Convert java.security "NONEwithRSA" signature into BouncyCastle lightweight API

Question

I need to convert Java app into C# and therefore need to migrate from java.security API into BouncyCastle lightweight API.

My working code (java.security) looks like this:

private byte[] computeSignature(byte[] message, PrivateKey key) {
    Signature signature = Signature.getInstance("NONEwithRSA");
    signature.initSign(privateKey);
    signature.update(message);
    return signature.sign();
}

This is my verification:

private void verifySignature(byte[] signature, byte[] message, PublicKey publicKey) {
    Signature signature = Signature.getInstance("NONEwithRSA");
    signature.initVerify(publicKey);
    signature.update(message);
    System.out.println(signer.verify(result) ? "OK" : "FAIL");
}

Now I am trying to migrate it to BC like this:

1. problem with NONEwithRSA algorithm which doesn't exist (not sure how to add it)

   private byte[] computeSignature(byte[] message, AsymmetricKeyParameter key) {
       AlgorithmIdentifier sigAlgId = new DefaultSignatureAlgorithmIdentifierFinder().find("NONEwithRSA");
       AlgorithmIdentifier digAlgId = new DefaultDigestAlgorithmIdentifierFinder().find(sigAlgId);
       ContentSigner signer = new BcRSAContentSignerBuilder(sigAlgId, digAlgId).build(key);
       signer.getOutputStream().write(Arrays.copyOf(message, message.length), 0, message.length);
       byte[] signature = signer.getSignature();
   }
   

2. doesn't provide good signature

   private byte[] computeSignature(byte[] message, AsymmetricKeyParameter privateKey) {
       Signer signer = new GenericSigner(new RSAEngine(), new NullDigest());
       signer.init(true, privateKey);
       signer.update(message, 0, message.length);
       return signer.generateSignature();
   }
   

Do you have any suggestions? Or is it even possible to migrate the NONEwithRSA algorithm into BC LW API? I assume that I need to write my own Signer, but as a newb to BC and with the BC documentation I can't handle this on my own.

Answer 1

Try this:

RSABlindedEngine engine = new RSABlindedEngine();
PKCS1Encoding paddedEngine = new PKCS1Encoding(engine);
paddedEngine.init(true, privateKey);
return paddedEngine.processBlock(message, 0, message.length);