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autojs逆向与解密

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0. 背景

autojs是一个在Android编写、运行JavaScript代码的集成开发环境，包括代码补全的编辑器、单步调试、图形化设计，可构建为独立apk应用，也可连接电脑开发。

更新日志：参考 https://pro.autojs.org/docs/#/zh-cn/appChangeLog

autojs 4.1.1 alpha2: 为最后一个开源版本，不带加密功能。可以直接从https://github.com/hyb1996/Auto.js编译。

autojs pro 7: 带有离线加密和在线加密功能，但是已经不可以购买账号。autojs pro 7.0.4-1为最后一个版本。

autojs pro 8: 为目前比较新的版本，新增离线dex加密和snapshot加密两种加密方式，但是存在以下限制:

  • 某些软件上自动点击等无障碍功能不能生效，目前包括主流社交软件、直播软件、短视频软件、淘宝等（这个列表可能会动态更新）
  • 8.0不包含在线打包功能，以后可能考虑去掉离线加密功能。
autojs pro 8.7.5 离线dex加密
autojs pro 8.7.6 新增离线snapshot加密

autojs pro 9: 加密上无更新

1. encryptLevel为0(不加密)

方法一: frida hook解密

使用4.1.1版本，主动从实例中创建一个app样本，这里我打包了一个"代办事项"的apk，然后拖入jadx进行分析，在assets文件夹下面找到加密后的js和说明文件:

2022-08-27T17:47:18.png

{
  "assets": [],
  "build": {
    "build_id": "8E066D6B-1",
    "build_number": 1,
    "build_time": 1661513820823
  },
  "useFeatures": [],
  "main": "main.js",
  "name": "待办事项",
  "packageName": "com.example.script1",
  "scripts": {},
  "versionCode": 1,
  "versionName": "1.0.0"
}

js源代码加了密码，直接查找decrypt等关键词，定位到以下函数：

2022-08-27T04:54:20.png

接下来分析下这里是否能拿到解密后的js明文，采用frida进行函数调用的追踪：

function hook_class(className) {

    Java.perform(function () {
        Java.enumerateLoadedClasses({
            onMatch: function (name) {
                if (name.indexOf(className) != -1) {
                    traceClass(name)
                }

            },
            onComplete: function () {

            }
        })
    })

}

function printStack(name) {
    Java.perform(function () {
        var Exception = Java.use("java.lang.Exception");
        var ins = Exception.$new("Exception");
        var straces = ins.getStackTrace();
        if (straces != undefined && straces != null) {
            var strace = straces.toString();
            var replaceStr = strace.replace(/,/g, "\n");
            send("=============================" + name + " Stack start=======================");
            send(replaceStr);
            send("=============================" + name + " Stack end=======================\r\n");
            Exception.$dispose();
        }
    });
}


function traceClass(clsname) {
    try {
        var target = Java.use(clsname);
        var methods = target.class.getDeclaredMethods();
        methods.forEach(function (method) {
            var methodName = method.getName();
            var overloads = target[methodName].overloads;
            overloads.forEach(function (overload) {
                var proto = "(";
                overload.argumentTypes.forEach(function (type) {
                    proto += type.className + ", ";
                });
                if (proto.length > 1) {
                    proto = proto.substring(0, proto.length - 2);
                }
                proto += ")";
                console.log("hooking: " + clsname + "." + methodName + proto);
                overload.implementation = function () {
                    var args = [];
                    
                    for (var j = 0; j < arguments.length; j++) {
                        args[j] = arguments[j] + ""

                    }
                    var retval = this[methodName].apply(this, arguments);
                    console.log(clsname + '.' + methodName + proto + " args: ", args, "ret:", retval)
                    printStack(clsname + '.' + methodName)
                    return retval;
                }
            });
        });
    } catch (e) {
        send("'" + clsname + "' hook fail: " + e)
    }
}

function main() {
    hook_class("com.stardust.autojs.engine.encryption.ScriptEncryption")
}

setImmediate(main)

