RSA Encryption with given public key (in Java)

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());