XX客户端APP签名分析之算法分析篇

45300

将脱壳后的dex文件在jadx打开，由于脱壳后会产生多个dex，因此先用脚本合并一下比较方便。当然最新版jadx支持增加文件，也可以直接添加。
`

import os, sys

path = r'xxxx'# 文件夹目录
files = os.listdir(path)  
out_path =r'xxxxx'  
#路径
s = []
for file in files:  # 遍历文件夹
    if file.find("dex") > 0:  ## 查找dex 文件
        sh = f'jadx -j 1 -r -d {out_path} {path}\\{file}'
        print(sh)
        os.system(sh)`

同时使用抓包软件开始对app进行抓包，对于移动端的app抓包，证书的安装一直是一个很繁琐的问题，在这里推荐一款Magisk的模块Move Certificates,可以很方便的将用户证书移动到系统层，实现https的抓包。
这里主要的功能侧重点在bbsapi.domo.cn和class.domo.cn上，因为该app主要的功能点就是在这两个地址下。

查看一下数据包的内容，可以看到path中是包含sign值的

/newapi/live/square/live-count?noncestr=84140992&sign=47e714f977952ad75eb6eeb3165083dae93502b3&timestamp=1627008983764<

目标就是要找到这个sign值的生成算法。首先到jad中进行代码定位，为了降低逆向难度，可以选择从noncestr入手，进行搜索可能会简单一点，当然这只能是经验之谈，一切还是要以实际分析情况为准。

可以看一下如果搜索sign，会有多少结果。

继续看noncestr，看到搜索到了14个相关代码，根据类名来看，选择一个最最有可能的先看一下。

可以看到是有getSign函数在这个类下面的，采用直接hook这个函数也不是很现实，由于jadx的问题，是无法显示该函数下的代码，这个时候，可以采用直接hook该函数的系统加密函数的方法，来查看是否是直接采用了比如MD5,SHA1，Base64等等常规加密的方法，对于此，直接hook后查看输入和输出。
编写frida脚本进行测试一下。

update:appSignKey=ac6190d7dfaa77df726f0a82244d3eda68675ccd4e95de802f5042e91d15edc7bae3026d8f0fb2a8287446bb289563970264&noncestr=12520893&timestamp=1627023153533
digest:e2931f94fdf5cbad61d95bf23b192841a12f1a8c
可以看到上传数据的构成是appSignKey＋noncestr和timestamp构成。多次抓包发现appSignKey是一个固定值（只是class.domo.cn下的固定值，该app不同的网址采用不同的Key值）并且结果跟抓包数据完全一致。这时候主要的问题就是找到使用的默认算法。可以看到第一个调用的函数就是java.security.MessageDigest.digest(Native Method)，该类提供了消息摘要算法，如 MD5 或 SHA，的功能。因此可以模拟测试一下，看一下采用的是MD5还是SHA算法。

测试发现采用的是SHA1算法。noncestr就是随机8位数字组成，每次可以采用上一次所生成的，或者是自己生成即可。
noncestr算法还原。

Random random=new Random();

for(int i=0;i<8;i++){
    str.append(random.nextInt(10));
}

int num=Integer.parseInt(str.toString());
System.out.println(num);

此外，对于bbsapi.domo.cn，它的update是appSignKey=Wj8BI3VUZ6BuojAkqzBM3HWHNHv08xdZEtaksbRg6snnuLsvivwa8IvR6PvQ76H0IQQsqkIsa5OKJtg6QcBMfCblMMywgZaA8co&noncestr=63606047&timestamp=1627023164959采用了不同的key值来进行拼接。
总结
该app的签名算法还原后即为，key+noncestr+timestamp。之后进行SHA1加密，生成sign。最后附上frida hook代码

    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));
var stringToBase64 = function (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
}
var base64ToString = function (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
}


var hexToBytes = function (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;
}
var bytesToHex = function (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;
}
var stringToHex = function (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
}
var stringToBytes = function (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;
}

var bytesToString = function (arr) {
    var str = '';
    arr = new Uint8Array(arr);
    for (var i in arr) {
        str += String.fromCharCode(arr[i]);
    }
    return str;
}
var bytesToBase64 = function (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
}
var base64ToBytes = function (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
}


Java.perform(function () {

    function showStacks() {
        console.log(Java.use("android.util.Log").getStackTraceString(Java.use("java.lang.Exception").$new()));
    }


    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 + "|Dec密钥:" + bytesToString(a));
        console.log("算法名：" + b + "|Hex密钥:" + bytesToHex(a));
        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:" + bytesToHex(result));
        console.log("doFinal结果:" + bytesToBase64(result));
        return result;
    }
    mac.doFinal.overload('[B').implementation = function (a) {
        showStacks();
        var result = this.doFinal(a);
        console.log("======================================");
        console.log("doFinal参数:" + bytesToString(a));
        console.log("doFinal结果:" + bytesToHex(result));
        console.log("doFinal结果:" + 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:" + bytesToString(a));
        console.log("iv向量:" + 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.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:" + bytesToHex(result));
        console.log("doFinal结果:" + bytesToBase64(result));
        return result;
    }
    cipher.doFinal.overload('[B').implementation = function (a) {
        showStacks();
        var result = this.doFinal(a);
        console.log("======================================");
        console.log("doFinal参数:" + bytesToString(a));
        console.log("doFinal结果:" + bytesToHex(result));
        console.log("doFinal结果:" + 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密钥:" + 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密钥:" + bytesToBase64(a));
        console.log("RSA密钥N:" + a.toString(16));
        console.log("RSA密钥E:" + b.toString(16));
        return result;
    }

});

算法还原之后，下一篇将进行完结，打造bp插件，实现无缝衔接测试。

41269

搜索用"sign" 更好

45300

Rus
一般肯定是直接搜索sign的，我也是肯定第一个搜索sign，但是看到数量以后就再测试搜索其他的有没有关系，如果没有，肯定还是找sign来操作。

41269

psych1 嗯我的意思是直接搜“sign” 不是sign 然后jadx右键直接查找引用。