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.
Another degree: the signature does NOT verify
expected signer (the proof's verificationMethod) 0xE1c8643C81B21181E648B3eF4Ce75D0229C34921
recovered from the signature and this content 0x760599860127DBc367a961c5b3E1326086F2e8Ea
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
warning it is not valid yet (validFrom 2027-07-20T00:00:00Z)
As in verify-credential.py: validFrom is in the future on purpose (the class README, note 4) — a credential has a validity period, and the verifier checks it. A valid signature does not make it valid today.
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 | "2027-07-20T00:00:00Z"^^xsd:dateTime |
| <did:key:z6Mk...> | ufp:degree | "PhD 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": "2027-07-20T00:00:00Z",
"credentialSubject": {
"id": "did:key:z6Mk...",
"degree": "PhD 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.