发现其在每次打开app的时候都会调用decrypt函数，将函数执行结果打印出来后，正好是js脚本。于是下面直接编写frida脚本拿解密结果即可。

index.js

function get_autojs_code() {
    Java.perform(function () {
        var clazz = Java.use("com.stardust.autojs.engine.encryption.ScriptEncryption");
        clazz.decrypt.implementation = function (arg1, arg2, arg3) {
            var result = this.decrypt(arg1, arg2, arg3);
            send(utf8ByteToUnicodeStr(result))
            return result;
        }
    })
}
function utf8ByteToUnicodeStr(utf8Bytes) {
    var unicodeStr = "";
    for (var pos = 0; pos < utf8Bytes.length;) {
        var flag = utf8Bytes[pos];
        var unicode = 0;
        if ((flag >>> 7) === 0) {
            unicodeStr += String.fromCharCode(utf8Bytes[pos]);
            pos += 1;

        } else if ((flag & 0xFC) === 0xFC) {
            unicode = (utf8Bytes[pos] & 0x3) << 30;
            unicode |= (utf8Bytes[pos + 1] & 0x3F) << 24;
            unicode |= (utf8Bytes[pos + 2] & 0x3F) << 18;
            unicode |= (utf8Bytes[pos + 3] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos + 4] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos + 5] & 0x3F);
            unicodeStr += String.fromCharCode(unicode);
            pos += 6;

        } else if ((flag & 0xF8) === 0xF8) {
            unicode = (utf8Bytes[pos] & 0x7) << 24;
            unicode |= (utf8Bytes[pos + 1] & 0x3F) << 18;
            unicode |= (utf8Bytes[pos + 2] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos + 3] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos + 4] & 0x3F);
            unicodeStr += String.fromCharCode(unicode);
            pos += 5;

        } else if ((flag & 0xF0) === 0xF0) {
            unicode = (utf8Bytes[pos] & 0xF) << 18;
            unicode |= (utf8Bytes[pos + 1] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos + 2] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos + 3] & 0x3F);
            unicodeStr += String.fromCharCode(unicode);
            pos += 4;

        } else if ((flag & 0xE0) === 0xE0) {
            unicode = (utf8Bytes[pos] & 0x1F) << 12;;
            unicode |= (utf8Bytes[pos + 1] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos + 2] & 0x3F);
            unicodeStr += String.fromCharCode(unicode);
            pos += 3;

        } else if ((flag & 0xC0) === 0xC0) { //110
            unicode = (utf8Bytes[pos] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos + 1] & 0x3F);
            unicodeStr += String.fromCharCode(unicode);
            pos += 2;

        } else {
            unicodeStr += String.fromCharCode(utf8Bytes[pos]);
            pos += 1;
        }
    }
    return unicodeStr;
}

index.py

## python 注入 frida js

import frida
import sys

target_app = "待办事项"

def on_message(message, data):
    if message['type'] == 'send':
        print("保存结果")
        with open(f"{target_app}.js", 'w' ,encoding='utf-8') as f:
            f.write(message["payload"])
    else:
        print(f"message: {message}")

jscode = open("index.js", encoding="utf-8").read()
device = frida.get_usb_device()
session = device.attach(target_app)
script = session.create_script(jscode)
script.on('message',on_message)
script.load()
sys.stdin.read()

方法二: 静态解密

通过frida hook分析的方式，可以看出js代码是采用了AES的方式进行的加解密，于是我们只需要找出iv和secret即可解密js。

下面尝试直接找出iv和secret，对所有的加解密函数进行hook：

var N_ENCRYPT_MODE = 1
var N_DECRYPT_MODE = 2

function showStacks() {
    var Exception = Java.use("java.lang.Exception");
    var ins = Exception.$new("Exception");
    var straces = ins.getStackTrace();

    if (undefined == straces || null == straces) {
        return;
    }

    console.log("============================= Stack strat=======================");
    console.log("");

    for (var i = 0; i < straces.length; i++) {
        var str = "   " + straces[i].toString();
        console.log(str);
    }

    console.log("");
    console.log("============================= Stack end=======================\r\n");
    Exception.$dispose();
}

