Java and .NET interop on (RSA) signatures

Question

I'm signing some data on a .net-based smartcard and trying to verify that signature in a java environment - but without success.

Smartcard (c#):

RSACryptoServiceProvider rsaProvider = new RSACryptoServiceProvider(1024); // In a different method, rsaParams.Exponent and rsaParams.Modulus are set rsaProvider.ImportParameters(rsaParams); // Here I'm importing the key SHA1 sha1 = SHA1.Create(); byte[] signature = rsaProvider.SignData(data, sha1);

Client (Java):

Signature sig = Signature.getInstance("SHA1withRSA"); sig.initVerify(rsaPublicKey); // initiate the signature with public key sig.update(data); // update signature with the data that was signed by the card sig.verify(signedData); // Test card signature - this always returns false

I then tried to create the signature on the Java client (for testing) - and it turns out that the signature created on the Java client is different from the one created on the smartcard. I created it like this:

Signature sig = Signature.getInstance("SHA1withRSA"); sig.initSign(rsaPrivateKey); sig.update(data); locallySigned = sig.sign();

Now I understand that the signature is something like the hash of (passed data + the used algorithm). Is it possible that the implementations are not compatible here? Am I missing something else? Thanks!

PS: Yes, I verified that both input and output are transferred correctly from/to the card, that the key parameters are set and that input/output are exactly the same.

Edit: Key Generation in Java:

// Create a key-pair and install the private key on the card KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA"); SecureRandom random = SecureRandom.getInstance("SHA1PRNG", "SUN"); keyGen.initialize(1024, random); KeyPair keyPair = keyGen.genKeyPair(); privateKey = (RSAPrivateKey)keyPair.getPrivate(); publicKey = (RSAPublicKey)keyPair.getPublic();

and then I'm setting exp and mod of the private key on the card.

In Java, how are you generating the RSA public key?

Kevin
– Kevin

2009-10-21 18:21:50 +00:00
Commented Oct 21, 2009 at 18:21 — Kevin
– Kevin, Commented Oct 21, 2009 at 18:21

Rasmus Faber · Accepted Answer · 2009-10-21 18:32:36Z

3

// In a different method, rsaParams.Exponent and rsaParams.Modulus are set

To set the private exponent in an RSA key, you should use RSAParameters.D. RSAParameters.Exponent is for the public exponent.

answered Oct 21, 2009 at 18:32

Rasmus Faber

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2 Comments

wilth Over a year ago

Wow, are you serious? That would explain it ;-) Trying it out (setting Modulus and D), I'm getting a Cryptographic Exception when importing - according to the doc, I might miss some parameters in the RSAParameters. Anyone knows which ones are required?

wilth Over a year ago

It's waiting for the public exponent as well - once this is set it works. Thx a lot for the hint!

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