mtgsig1.2简单分析

{
 "a1": "1.2",        # 加密版本
 "a2": new Date().valueOf() - serverTimeDiff,       # 加密过程中用到的时间戳. 这次服主变坏了, 时间戳需要减去一个 serverTimeDiff(见a3) !  
 "a3": "这是把xxx信息加密后提交给服务器, 服主校验成功后返回的一个dfpId",      # dfpId. 服务器返回的dfpId数据包里, 有一个serverTimestamp字段. serverTimeDiff = serverTimestamp - Date.now()
 "a4": "一个长48位的加密结果",                      #  a5, a2以及一小段jsvmp运行后, 输出a4
 "a5": "一个长320位的加密结果",                       # a2, a6, 以及下面的Ln, 计算后输出a5
 "a6": "w1.2xxxxx这一段长512xxxxxxx",        # w1.2 + 客户端环境的加密结果
 "a7": wx["getAccountInfoSync"]().miniProgram.appId,     # 小程序id
 "x0": 3,   # 源代码写死
 "d1": md5ToHex(j)      #  a1, a2, a3, a4, a7以及上面加密过程中出现的一些数组, 经过运算后, 输出d1
}
 
Ln = {
"b1": {appId: "小程序id",  envVersion: "release", version: "微信版本号"},
"b2": "一个url",
"b6": "微信的openId",    # 这个玩意儿可以考虑置空
"b7": Math.floor(Date.now() / 1e3),
"b8": "17"    # 不重要, 1-20给个随机值就行
}

PS:  基于某评微信小程序的guard.js文件, 且文件经过简单的ast脱混淆.
1. 收集的环境

Ne = {
                DFP: ["app", "dfpid", "filetime", "fpv", "localid", "system", "timestamp", "ext", "sessionId"],
                system: ["accelerometer", "albumAuthorized", "BatteryInfo", "batteryLevel", "Beacons", "benchmarkLevel", "bluetoothEnabled", "brand", "brightness", "cameraAuthorized", "compass", "deviceOrientation", "devicePixelRatio", "enableDebug", "errMsg", "fontSizeSetting", "language", "LaunchOptionsSync", "locationAuthorized", "locationEnabled", "locationReducedAccuracy", "microphoneAuthorized", "model", "networkType", "notificationAlertAuthorized", "notificationAuthorized", "notificationBadgeAuthorized", "notificationSoundAuthorized", "pixelRatio", "platform", "safeArea", "screenHeight", "screenTop", "screenWidth", "SDKVersion", "statusBarHeight", "system", "version", "wifiEnabled", "WifiInfo", "windowHeight", "windowWidth"],
                BatteryInfo: ["errMsg", "isCharging", "level"],
                safeArea: ["left", "right", "top", "bottom", "width", "height"],
                WifiInfo: ["SSID", "BSSID", "autoJoined", "signalStrength", "justJoined", "secure", "frequency"]
            }

1.1 环境加密逻辑(a6). 主要是找到收集了哪些环境, 以及环境对应的值.

加密函数中只有常见的加密运算符, 没有检测环境的异常分支或其他坑. 所以逆向中遇到的加密函数直接 复制粘贴到自己的代码里就好. 譬如:

vn = {
        gzipSync: R,
        compressSync: R,
        strToU8: function (e, n) {
                var a = e.length;
                if (!n && "undefined" != typeof TextEncoder) return new TextEncoder().encode(e);
 
                for (var t = new Je(e.length + (e.length >>> 1)), c = 0, r = function (e) {
                        t[c++] = e;
                }, f = 0; f < a; ++f) {
                        if (c + 5 > t.length) {
                                var o = new Je(c + 8 + (a - f << 1));
                                o.set(t), t = o;
                        }
 
                        128 > (o = e.charCodeAt(f)) || n ? r(o) : 2048 > o ? (r(192 | o >>> 6), r(128 | 63 & o)) : 55295 < o && 57344 > o ? (r(240 | (o = 65536 + (1047552 & o) | 1023 & e.charCodeAt(++f)) >>> 18), r(128 | o >>> 12 & 63), r(128 | o >>> 6 & 63), r(128 | 63 & o)) : (r(224 | o >>> 12), r(128 | o >>> 6 & 63), r(128 | 63 & o));
                }
 