//工具相关函数 
var base64EncodeChars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/',
    base64DecodeChars = new Array((-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), (-1), 62, (-1), (-1), (-1), 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, (-1), (-1), (-1), (-1), (-1), (-1), (-1), 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, (-1), (-1), (-1), (-1), (-1), (-1), 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, (-1), (-1), (-1), (-1), (-1));

function stringToBase64(e) {
    var r, a, c, h, o, t;
    for (c = e.length, a = 0, r = ''; a < c;) {
        if (h = 255 & e.charCodeAt(a++), a == c) {
            r += base64EncodeChars.charAt(h >> 2),
                r += base64EncodeChars.charAt((3 & h) << 4),
                r += '==';
            break
        }
        if (o = e.charCodeAt(a++), a == c) {
            r += base64EncodeChars.charAt(h >> 2),
                r += base64EncodeChars.charAt((3 & h) << 4 | (240 & o) >> 4),
                r += base64EncodeChars.charAt((15 & o) << 2),
                r += '=';
            break
        }
        t = e.charCodeAt(a++),
            r += base64EncodeChars.charAt(h >> 2),
            r += base64EncodeChars.charAt((3 & h) << 4 | (240 & o) >> 4),
            r += base64EncodeChars.charAt((15 & o) << 2 | (192 & t) >> 6),
            r += base64EncodeChars.charAt(63 & t)
    }
    return r
}
function base64ToString(e) {
    var r, a, c, h, o, t, d;
    for (t = e.length, o = 0, d = ''; o < t;) {
        do
            r = base64DecodeChars[255 & e.charCodeAt(o++)];
        while (o < t && r == -1);
        if (r == -1)
            break;
        do
            a = base64DecodeChars[255 & e.charCodeAt(o++)];
        while (o < t && a == -1);
        if (a == -1)
            break;
        d += String.fromCharCode(r << 2 | (48 & a) >> 4);
        do {
            if (c = 255 & e.charCodeAt(o++), 61 == c)
                return d;
            c = base64DecodeChars[c]
        } while (o < t && c == -1);
        if (c == -1)
            break;
        d += String.fromCharCode((15 & a) << 4 | (60 & c) >> 2);
        do {
            if (h = 255 & e.charCodeAt(o++), 61 == h)
                return d;
            h = base64DecodeChars[h]
        } while (o < t && h == -1);
        if (h == -1)
            break;
        d += String.fromCharCode((3 & c) << 6 | h)
    }
    return d
}
function hexToBase64(str) {
    return base64Encode(String.fromCharCode.apply(null, str.replace(/\r|\n/g, "").replace(/([\da-fA-F]{2}) ?/g, "0x$1 ").replace(/ +$/, "").split(" ")));
}
function base64ToHex(str) {
    for (var i = 0, bin = base64Decode(str.replace(/[ \r\n]+$/, "")), hex = []; i < bin.length; ++i) {
        var tmp = bin.charCodeAt(i).toString(16);
        if (tmp.length === 1)
            tmp = "0" + tmp;
        hex[hex.length] = tmp;
    }
    return hex.join("");
}
function hexToBytes(str) {
    var pos = 0;
    var len = str.length;
    if (len % 2 != 0) {
        return null;
    }
    len /= 2;
    var hexA = new Array();
    for (var i = 0; i < len; i++) {
        var s = str.substr(pos, 2);
        var v = parseInt(s, 16);
        hexA.push(v);
        pos += 2;
    }
    return hexA;
}
function bytesToHex(arr) {
    var str = '';
    var k, j;
    for (var i = 0; i < arr.length; i++) {
        k = arr[i];
        j = k;
        if (k < 0) {
            j = k + 256;
        }
        if (j < 16) {
            str += "0";
        }
        str += j.toString(16);
    }
    return str;
}
function stringToHex(str) {
    var val = "";
    for (var i = 0; i < str.length; i++) {
        if (val == "")
            val = str.charCodeAt(i).toString(16);
        else
            val += str.charCodeAt(i).toString(16);
    }
    return val
}
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 bytesToString(utf8Bytes) {
    var unicodeStr = "";
    for (var pos = 0; pos < utf8Bytes.length;) {
        var flag = utf8Bytes[pos];
        var unicode = 0;
        if ((flag >>> 7) === 0) {
            unicodeStr += String.fromCharCode(utf8Bytes[pos]);
            pos += 1;

