Java – RSA encrypt with base64 encoded public key in Android

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How to do RSA encryption of byte array with base-64 encoded public key?

After reading the couple of articles( of google search ) on how to do RSA encryption in Java, found the following snippet 

public byte[] rsaEncrypt(byte[] data) {
  PublicKey pubKey = readKeyFromFile("/public.key");
  Cipher cipher = Cipher.getInstance("RSA");
  cipher.init(Cipher.ENCRYPT_MODE, pubKey);
  byte[] cipherData = cipher.doFinal(src);
  return cipherData;
}

I have public key as a base64 encoded string (126 characters), How do i create 'PublicKey' with the encoded string and use it with Cipher.

Best Answer

Your base64 string is possibly an X509EncodedKeySpec. I can only guess. If so, you should base64 decode the string to obtain a byte []. Then construct an X509EncodedKeySpec from this byte []. Then create an instance of an RSA KeyFactory, and use the generatePublic() method of this KeyFactory to obtain a PublicKey. This public key can then be passed to Cipher.init().

Note: to perform base64 decoding use either the apache commons codec, or the Harder base64 decoder.

UPDATE March 8, 2017: In better-late-than-never news, Java 8 now includes a Base64 encoding/decoding class, java.util.Base64

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