                return nn(t, 0, c);
        }
};
function R(e, n) {
        void 0 === n && (n = {});
        var a = pn(),
                t = e.length;
        a.p(e);
        var c = (e = ln(e, n, 10 + (n.filename && n.filename.length + 1 || 0), 8)).length,
                r = n;
        if (n = r.filename, e[0] = 31, e[1] = 139, e[2] = 8, e[8] = 2 > r.level ? 4 : 9 == r.level ? 2 : 0, e[9] = 3, 0 != r.mtime && gn(e, 4, Math.floor(new Date(r.mtime || Date.now()) / 1e3)), n) for (e[3] = 8, r = 0; r <= n.length; ++r) e[r + 10] = n.charCodeAt(r);
        return gn(e, c - 8, a.d()), gn(e, c - 4, t), e;
}
gn = function (e, n, a) {
                for (; a; ++n) e[n] = a, a >>>= 8;
        },
function J(e) {
        function n() {
                for (var e, n = ["xxxxxxxxxxxxxxxxxxxxxxxxxx", "xxxxxxxxxxxxxxxxxxxxxxxxxx"], a = [], c = 0; c < n["length"]; c++) {
                        e = "";
 
                        for (var r = n[c], f = r["length"], o = parseInt("0x" + r["substr"](0, 2)), d = 2; d < f; d += 2) {
                                var i = parseInt("0x" + r["charAt"](d) + r["charAt"](d + 1));
                                e += String["fromCharCode"](i ^ o);
                        }
 
                        a["push"](e);
                }
 
                return a;
        }
 
        var a = ke["codec"]["utf8String"]["toBits"](n()[0]),
                c = ke["codec"]["utf8String"]["toBits"](n()[1]);
        return a = new ke["cipher"]["aes"](a), e = ke["mode"]["cbc"]["encrypt"](a, e, c), ke["codec"]["base64"]["fromBits"](e);
}

2. a2-a8加密前的准备工作.

2.1 a5, a4的加密逻辑(包含两段简单的jsvmp代码, 相对于mtgsig1.1的jsvmp代码, 服主很可能还在练手).

代码中调用的函数也都是简单的运算操作. 例: 

Qn = function () {
        for (var n, a, c = 256, r = []; c--; r[c] = n >>> 0) for (a = 8, n = c; a--;) n = 1 & n ? n >>> 1 ^ 3988292384 : n >>> 1;
 
        return function (n) {
                if ("string" == e(n)) {
                        for (var a = 0, c = -1; a < n["length"]; ++a) c = r[255 & c ^ n["charCodeAt"](a)] ^ c >>> 8;
 
                        return 306674911 ^ c;
                }
 
                for (a = 0, c = -1; a < n["length"]; ++a) c = r[255 & c ^ n[a]] ^ c >>> 8;
 
                return 306674911 ^ c;
        };
}();
function Z(e) {
        var n = [];
        return n[0] = e >>> 24 & 255, n[1] = e >>> 16 & 255, n[2] = e >>> 8 & 255, n[3] = 255 & e, n;
}
function X(e) {
        for (var n = [], a = 0; a < e["length"]; a += 2) {
                var c = e["charAt"](a) + e["charAt"](a + 1);
                c = parseInt(c, 16), n["push"](c);
        }
 
        return n;
}
function W(e) {
        e = encodeURIComponent(e);
 
        for (var n = [], a = 0; a < e["length"]; a++) {
                var c = e["charAt"](a);
                "%" === c ? (c = e["charAt"](a + 1) + e["charAt"](a + 2), c = parseInt(c, 16), n["push"](c), a += 2) : n["push"](c["charCodeAt"](0));
        }
 
        return n;
}
function ae(e, n) {
        var a = e["length"];
        n ^= a;
 
        for (var c = 0; 4 <= a;) {
                var r = 1540483477 * (65535 & (r = 255 & e[c] | (255 & e[++c]) << 8 | (255 & e[++c]) << 16 | (255 & e[++c]) << 24)) + ((1540483477 * (r >>> 16) & 65535) << 16);
                n = 1540483477 * (65535 & n) + ((1540483477 * (n >>> 16) & 65535) << 16) ^ (r = 1540483477 * (65535 & (r ^= r >>> 24)) + ((1540483477 * (r >>> 16) & 65535) << 16)), a -= 4, ++c;
        }
 
        switch (a) {
                case 3:
                        n ^= (255 & e[c + 2]) << 16;
 
                case 2:
                        n ^= (255 & e[c + 1]) << 8;
 
                case 1:
                        n = 1540483477 * (65535 & (n ^= 255 & e[c])) + ((1540483477 * (n >>> 16) & 65535) << 16);
        }
 
        return ((n = 1540483477 * (65535 & (n ^= n >>> 13)) + ((1540483477 * (n >>> 16) & 65535) << 16)) ^ n >>> 15) >>> 0 ^ 1540483477;
}

2.2 d1, 以及最终mtgsig赋值