RSA Encryption with given public key (in Java)

Question

I'm looking for a Java sample how to do RSA Encryption with a given public key (I have it in base64 format, seems it is 1024 bit length).

Below is my code, but I have InvalidKeySpec exception.

String publicKey = "AJOnAeTfeU4K+do5QdBM2BQUhfrRI2rYf/Gk4a3jZJB2ewekgq2VgLNislBdql/glA39w0NjXZyTg0mW917JdUlHqKoQ9765pJc4aTjvX+3IxdFhteyO2jE3vKX1GgA3i3n6+sMBAJiT3ax57i68mbT+KAeP1AX9199aj2W4JZeP"; KeyFactory keyFactory = KeyFactory.getInstance("RSA"); byte[] res = new Base64Encoder().decode(publicKey.getBytes()); X509EncodedKeySpec KeySpec = new X509EncodedKeySpec(res); RSAPublicKey pubKey = (RSAPublicKey)keyFactory.generatePublic(KeySpec);  // here the exception occurs..  Cipher cipher = Cipher.getInstance("RSA/None/PKCS1Padding"); cipher.init(Cipher.ENCRYPT_MODE, pubKey); byte[] cipherData = cipher.doFinal(input.getBytes()); return cipherData; 

Please give me the sample,

Answer 1

Here's how I manage to encrypt a string with only a RSA public key.

First save the public key in PEM-format to the filename pubkey.pem

-----BEGIN PUBLIC KEY----- AJOnAeTfeU4K+do5QdBM2BQUhfrRI2rYf/Gk4... -----END PUBLIC KEY----- 

Find the public RSA key modulus

$ openssl rsa -pubin -in pubkey.pem -modulus -noout Modulus=F56D... 

Find the public RSA key Exponent

$ openssl rsa -pubin -in pubkey.pem -text -noout ... Exponent: 65537 (0x10001) 

Then insert them into the following code.

BigInteger modulus = new BigInteger("F56D...", 16); BigInteger pubExp = new BigInteger("010001", 16);  KeyFactory keyFactory = KeyFactory.getInstance("RSA"); RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(modulus, pubExp); RSAPublicKey key = (RSAPublicKey) keyFactory.generatePublic(pubKeySpec);  Cipher cipher = Cipher.getInstance("RSA/ECB/NoPadding"); cipher.init(Cipher.ENCRYPT_MODE, key);  byte[] cipherData = cipher.doFinal(text.getBytes());