        } else if ((flag & 0xFC) === 0xFC) {
            unicode = (utf8Bytes[pos] & 0x3) << 30;
            unicode |= (utf8Bytes[pos + 1] & 0x3F) << 24;
            unicode |= (utf8Bytes[pos + 2] & 0x3F) << 18;
            unicode |= (utf8Bytes[pos + 3] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos + 4] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos + 5] & 0x3F);
            unicodeStr += String.fromCharCode(unicode);
            pos += 6;

        } else if ((flag & 0xF8) === 0xF8) {
            unicode = (utf8Bytes[pos] & 0x7) << 24;
            unicode |= (utf8Bytes[pos + 1] & 0x3F) << 18;
            unicode |= (utf8Bytes[pos + 2] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos + 3] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos + 4] & 0x3F);
            unicodeStr += String.fromCharCode(unicode);
            pos += 5;

        } else if ((flag & 0xF0) === 0xF0) {
            unicode = (utf8Bytes[pos] & 0xF) << 18;
            unicode |= (utf8Bytes[pos + 1] & 0x3F) << 12;
            unicode |= (utf8Bytes[pos + 2] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos + 3] & 0x3F);
            unicodeStr += String.fromCharCode(unicode);
            pos += 4;

        } else if ((flag & 0xE0) === 0xE0) {
            unicode = (utf8Bytes[pos] & 0x1F) << 12;;
            unicode |= (utf8Bytes[pos + 1] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos + 2] & 0x3F);
            unicodeStr += String.fromCharCode(unicode);
            pos += 3;

        } else if ((flag & 0xC0) === 0xC0) { //110
            unicode = (utf8Bytes[pos] & 0x3F) << 6;
            unicode |= (utf8Bytes[pos + 1] & 0x3F);
            unicodeStr += String.fromCharCode(unicode);
            pos += 2;

        } else {
            unicodeStr += String.fromCharCode(utf8Bytes[pos]);
            pos += 1;
        }
    }
    return unicodeStr;
}
function bytesToBase64(e) {
    var r, a, c, h, o, t;
    for (c = e.length, a = 0, r = ''; a < c;) {
        if (h = 255 & e[a++], a == c) {
            r += base64EncodeChars.charAt(h >> 2),
                r += base64EncodeChars.charAt((3 & h) << 4),
                r += '==';
            break
        }
        if (o = e[a++], a == c) {
            r += base64EncodeChars.charAt(h >> 2),
                r += base64EncodeChars.charAt((3 & h) << 4 | (240 & o) >> 4),
                r += base64EncodeChars.charAt((15 & o) << 2),
                r += '=';
            break
        }
        t = e[a++],
            r += base64EncodeChars.charAt(h >> 2),
            r += base64EncodeChars.charAt((3 & h) << 4 | (240 & o) >> 4),
            r += base64EncodeChars.charAt((15 & o) << 2 | (192 & t) >> 6),
            r += base64EncodeChars.charAt(63 & t)
    }
    return r
}
function base64ToBytes(e) {
    var r, a, c, h, o, t, d;
    for (t = e.length, o = 0, d = []; o < t;) {
        do
            r = base64DecodeChars[255 & e.charCodeAt(o++)];
        while (o < t && r == -1);
        if (r == -1)
            break;
        do
            a = base64DecodeChars[255 & e.charCodeAt(o++)];
        while (o < t && a == -1);
        if (a == -1)
            break;
        d.push(r << 2 | (48 & a) >> 4);
        do {
            if (c = 255 & e.charCodeAt(o++), 61 == c)
                return d;
            c = base64DecodeChars[c]
        } while (o < t && c == -1);
        if (c == -1)
            break;
        d.push((15 & a) << 4 | (60 & c) >> 2);
        do {
            if (h = 255 & e.charCodeAt(o++), 61 == h)
                return d;
            h = base64DecodeChars[h]
        } while (o < t && h == -1);
        if (h == -1)
            break;
        d.push((3 & c) << 6 | h)
    }
    return d
}
//stringToBase64 stringToHex stringToBytes
//base64ToString base64ToHex base64ToBytes
//               hexToBase64  hexToBytes    
// bytesToBase64 bytesToHex bytesToString


