Review

An instance of Cipher is used twice (the init() method is called again), which is an invalid operation.

creates a new instance of Cipher before the second init().

• missing/call

com/alibaba/druid/filter/config/ConfigTools.java

decrypt(PublicKey, String)

class ConfigTools {
	public static String decrypt(PublicKey publicKey, String cipherText)
			throws Exception {
		Cipher cipher = Cipher.getInstance("RSA");
		try {
			cipher.init(Cipher.DECRYPT_MODE, publicKey);
		} catch (InvalidKeyException e) {
			// for ibm jdk
			RSAPublicKey rsaPublicKey = (RSAPublicKey) publicKey;
			RSAPrivateKeySpec spec = new RSAPrivateKeySpec(rsaPublicKey.getModulus(), rsaPublicKey.getPublicExponent());
			Key fakePublicKey = KeyFactory.getInstance("RSA").generatePrivate(spec);
			cipher.init(Cipher.DECRYPT_MODE, fakePublicKey);
		}
		
		if (cipherText == null || cipherText.length() == 0) {
			return cipherText;
		}

		byte[] cipherBytes = Base64.base64ToByteArray(cipherText);
		byte[] plainBytes = cipher.doFinal(cipherBytes);

		return new String(plainBytes);
	}

}