byte[] expBytes = Base64.decodeBase64(exponentElem.getText().trim())); byte[] modBytes = Base64.decodeBase64(modulusElem.getText().trim()); byte[] dBytes = Base64.decodeBase64(dElem.getText().trim()); BigInteger modules = new BigInteger(1, modBytes); BigInteger exponent = new BigInteger(1, expBytes); BigInteger d = new BigInteger(1, dBytes); KeyFactory factory = KeyFactory.getInstance("RSA"); Cipher cipher = Cipher.getInstance("RSA"); String input = "test"; RSAPublicKeySpec pubSpec = new RSAPublicKeySpec(modules, exponent); PublicKey pubKey = factory.generatePublic(pubSpec); cipher.init(Cipher.ENCRYPT_MODE, pubKey); byte[] encrypted = cipher.doFinal(input.getBytes("UTF-8")); System.out.println("encrypted: " + new String(encrypted)); RSAPrivateKeySpec privSpec = new RSAPrivateKeySpec(modules, d); PrivateKey privKey = factory.generatePrivate(privSpec); cipher.init(Cipher.DECRYPT_MODE, privKey); byte[] decrypted = cipher.doFinal(encrypted); System.out.println("decrypted: " + new String(decrypted));