Java.perform(function () {
    var secretKeySpec = Java.use('javax.crypto.spec.SecretKeySpec');
    secretKeySpec.$init.overload('[B', 'java.lang.String').implementation = function (a, b) {
        showStacks();
        var result = this.$init(a, b);
        console.log("======================================");
        console.log("算法名：" + b + "|str**:" + bytesToString(a));
        console.log("算法名：" + b + "|Hex**:" + bytesToHex(a));
        return result;
    }

    var DESKeySpec = Java.use('javax.crypto.spec.DESKeySpec');
    DESKeySpec.$init.overload('[B').implementation = function (a) {
        showStacks();
        var result = this.$init(a);
        console.log("======================================");
        var bytes_key_des = this.getKey();
        console.log("des**  |str " + bytesToString(bytes_key_des));
        console.log("des**  |hex " + bytesToHex(bytes_key_des));
        return result;
    }

    DESKeySpec.$init.overload('[B', 'int').implementation = function (a, b) {
        showStacks();
        var result = this.$init(a, b);
        console.log("======================================");
        var bytes_key_des = this.getKey();
        console.log("des**  |str " + bytesToString(bytes_key_des));
        console.log("des**  |hex " + bytesToHex(bytes_key_des));
        return result;
    }

    var mac = Java.use('javax.crypto.Mac');
    mac.getInstance.overload('java.lang.String').implementation = function (a) {
        showStacks();
        var result = this.getInstance(a);
        console.log("======================================");
        console.log("算法名：" + a);
        return result;
    }
    mac.update.overload('[B').implementation = function (a) {
        //showStacks();
        this.update(a);
        console.log("======================================");
        console.log("update:" + bytesToString(a))
    }
    mac.update.overload('[B', 'int', 'int').implementation = function (a, b, c) {
        //showStacks();
        this.update(a, b, c)
        console.log("======================================");
        console.log("update:" + bytesToString(a) + "|" + b + "|" + c);
    }
    mac.doFinal.overload().implementation = function () {
        //showStacks();
        var result = this.doFinal();
        console.log("======================================");
        console.log("doFinal结果: |str  :"     + bytesToString(result));
        console.log("doFinal结果: |hex  :"     + bytesToHex(result));
        console.log("doFinal结果: |base64  :"  + bytesToBase64(result));
        return result;
    }
    mac.doFinal.overload('[B').implementation = function (a) {
        //showStacks();
        var result = this.doFinal(a);
        console.log("======================================");
        console.log("doFinal参数: |str  :"     + bytesToString(a));
        console.log("doFinal结果: |str  :"     + bytesToString(result));
        console.log("doFinal结果: |hex  :"     + bytesToHex(result));
        console.log("doFinal结果: |base64  :"  + bytesToBase64(result));
        return result;
    }

    var md = Java.use('java.security.MessageDigest');
    md.getInstance.overload('java.lang.String', 'java.lang.String').implementation = function (a, b) {
        //showStacks();
        console.log("======================================");
        console.log("算法名：" + a);
        return this.getInstance(a, b);
    }
    md.getInstance.overload('java.lang.String').implementation = function (a) {
        //showStacks();
        console.log("======================================");
        console.log("算法名：" + a);
        return this.getInstance(a);
    }
    md.update.overload('[B').implementation = function (a) {
        //showStacks();
        console.log("======================================");
        console.log("update:" + bytesToString(a))
        return this.update(a);
    }
    md.update.overload('[B', 'int', 'int').implementation = function (a, b, c) {
        //showStacks();
        console.log("======================================");
        console.log("update:" + bytesToString(a) + "|" + b + "|" + c);
        return this.update(a, b, c);
    }
    md.digest.overload().implementation = function () {
        //showStacks();
        console.log("======================================");
        var result = this.digest();
        console.log("digest结果:" + bytesToHex(result));
        console.log("digest结果:" + bytesToBase64(result));
        return result;
    }
    md.digest.overload('[B').implementation = function (a) {
        //showStacks();
        console.log("======================================");
        console.log("digest参数:" + bytesToString(a));
        var result = this.digest(a);
        console.log("digest结果:" + bytesToHex(result));
        console.log("digest结果:" + bytesToBase64(result));
        return result;
    }

