RSA encryption in Android and Java

Question

I would like to encrypt a String with RSA encryption. My public/private keys were generated and stored in DB. In android, I use this code:

public static String e         


        

Answer 1

It looks like you've been undone by relying on defaults. Never do that if you hope for interoperability.

Here are the two examples of mistakenly relying on defaults in your code that I've found.

final Cipher cipher = Cipher.getInstance("RSA");

The tranformation string is supposed to be of the form "algorithm/mode/padding" but you've left off the mode and padding specifications. As a result you got default values for those. The defaults are evidently different on Android and Oracle Java. You should always fully specify the transformation, for example:
final Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWITHSHA-256ANDMGF1PADDING");

Another bad example is cipherText = cipher.doFinal(text.getBytes());

In text.getBytes() you are relying on the no-args getBytes() method which uses the default charset for the platform. But this default charset differs on different platforms, and thus this is not portable. In almost all cases I've run across you should specify the UTF-8 charset. So the correct line would thus be
cipherText = cipher.doFinal(text.getBytes("UTF-8"));

and the correct string constructor to use to recreate the original string in the decrypt method is the String(byte [] data, String charsetName).