Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
//License from project: Apache License 

import android.annotation.SuppressLint;
import android.support.annotation.NonNull;
import java.security.GeneralSecurityException;

import javax.crypto.Cipher;

import javax.crypto.spec.SecretKeySpec;

public class Main {
    /**
     * Computes an Ephemeral ID.
     * @param key                 AES key (Advertiser Identity Key). The first 16 bytes are used.
     * @param timeCounter         Advertiser time counter
     * @param rotationExponent    Advertiser rotation exponent (0 to 15)
     * @return Final ephemeral key of 16 bytes, of which only the first 8 bytes should be used.
     * @throws NoSuchPaddingException
     * @throws NoSuchAlgorithmException
     * @throws InvalidKeyException
     * @throws BadPaddingException
     * @throws IllegalBlockSizeException
     */
    @NonNull
    public static byte[] computeEID(byte[] key, int timeCounter, byte rotationExponent)
            throws GeneralSecurityException {
        //        String transformation = "AES/CBC/PKCS5Padding";
        String transformation = "AES/ECB/NoPadding";
        @SuppressLint("GetInstance")
        // spec says it has to be ECB, ignore lint warning
        Cipher aes = Cipher.getInstance(transformation);
        aes.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, 0, 16, "AES"));

        byte[] tempKey = aes
                .doFinal(new byte[] { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, (byte) 0xff,
                        0x00, 0x00, (byte) ((timeCounter >>> 24) & 0xff), (byte) ((timeCounter >>> 16) & 0xff) });

        // clear K lowest bits
        timeCounter = timeCounter >>> rotationExponent << rotationExponent;

        // reset cipher with a new encryption key
        aes.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(tempKey, "AES"));
        return aes.doFinal(new byte[] { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                rotationExponent, (byte) ((timeCounter >>> 24) & 0xff), (byte) ((timeCounter >>> 16) & 0xff),
                (byte) ((timeCounter >>> 8) & 0xff), (byte) (timeCounter & 0xff) });
    }
}