    var ivParameterSpec = Java.use('javax.crypto.spec.IvParameterSpec');
    ivParameterSpec.$init.overload('[B').implementation = function (a) {
        //showStacks();
        var result = this.$init(a);
        console.log("======================================");
        console.log("iv向量: |str:" + bytesToString(a));
        console.log("iv向量: |hex:" + bytesToHex(a));
        return result;
    }

    var cipher = Java.use('javax.crypto.Cipher');
    cipher.getInstance.overload('java.lang.String').implementation = function (a) {
        //showStacks();
        var result = this.getInstance(a);
        console.log("======================================");
        console.log("模式填充:" + a);
        return result;
    }
    cipher.init.overload('int', 'java.security.Key').implementation = function (a, b) {
        //showStacks();
        var result = this.init(a, b);
        console.log("======================================");
        if (N_ENCRYPT_MODE == a) 
        {
            console.log("init  | 加密模式");    
        }
        else if(N_DECRYPT_MODE == a)
        {
            console.log("init  | 解密模式");    
        }

        var bytes_key = b.getEncoded();
        console.log("init key:" + "|str**:" + bytesToString(bytes_key));
        console.log("init key:" + "|Hex**:" + bytesToHex(bytes_key));
        return result;
    }
    cipher.init.overload('int', 'java.security.cert.Certificate').implementation = function (a, b) {
        //showStacks();
        var result = this.init(a, b);
        console.log("======================================");
        
        if (N_ENCRYPT_MODE == a) 
        {
            console.log("init  | 加密模式");    
        }
        else if(N_DECRYPT_MODE == a)
        {
            console.log("init  | 解密模式");    
        }

        return result;
    }
    cipher.init.overload('int', 'java.security.Key', 'java.security.spec.AlgorithmParameterSpec').implementation = function (a, b, c) {
        //showStacks();
        var result = this.init(a, b, c);
        console.log("======================================");
        
        if (N_ENCRYPT_MODE == a) 
        {
            console.log("init  | 加密模式");    
        }
        else if(N_DECRYPT_MODE == a)
        {
            console.log("init  | 解密模式");    
        }
     
        var bytes_key = b.getEncoded();
        console.log("init key:" + "|str**:" + bytesToString(bytes_key));
        console.log("init key:" + "|Hex**:" + bytesToHex(bytes_key));

        return result;
    }
    cipher.init.overload('int', 'java.security.cert.Certificate', 'java.security.SecureRandom').implementation = function (a, b, c) {
        //showStacks();
        var result = this.init(a, b, c);
        if (N_ENCRYPT_MODE == a) 
        {
            console.log("init  | 加密模式");    
        }
        else if(N_DECRYPT_MODE == a)
        {
            console.log("init  | 解密模式");    
        }
        return result;
    }
    cipher.init.overload('int', 'java.security.Key', 'java.security.SecureRandom').implementation = function (a, b, c) {
        //showStacks();
        var result = this.init(a, b, c);
        if (N_ENCRYPT_MODE == a) 
        {
            console.log("init  | 加密模式");    
        }
        else if(N_DECRYPT_MODE == a)
        {
            console.log("init  | 解密模式");    
        }

         var bytes_key = b.getEncoded();
        console.log("init key:" + "|str**:" + bytesToString(bytes_key));
        console.log("init key:" + "|Hex**:" + bytesToHex(bytes_key));
        return result;
    }
    cipher.init.overload('int', 'java.security.Key', 'java.security.AlgorithmParameters').implementation = function (a, b, c) {
        //showStacks();
        var result = this.init(a, b, c);
        if (N_ENCRYPT_MODE == a) 
        {
            console.log("init  | 加密模式");    
        }
        else if(N_DECRYPT_MODE == a)
        {
            console.log("init  | 解密模式");    
        }

        var bytes_key = b.getEncoded();
        console.log("init key:" + "|str**:" + bytesToString(bytes_key));
        console.log("init key:" + "|Hex**:" + bytesToHex(bytes_key));
        return result;
    }
    cipher.init.overload('int', 'java.security.Key', 'java.security.AlgorithmParameters', 'java.security.SecureRandom').implementation = function (a, b, c, d) {
        //showStacks();
        var result = this.init(a, b, c, d);
        if (N_ENCRYPT_MODE == a) 
        {
            console.log("init  | 加密模式");    
        }
        else if(N_DECRYPT_MODE == a)
        {
            console.log("init  | 解密模式");    
        }

