一次简单算法还原的感触
本帖最后由 mmmmar 于 2016-6-12 19:40 编辑刚才就发了个帖子求一个助软件注册算法还原的帖子。结果好多都一眼看出来是计算机二级C语言掌上通的，本来上午写了个破解它的详细过程的帖子，突发奇想想加一个算法还原的方法，结果一弄弄了一下午。
中间一手残把浏览器给关了。。。打开一看虽然有还原功能但是插的图片都没了。刚才搜了下论坛有这方面的帖子，所以详细的教程就不发了，只说一下算法还原的方面。
刚刚知道自己哪出错了，忘了类型转换把byte类型的值加了255，我说结果的16进制里全是FF
计算机二级C语言掌上通注册码生成过程如下，位于Lcom/xqh/cexam/cc;的onPayFinish()方法中
iget-object v0, p0, Lcom/xqh/cexam/bf;->a:Lcom/xqh/cexam/MainActivity;
invoke-virtual {v0}, