Analysis of an e-commerce App sign signature algorithm (5)

1. Goals

Boss Li: Fenfei, it is said that an e-commerce app has been upgraded and a 64-bit sign has been created. What's even better is that all the entries are encrypted!

Fenfei: It's so cool, pull it out and let's play.

v10.3.2

Two, steps

32-bit and 64-bit

We have mastered so many methods, how about searching for strings first? Or Hook first?

Zi once said: When you see a 32-bit signature, you think of MD5 and HmacSHA1, and when you see a 64-bit signature, you think of HmacSHA256.

Then first engage in java cryptography-related functions:

var secretKeySpec = Java.use('javax.crypto.spec.SecretKeySpec');
secretKeySpec.$init.overload('[B','java.lang.String').implementation = function (a,b) {
	var result = this.$init(a, b);
    console.log(">>> 算法名" + b);
    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("mac ======================================");
    console.log("算法名：" + a);
    return result;
}

mac.doFinal.overload('[B').implementation = function (a) {
    // showStacks();
    var result = this.doFinal(a);
    console.log("mac ======================================");
    console.log("doFinal参数:" + bytesToString(a));
    console.log("doFinal结果(hex):" + bytesToHex(result));
    console.log("doFinal结果(base):" + bytesToBase64(result));

    // var stack = threadinstance.currentThread().getStackTrace();
    // console.log("Full call stack:" + Where(stack));

    return result;
}
// */

run.

TIP: Remember to refer to the previous article http://91fans.com.cn/post/ldqsignone/ to change the frida port number

Fortunately, it really is.

What is the key?

The difference between HmacSHA256 and md5 is that it passes a key. We try to find out this key.

first print the stack

Full call stack:dalvik.system.VMStack.getThreadStackTrace(Native Method)
java.lang.Thread.getStackTrace(Thread.java:1720)
javax.crypto.Mac.doFinal(Native Method)
com.jxxxxong.sdk.xxcrashreport.a.z.a(XXCrashReportFile:63)
com.jxxxxong.sdk.xxcrashreport.a.z.a(XXCrashReportFile:136)
com.jxxxxong.sdk.xxcrashreport.a.o.Ve(XXCrashReportFile:154)
com.jxxxxong.sdk.xxcrashreport.a.o.<init>(XXCrashReportFile:135)
com.jxxxxong.sdk.xxcrashreport.a.o.<init>(XXCrashReportFile:37)
com.jxxxxong.sdk.xxcrashreport.a.o$a.Vf(XXCrashReportFile:245)
com.jxxxxong.sdk.xxcrashreport.a.ai$a.run(XXCrashReportFile:133)

Originally, I wanted to find out the key directly from the static code, but I was dizzy after going around.

Forget it, add a Hook.

var getKeyCls = Java.use("com.jxxxxong.sdk.xxcrashreport.a.z");
getKeyCls.a.overload('[B', '[B').implementation = function(a,b){
        var result = this.a(a,b);

        var StrCls = Java.use('java.lang.String');
        var keyStr = StrCls.$new(b);
        var dataStr = StrCls.$new(a);

        console.log(">>> dataStr=" + dataStr);
        console.log(">>> key=" + keyStr);
        console.log(">>> rc=" + result);
        return result;
}

keep running down

check

The plaintext is there, the key is there, and the result is also there. We can check it out.

def main():
    data = "yingyan&R4iSKKKKKKKKKK3Ckm6NCKyP4XpntPMcsmTiVIdoeOlPYBLNS1PK0O4e747X79c5P3zFQbh3LbJlFUCRaaIQTPKmipOYkJUu6OAqZT1xx6MMacwy/v5yxRvbdYAwdhXVCF7zmi+DHbQ16PPDpn/R9PPnPifGbirJeG9yKKKK&R4iSKKKKKKKKKBC0CtGnLKMgYWz/LGKKKK==&android&10.3.2&R4iSKKKKKKKKKOlFz0/FIGUKUpUcZGYKKKK=&R4iSKKKKKKKKKKlShOtDUJLIsFKLKA589d0AKKKK&uvReport&R4iSKKKKKKKKKNC0KKNrTV2rKqKKKK==&huawei&R4iSKKKKKKKKKNC0CJRGCtS3DKSK/BvloKuKKKK=&E1.1&1641614274084&R4iSKKKKKKKKKNDBjBK0JNG1DurECbE0iBGOKNhLaV4GKKKK".encode('utf-8')

    # 890394FD47EB218CADB73B3FFF976CFE571AC255E1BD5F7AFE427CED13B52DBC
    signature = hmac.new(appsecret, data, digestmod=sha256).hexdigest().upper()
    print(signature)

Life is short, use Python quickly

Call it a day~ Let's take a break, let's do the encryption tomorrow.

3. Summary

Grabbed the package again and compared it. The signature in the &sign=xxx&sv=xxx mode still exists, and the algorithm with a high probability has not changed.

The previous version of 64-bit sign also exists, and the probability has not changed.

So, the boss is always right .

Dig down from where you stand, and you will surely find a clear spring.