JWT signature verification

Question

I'm trying to validate the access token signature with my public key retrieved from an authentication server (OpenId).
The client get an access token from the same server and then request my Resource server API with it. Now I have to check its signature with the Spring Security library.
The access token has an "alg" : "RS256" attribute.
But the code below remains unsuccessful and I'm always getting the InvalidSignatureException...

import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.PublicKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.RSAPublicKeySpec;

import org.apache.commons.codec.binary.Base64;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.security.jwt.JwtHelper;
import org.springframework.security.jwt.crypto.sign.InvalidSignatureException;
import org.springframework.security.jwt.crypto.sign.RsaVerifier;

public class JWTValidation {

    private static final Logger logger = LoggerFactory.getLogger(JWTValidation.class);

    private static final String PUBLIC_KEY_MODULUS = "qOYyKKnoUpXd2qIj8A0tdumWwnDbVjXOVaPfiX5lxBvYEtgWPLknf1Nftdk371a7f1jD8SFFDxXnj-PPFx8qoNETOITvbR12uvWmS1J36B5Uo_ViHp7dC-GaZG_EdafyK0rxRPvK8b37NPXWhTggbxCZhYaqJUMb1t0xogDadEyM95lZweEXrwsJNzoyXiGnPfsRgy32TjOOXIMZnAMoj-osYd2WawymkRV6cteo3f8KMT72_kp8oG-kGm1s3ZooEfI3_9Z2jHVGWQLUWbmZKIrvjuUo2dhmqWWsNyTO3RsF4qyrRCpmZNawDf_GsioBTZ3vfPF_T58moH7cJ50Byw";
    private static final String PUBLIC_KEY_PUBLIC_EXPONENT = "AQAB";

    //Public key =
//  {
//      "keys":[
//          {
//            "kty":"RSA",
//            "use":"sig",
//            "kid":"DQr-GCc8rH3y5fkAuo0iau-ue-s",
//            "x5t":"DQr-GCc8rH3y5fkAuo0iau-ue-s",
//            "e":"AQAB",
//            "n":"qOYyKKnoUpXd2qIj8A0tdumWwnDbVjXOVaPfiX5lxBvYEtgWPLknf1Nftdk371a7f1jD8SFFDxXnj-PPFx8qoNETOITvbR12uvWmS1J36B5Uo_ViHp7dC-GaZG_EdafyK0rxRPvK8b37NPXWhTggbxCZhYaqJUMb1t0xogDadEyM95lZweEXrwsJNzoyXiGnPfsRgy32TjOOXIMZnAMoj-osYd2WawymkRV6cteo3f8KMT72_kp8oG-kGm1s3ZooEfI3_9Z2jHVGWQLUWbmZKIrvjuUo2dhmqWWsNyTO3RsF4qyrRCpmZNawDf_GsioBTZ3vfPF_T58moH7cJ50Byw",
//            "x5c":["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"]
//          }
//      ]
//  }

    //Access Token = base64url encoded String
    public boolean verifySignature(String accessToken){

        try {
            KeyFactory keyFactory = KeyFactory.getInstance("RSA");          
            Base64 decoder = new Base64(true);//URL-safe Base64 decoder

            BigInteger modulus = new BigInteger(decoder.decode(PUBLIC_KEY_MODULUS.getBytes()));
            BigInteger publicExponent = new BigInteger(decoder.decode(PUBLIC_KEY_PUBLIC_EXPONENT.getBytes()));

            RSAPublicKeySpec spec = new RSAPublicKeySpec(modulus, publicExponent);
            PublicKey newPublicKey = keyFactory.generatePublic(spec);

            RsaVerifier verif = new RsaVerifier((RSAPublicKey) newPublicKey, "SHA256withRSA");
            JwtHelper.decodeAndVerify(accessToken, verif);

        } catch (InvalidSignatureException e){
            logger.info(e.getMessage());
            return false;
        } catch (Exception e){
            logger.info(e.getMessage());
            return false;
        }

        return true;
    }
}

I also tried to use the online tool jwt.io but I've not been able to make it work (the signature remains invalid)
And for the other one ( tool_jwt ), the only way to have a valid signature is to choose the "default X.509 certificate RSA" with comments around my public key "x5c" value :

-----BEGIN CERTIFICATE-----
    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
-----END CERTIFICATE-----

So I don't know what to do now, which public key attribute should I use, and how to make it work ?

Thanks a lot for your help :)

Answer 1

I had the use the x509 key spec in addition to the RSA key spec

RSAPublicKeySpec spec = new RSAPublicKeySpec(new BigInteger(modulusBytes), new BigInteger(exponentBytes));
KeyFactory factory = KeyFactory.getInstance("RSA"); 
PublicKey key = factory.generatePublic(spec);


X509EncodedKeySpec X509publicKey = new X509EncodedKeySpec(key.getEncoded());
KeyFactory kf = KeyFactory.getInstance("RSA");
PublicKey pubKey64 = kf.generatePublic(X509publicKey);

This worked for both the auth0 and jwt.io libraries

Answer 2

To validate the signature online with jwt.io, you just need to put there the following json as a public key:

{
     "kty":"RSA",
     "kid":"DQr-GCc8rH3y5fkAuo0iau-ue-s",
     "e":"AQAB",
     "n":"qOYyKKnoUpXd2qIj8A0tdumWwnDbVjXOVaPfiX5lxBvYEtgWPLknf1Nftdk371a7f1jD8SFFDxXnj-PPFx8qoNETOITvbR12uvWmS1J36B5Uo_ViHp7dC-GaZG_EdafyK0rxRPvK8b37NPXWhTggbxCZhYaqJUMb1t0xogDadEyM95lZweEXrwsJNzoyXiGnPfsRgy32TjOOXIMZnAMoj-osYd2WawymkRV6cteo3f8KMT72_kp8oG-kGm1s3ZooEfI3_9Z2jHVGWQLUWbmZKIrvjuUo2dhmqWWsNyTO3RsF4qyrRCpmZNawDf_GsioBTZ3vfPF_T58moH7cJ50Byw"
}