Semantic Web and Web 3.0 · class 11 · demo

A verifiable credential is signed RDF

examples/08-credential/credential.jsonld: read with its two contexts (local excerpts — there is no network) it is a graph of 13 triples. Signed here as sign-credential.mjs signs it, with a key made when this server started and kept only in memory. Then the verifier recomputes who signed what it was given.

validFrom a year earlier: the signature does NOT verify

expected signer (the proof's verificationMethod) 0xE1c8643C81B21181E648B3eF4Ce75D0229C34921
recovered from the signature and this content 0x846914f07cDA16417C3Dc32599e957078B949FB0

One field changed, so the canonical text changed, so the signature recovers a different address — any address but the issuer's.

The verifier's other checks

ok type, issuer, validity, status and proof present

Moving validFrom into the past silences this warning — and breaks the signature: the date is part of what the issuer signed.

The triples the verifier reads — the changed ones highlighted

The document shown below, read as RDF (lib/rdf.mjs, with the contexts of data/contexts/). With the demo's proof the graph has 14 triples; the key created is not in any context, so it gives no triple.

Subject	Predicate	Object
_:c0	a	cred:VerifiableCredential
_:c0	a	ufp:DiplomaUFP
_:c0	cred:issuer	<did:web:ufp.pt>
_:c0	cred:validFrom	"2026-07-20T00:00:00Z"^^xsd:dateTime
<did:key:z6Mk...>	ufp:degree	"MSc in Computer Engineering"
<did:key:z6Mk...>	ufp:grade	17
_:c0	cred:credentialSubject	<did:key:z6Mk...>
<https://ufp.pt/status/2027#42>	a	cred:StatusList2021
_:c0	cred:credentialStatus	<https://ufp.pt/status/2027#42>
_:c1	a	sec:DataIntegrityProof
_:c1	sec:cryptosuite	"ecdsa-secp256k1-jcs-2026-demo"
_:c1	sec:verificationMethod	<did:pkh:eip155:1:0xE1c8643C81B21181E648B3eF4Ce75D0229C34921>
_:c1	sec:proofValue	"0xa2096819b59db35dc3acae1eadf60cb8f4d5fc922afeb6d20b096e79bb5012025d9a0a54ca87375b2d8668bb2155f9574e21c82343c305553b0db163a6a359a31c"
_:c0	sec:proof	_:c1

What the verifier was given

{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://ufp.pt/contexts/diploma/v1"
  ],
  "type": [
    "VerifiableCredential",
    "DiplomaUFP"
  ],
  "issuer": "did:web:ufp.pt",
  "validFrom": "2026-07-20T00:00:00Z",
  "credentialSubject": {
    "id": "did:key:z6Mk...",
    "degree": "MSc in Computer Engineering",
    "grade": 17
  },
  "credentialStatus": {
    "type": "StatusList2021",
    "id": "https://ufp.pt/status/2027#42"
  },
  "proof": {
    "type": "DataIntegrityProof",
    "cryptosuite": "ecdsa-secp256k1-jcs-2026-demo",
    "created": "2026-11-01T13:17:13.132Z",
    "verificationMethod": "did:pkh:eip155:1:0xE1c8643C81B21181E648B3eF4Ce75D0229C34921",
    "proofValue": "0xa2096819b59db35dc3acae1eadf60cb8f4d5fc922afeb6d20b096e79bb5012025d9a0a54ca87375b2d8668bb2155f9574e21c82343c305553b0db163a6a359a31c"
  }
}

The class file: 13 triples

@prefix cred: <https://www.w3.org/2018/credentials#> .
@prefix ufp: <https://ufp.pt/vocabulary/diploma#> .
@prefix sec: <https://w3id.org/security#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .

_:c0 a cred:VerifiableCredential, ufp:DiplomaUFP ;
    cred:issuer <did:web:ufp.pt> ;
    cred:validFrom "2027-07-20T00:00:00Z"^^xsd:dateTime ;
    cred:credentialSubject <did:key:z6Mk...> ;
    cred:credentialStatus <https://ufp.pt/status/2027#42> ;
    sec:proof _:c1 .

<did:key:z6Mk...> ufp:degree "MSc in Computer Engineering" ;
    ufp:grade 17 .

<https://ufp.pt/status/2027#42> a cred:StatusList2021 .

_:c1 a sec:DataIntegrityProof ;
    sec:cryptosuite "eddsa-rdfc-2022" ;
    sec:proofValue "z3Mv..." .

An in-memory chain (the Ethereum virtual machine, @ethereumjs/evm), in this one process: no test network, no wallet, no keys, no money. Nothing a visitor does is kept.