Proofs.

Base

Also: Base L2, Base (Coinbase)

Coinbase's open-source Ethereum Layer 2 built on the Optimism OP Stack — the network LearnCoin anchors every credential batch to.

Base Sepolia

Also: Base testnet

Base's test network — where LearnCoin's Developer-tier credentials anchor, free and unlimited, before graduating to Base mainnet.

Basescan

The Etherscan-family block explorer for Base — the primary UI for inspecting LearnCoin anchor transactions on-chain.

Calldata

Raw transaction payload data on an EVM chain — the space where LearnCoin writes Merkle roots as part of the anchor transaction.

EIP-4844

Also: proto-danksharding, blob transactions

The Ethereum upgrade that introduced 'blob' data — cheaper, ephemeral data availability that L2s use to post batches back to L1.

Ethereum

Also: Ethereum L1, Ethereum mainnet

The public, permissionless, smart-contract-capable blockchain that serves as LearnCoin's ultimate settlement substrate via Base L2.

Ethereum L1

Also: Ethereum Layer 1, Ethereum mainnet

The base Ethereum network — the L1 that Base (and every other OP-Stack rollup) settles back to via the withdrawal bridge.

Ethereum L2

Also: Ethereum Layer 2, L2, Layer 2 rollup

A blockchain that batches transactions and periodically settles them to Ethereum's Layer 1, inheriting L1's security at a fraction of the cost.

Fraud proof

An optimistic rollup's mechanism for challenging invalid state transitions — the 'challenge window' that anchors L2 security.

OP Stack

Also: Optimism OP Stack

The open-source modular software stack that powers Optimism and Base, defining how an Ethereum Layer 2 rollup is built.

Rollup

Also: rollup chain, optimistic rollup, zk-rollup

A Layer 2 architecture that executes transactions off-chain and posts compressed batches plus validity or fraud proofs back to Layer 1.

Validity proof

Also: ZK validity proof, SNARK proof

The cryptographic proof a zk-rollup posts to Layer 1 to prove its state transitions were correct — the zk counterpart to an optimistic fraud proof.

zk-rollup

Also: zero-knowledge rollup, validity rollup

A Layer 2 rollup that proves state validity cryptographically — faster finality than optimistic rollups, at the cost of more complex proving.

Data controller

Under GDPR, the entity that determines the purposes and means of processing personal data — one of the two primary GDPR roles alongside the processor.

Data processor

Under GDPR, the entity that processes personal data on behalf of a controller — LearnCoin is the processor for tenant-issued credentials.

Erasure

Also: GDPR erasure, right to erasure, right to be forgotten

A recipient's GDPR-granted right to have their personal data removed from LearnCoin's records — independent of whether the credential is still valid.

European Accessibility Act

Also: EAA

The EU directive mandating accessibility for digital products and services — enforces WCAG 2.2 AA conformance for EU public-sector procurement from 2025.

FERPA

Also: Family Educational Rights and Privacy Act

The US federal law governing privacy of student education records — LearnCoin's US institutional tenants are FERPA-bound.

GDPR

Also: General Data Protection Regulation

The EU regulation governing personal-data protection — the primary legal framework LearnCoin's architecture is designed around.

GDPR-aware schema

Also: GDPR schema split

LearnCoin's architectural pattern of storing pseudonymous identifiers on-chain and all PII off-chain under tenant-scoped RLS.

Personally Identifiable Information

Also: PII, personal data

Data that identifies or can be used to identify a natural person — legal name, email, government ID — subject to GDPR and similar regimes.

Privacy by design

Also: Privacy by Design, PbD

The principle that privacy protection is engineered into a system from the start — not bolted on. GDPR Article 25 codifies it as 'data protection by design and by default.'

Row Level Security

Also: RLS, tenant-scoped RLS

A PostgreSQL feature that enforces per-row access control at the database layer — LearnCoin uses it to isolate tenants' data.

Selective disclosure

Also: selective-disclosure VC

A credential-presentation technique that reveals only some signed claims while cryptographically proving the rest exist — no need to reveal or re-sign.

WCAG 2.2 AA

Also: Web Content Accessibility Guidelines 2.2

The W3C web-accessibility standard — LearnCoin commits to WCAG 2.2 Level AA conformance on every public credential surface from day one.