Issue using Key Binding in SD-JWT

[rober12]

Hello,

I’m trying to use Key Binding exactly as described in the documentation: URL

However, I’m unable to make it work and I keep running into the following errors:

• SDJWTException: Key Binding Verifier not found
• SDJWTException: Key Binding Signer not found

My current code does the following:

//  Holder creates selective presentation
const presentation = await sdjwt.present(credential, {
  firstname: true,
  id: true,
});

console.log("\n Selective presentation without KB:\n", presentation);

//  Holder constructs Key Binding JWT
const sdHash = crypto
  .createHash("sha256")
  .update(presentation)
  .digest("base64url");

const kbPayload = {
  iat: Math.floor(Date.now() / 1000),
  aud: "did:example:123",
  nonce: "k8vdf0nd6",
  sd_hash: sdHash,
};

const kbJwt = await new jose.SignJWT(kbPayload)
  .setProtectedHeader({ typ: "kb+jwt", alg: "ES256" })
  .sign(holderKeyPair.privateKey);

console.log("\n Key Binding JWT:\n", kbJwt);

//  Concatenate final presentation (SD-JWT + KB-JWT)
const finalPresentation = presentation + kbJwt;

console.log("\n Final presentation (with KB):\n", finalPresentation);

//  Verify presentation with required claims
const requiredClaims = ["firstname", "id"];
const verified = await sdjwt.verify(finalPresentation, {
  requiredClaimKeys: requiredClaims,
  keyBindingNonce: "k8vdf0nd6",
});
console.log(" SELECTIVE PRESENTATION VERIFIED:", verified);

I’ve also tried this approach:

//  Holder creates selective presentation
const kbPayload = {
  iat: Math.floor(Date.now() / 1000),
  aud: "https://example.com",
  nonce: "1234",
  custom: "data",
};

const presentedSdJwt = await sdjwt.present(
  credential,
  { id: true },
  {
    kb: {
      payload: kbPayload,
    },
  }
);

//  Verify presentation with required claims
const requiredClaims = ["firstname", "id"];
const verified = await sdjwt.verify(finalPresentation, {
  requiredClaimKeys: requiredClaims,
  keyBindingNonce: "1234",
});
console.log(" SELECTIVE PRESENTATION VERIFIED:", verified);

The first approach throws SDJWTException: Key Binding Verifier not found and the second one throws SDJWTException: Key Binding Signer not found.

Could you please help me understand what I’m doing wrong and how to properly use Key Binding?

Thank you very much in advance.

Best regards,

[cre8]

Hi @rober12
can you please also provide the code where you init your sdjwt instance like sdjwt = new new SDJwtInstance({ ... })

As seen here, I assume you haven't passed the functions for the kbSigner and kbVerifier. There is no default function to fall back so you get this errror: https://github.com/openwallet-foundation/sd-jwt-js/blob/main/docs/0.x/sdjwt-instance.md#configurations

Have a look at:

sd-jwt-js/examples/sd-jwt-example/kb.ts

Line 15 in c178fde

kbSigner: signer,

@lukasjhan we may update the docs to better point to the test files we have because then we know that the code is working.

[lukasjhan]

Yeah, good point. It's been quite log time since I wrote the docs.
I'll be working that on this weekend :)

[rober12]

Thank you very much @cre8 ,

Indeed, I was missing the following parameters in the SDJwtVcInstance:

kbSigner: holderSigner,
kbVerifier: holderVerifier,
kbSignAlg: "ES256",

With this, and by creating the presentation as indicated in the documentation, it now works correctly.

Thank you very much for the support.

Best regards.