import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class Launch {
	public static void main(String[] args) throws Exception {
		// API key
		String key = "--------------------------------";
		SecretKeySpec keySpec = new SecretKeySpec(readKey(key), "AES");
		
		// Message to encrypt
		String msg = "{}";
		
		// Initialize AES-CTR cipher
		Cipher aes = Cipher.getInstance("AES/CTR/NoPadding");
		
		// What is the IV for phpAES's AesCtr::encrypt?
		byte[] iv = new byte[16];
		
		IvParameterSpec ivSpec = new IvParameterSpec(iv);
		aes.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec);
		
		// Encrypt text
		byte[] ciphertext = aes.doFinal(msg.getBytes());
		
		// Print result
		System.out.println("Encrypted text: " + byteArrayToHex(ciphertext));
	}
	
	// Transforms the key from a hex-formatted String to a byte array
	public static byte[] readKey(String key) throws Exception {
		byte[] returnValue;
		
		if(key.length() != 32 && key.length() != 48 && key.length() != 64) {
			throw new Exception("Wrong key size (only 128, 192 and 256-bit keys are accepted).");
		}
		
		for(char c : key.toCharArray()) {
			if((c < '0' || c > '9') && (c < 'a' || c > 'f') && (c < 'A' || c > 'F')) {
				throw new Exception("Wrong character detected in key (expected hex string).");
			}
		}
		
		returnValue = new byte[key.length() / 2];
		
		for(int i = 0; i < key.length(); i += 2) {
			returnValue[i / 2] = (byte)((getHexDigitValue(key.charAt(i)) << 4) | getHexDigitValue(key.charAt(i + 1)));
		}
		
		return returnValue;
	}
	
	// Gets the value of a hex digit
	public static int getHexDigitValue(char c) {
		if(c >= '0' && c <= '9') {
			return c - '0';
		} else if(c >= 'a' && c <= 'f') {
			return c - 'a' + 10;
		} else {
			return c - 'A' + 10;
		}
	}
	
	// Returns the string representation of a byte array
	public static String byteArrayToHex(byte[] byteArray) {
		StringBuilder sb = new StringBuilder();
		
		for(byte b : byteArray) {
			sb.append(String.format("%02x", b));
		}
		
		return sb.toString();
	}
}