Java equivalent of .NET RSACryptoServiceProvider with SHA-1

Question

I have data signing code in C #

RSACryptoServiceProvider rsa = new RSACryptoServiceProvider(); string PrivateKeyText = "<RSAKeyValue><Modulus>....</D></RSAKeyValue>"; rsa.FromXmlString(PrivateKeyText); string data = "my data"; byte[] SignedByteData = rsa.SignData(Encoding.UTF8.GetBytes(data), new SHA1CryptoServiceProvider()); 

and I want to reproduce the same code in Java (Android):

 String modulusElem = "..."; String expElem = "..."; byte[] expBytes = Base64.decode(expElem, Base64.DEFAULT); byte[] modulusBytes = Base64.decode(modulusElem, Base64.DEFAULT); BigInteger modulus = new BigInteger(1, modulusBytes); BigInteger exponent = new BigInteger(1, expBytes); try { KeyFactory factory = KeyFactory.getInstance("RSA"); Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1PADDING"); String data = "my data"; MessageDigest md = MessageDigest.getInstance("SHA-1"); byte[] hashedData = md.digest(data.getBytes("UTF-8")); RSAPublicKeySpec pubSpec = new RSAPublicKeySpec(modulus, exponent); PublicKey publicKey = factory.generatePublic(pubSpec); cipher.init(Cipher.ENCRYPT_MODE, publicKey); byte[] SignedByteData = cipher.doFinal(hashedData); } catch (Exception e){ } 

But I get inappropriate output byte arrays. Where am I mistaken and what should be the conversion used in Cipher.getInstance(...) ?

Answer 1

Use Signature.getInstance("SHA1withRSA") . Encryption is not the same as signature generation. Different filling mechanisms for one.

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Update from Afshin

Complete solution. Pay attention to the use of a private indicator, i.e. <D> , but rather on public <Exponent>

 String modulusElem = "..."; String dElem = "..."; byte[] modulusBytes = Base64.decode(modulusElem, Base64.DEFAULT); byte[] dBytes = Base64.decode(dElem, Base64.DEFAULT); BigInteger modulus = new BigInteger(1, modulusBytes); BigInteger d = new BigInteger(1, dBytes); String data = "my data"; try { Signature signature = Signature.getInstance("SHA1withRSA"); KeyFactory factory = KeyFactory.getInstance("RSA"); RSAPrivateKeySpec privateKeySpec = new RSAPrivateKeySpec(modulus, d); PrivateKey privateKey = factory.generatePrivate(privateKeySpec); signature.initSign(privateKey); signature.update(data.getBytes("UTF-8")); byte[] SignedByteData = signature.sign(); } catch(Exception e) { e.printStackTrace(); }