        var bytes_key = b.getEncoded();
        console.log("init key:" + "|str**:" + bytesToString(bytes_key));
        console.log("init key:" + "|Hex**:" + bytesToHex(bytes_key));
        return result;
    }
    cipher.init.overload('int', 'java.security.Key', 'java.security.spec.AlgorithmParameterSpec', 'java.security.SecureRandom').implementation = function (a, b, c, d) {
        //showStacks();
        var result = this.update(a, b, c, d);
        if (N_ENCRYPT_MODE == a) 
        {
            console.log("init  | 加密模式");    
        }
        else if(N_DECRYPT_MODE == a)
        {
            console.log("init  | 解密模式");    
        }

         var bytes_key = b.getEncoded();
        console.log("init key:" + "|str**:" + bytesToString(bytes_key));
        console.log("init key:" + "|Hex**:" + bytesToHex(bytes_key));
        return result;
    }

    cipher.update.overload('[B').implementation = function (a) {
        //showStacks();
        var result = this.update(a);
        console.log("======================================");
        console.log("update:" + bytesToString(a));
        return result;
    }
    cipher.update.overload('[B', 'int', 'int').implementation = function (a, b, c) {
        //showStacks();
        var result = this.update(a, b, c);
        console.log("======================================");
        console.log("update:" + bytesToString(a) + "|" + b + "|" + c);
        return result;
    }
    cipher.doFinal.overload().implementation = function () {
        //showStacks();
        var result = this.doFinal();
        console.log("======================================");
        console.log("doFinal结果: |str  :"     + bytesToString(result));
        console.log("doFinal结果: |hex  :"     + bytesToHex(result));
        console.log("doFinal结果: |base64  :"  + bytesToBase64(result));
        return result;
    }
    cipher.doFinal.overload('[B').implementation = function (a) {
        //showStacks();
        var result = this.doFinal(a);
        console.log("======================================");
        console.log("doFinal参数: |str  :"     + bytesToString(a));
        console.log("doFinal结果: |str  :"     + bytesToString(result));
        console.log("doFinal结果: |hex  :"     + bytesToHex(result));
        console.log("doFinal结果: |base64  :"  + bytesToBase64(result));
        return result;
    }

    var x509EncodedKeySpec = Java.use('java.security.spec.X509EncodedKeySpec');
    x509EncodedKeySpec.$init.overload('[B').implementation = function (a) {
        //showStacks();
        var result = this.$init(a);
        console.log("======================================");
        console.log("RSA**:" + bytesToBase64(a));
        return result;
    }

    var rSAPublicKeySpec = Java.use('java.security.spec.RSAPublicKeySpec');
    rSAPublicKeySpec.$init.overload('java.math.BigInteger', 'java.math.BigInteger').implementation = function (a, b) {
        //showStacks();
        var result = this.$init(a, b);
        console.log("======================================");
        //console.log("RSA**:" + bytesToBase64(a));
        console.log("RSA**N:" + a.toString(16));
        console.log("RSA**E:" + b.toString(16));
        return result;
    }

    var KeyPairGenerator = Java.use('java.security.KeyPairGenerator');
    KeyPairGenerator.generateKeyPair.implementation = function () 
    {
        //showStacks();
        var result = this.generateKeyPair();
        console.log("======================================");
        
        var str_private = result.getPrivate().getEncoded();
        var str_public = result.getPublic().getEncoded();
        console.log("公钥  |hex" + bytesToHex(str_public));
        console.log("私钥  |hex" + bytesToHex(str_private));

        return result;
    }

    KeyPairGenerator.genKeyPair.implementation = function () 
    {
        //showStacks();
        var result = this.genKeyPair();
        console.log("======================================");

        var str_private = result.getPrivate().getEncoded();
        var str_public = result.getPublic().getEncoded();
        console.log("公钥  |hex" + bytesToHex(str_public));
        console.log("私钥  |hex" + bytesToHex(str_private));

        return result;
    }
});

