frida hook(CTF的示例WhyShouldIPay)

import frida, sys

jscode = """

     //字符串转换byte[]的方法
      function stringToBytes(str) {  
        var ch, st, re = []; 
        for (var i = 0; i < str.length; i++ ) { 
            ch = str.charCodeAt(i);  
            st = [];                 

           do {  
                st.push( ch & 0xFF );  
                ch = ch >> 8;          
            }    
            while ( ch );  
            re = re.concat( st.reverse() ); 
        }  
        return re;  
    } 
    //将byte[]转成String的方法
     function byteToString(arr) {  
        if(typeof arr === 'string') {  
            return arr;  
        }  
        var str = '',  
            _arr = arr;  
        for(var i = 0; i < _arr.length; i++) {  
            var one = _arr[i].toString(2),  
                v = one.match(/^1+?(?=0)/);  
            if(v && one.length == 8) {  
                var bytesLength = v[0].length;  
                var store = _arr[i].toString(2).slice(7 - bytesLength);  
                for(var st = 1; st < bytesLength; st++) {  
                    store += _arr[st + i].toString(2).slice(2);  
                }  
                str += String.fromCharCode(parseInt(store, 2));  
                i += bytesLength - 1;  
            } else {  
                str += String.fromCharCode(_arr[i]);  
            }  
        }  
        return str;  
    }

Java.perform(function () {

    var launcherActivity = Java.use('de.fraunhofer.sit.premiumapp.LauncherActivity');
    var mainActivity = Java.use('de.fraunhofer.sit.premiumapp.MainActivity')
    launcherActivity.getKey.implementation = function () {
        send("Hook Start...");
        var main = mainActivity.$new();
        var res = this.getMac();
        var bres = stringToBytes(res);
        send(bres);
        var bresponse = stringToBytes('LICENSEKEYOK');
        send(bresponse);
        var bkey = main.xor(bres,bresponse);
        send(bkey);
        var result = byteToString(bkey);
        send(result);
        send("Success!");
        return result;
    }
    launcherActivity.verifyClick.implementation = function (v) {
        this.showPremium(v);
    }
    //00:81:5b:22:4b:38
    //LICENSEKEYOK

});

"""

def message(message, data):
    if message["type"] == 'send':
        print("[*] {0}".format(message['payload']))
    else:
        print(message)

process = frida.get_remote_device().attach('de.fraunhofer.sit.premiumapp')
script= process.create_script(jscode)
script.on("message", message)
script.load()
sys.stdin.read()