Generate x5c certificate chain from JWK

Question

I am using nimbus-jose-jwt 5.14 and I generated RSA key pair with the following code

    KeyPairGenerator gen = KeyPairGenerator.getInstance("RSA");
    gen.initialize(2048);
    KeyPair keyPair = gen.generateKeyPair();
    JWK jwk = new RSAKey.Builder((RSAPublicKey)keyPair.getPublic())
        .privateKey((RSAPrivateKey)keyPair.getPrivate())
        .keyUse(KeyUse.SIGNATURE)
        .keyID(UUID.randomUUID().toString())
        .build();

Now I need to expone some "metadata" about the public key:

• e
• kid
• kty
• n
• use
• x5c

How can I obtain x5c ? Is it possible to generate X509 certificate with this library? This field is null:

if (jwk.getX509CertChain() == null)

Benco

Related #74537770 – Cinerarium

Answer 1

You have generated a key pair, not a certificate. A certificate contains a public key but it is not derived from it, so you can't get a certificate directly from the public key.

To verify a JWT the recipient only needs the public key, so publishing the x5c is in fact unnecesary for this purpose

---

If you really want to publish a certificate, I suggest to generate it with OpenSSL and import the public key in your code to get the JWK parameters

openssl req -x509 -newkey rsa:2048 -keyout key.pem  -days 365 -out certificate.pem

Schultz

How can I generate a certificate with other tools? – Benco