2022-08-27T17:58:44.png 2022-08-27T17:59:09.png

再结合

可以看出解密方式为：

AES/CBC/PKCS5Padding
key = MD5(packageName + versionName + main)
iv= MD5(build_id + name)前16位

编写出解密脚本为


from apkutils import APK
import zipfile
import sys
import json
from Crypto.Cipher import AES  
from base64 import b64decode, b64encode
import hashlib


class AESCipher:
    def __init__(self, secretkey: bytes, iv:bytes):
        self.key = secretkey  # 密钥
        self.iv = iv # 偏移量

    def pk5_decrypt(self, encrypted_text:bytes):
        """
        解密: aes解密
        :param encrypted_text : 已经加密的密文
        :return:
        """
        cipher = AES.new(key=self.key, mode=AES.MODE_CBC, IV=self.iv)
        decrypted_text = cipher.decrypt(encrypted_text)
        # 去除补位
        unpad = lambda s: s[:-ord(s[-1:])]

        return unpad(decrypted_text).decode('utf-8')

if __name__=="__main__":
    # apk = APK.from_file()

    zipfiles = zipfile.ZipFile("待办事项.apk")


    config = json.load(zipfiles.open("assets/project/project.json"))
    print(f"读取到project.json:{config}")
    build_id = config["build"]["build_id"]
    main = config["main"]
    package_name = config["packageName"]
    version_name = config["versionName"]
    name = config["name"]
    key = hashlib.md5(f"{package_name}{version_name}{main}".encode(encoding='UTF-8')).hexdigest()  # MD5(packageName + versionName + main)
    key = key.encode()
    iv = hashlib.md5(f"{build_id}{name}".encode(encoding='UTF-8')).hexdigest()[:16]   # MD5(build_id + name)前16位
    iv = iv.encode()
    print(f"key({type(key)}):{key}")

    
    print(f"iv:({type(iv)}):{iv}")
    aes = AESCipher(key, iv)

    namelist = zipfiles.namelist()  # 得到压缩包里所有文件
    print(f"下面解析apk的assets/project/文件")
    for name in namelist:
        if "assets/project/" in name and name.endswith(".js"):
            print(f"解密到{name}")
            data = zipfiles.open(name).read()
            decrypted_text = aes.pk5_decrypt(data[8:])  # 解密
            # print(decrypted_text)

2. encryptLevel为1

上面的情况是打包时没有选择加密的情况，下面测试加密的情况。通过autojs pro 7.0.4-1版本的autojs pro打包出一个新的app，选用了离线加密。

2022-08-27T18:17:54.png

打开project.json如下：

{
  "assets": [],
  "build": {
    "build_id": "39DB2720-1",
    "build_number": 1,
    "build_time": 1661624286327,
    "release": true
  },
  "encryptLevel": 1,
  "useFeatures": [],
  "launchConfig": {
    "displaySplash": true,
    "hideLogs": false,
    "splashText": "Powered by Auto.js Pro",
    "stableMode": false
  },
  "main": "main.js",
  "name": "拉出通知栏",
  "optimization": {
    "removeOpenCv": false,
    "unusedResources": false
  },
  "packageName": "com.example.script1661624194037",
  "scripts": {},
  "versionCode": 1,
  "versionName": "1.0.0"
}

可以看到encryptLevel为1，下面进行解密分析。

方法一: frida hook解密

分析后发现，和encryptLevel为0的hook方式一致，略。

方法二: 静态解密

还是通过trace所有aes加密函数的方式进行分析。发现密钥key变了，变成了一段乱码：

2022-08-28T16:11:32.png

于是静态分析发现以下代码：

com.stardust.autojs.engine.encryption.initFingerprint(ProjectConfig projectConfig)

2022-08-28T16:13:08.png

得出以下解密方式

AES/CBC/PKCS7Padding
iv= MD5(build_id + name)前16位
key = MD5(packageName + versionName + main)
然后通过iv和key加密一段字符串，密文为key2

然后通过iv和key2，即可解密js脚本。

3. encryptLevel为2、3

待分析

encryptLevel=3为snapshot加密，解密比较麻烦。

4. 通用脚本

针对encryptLevel为1以下的，通用的离线解密js脚本: https://github.com/saucer-man/autojs_reverse

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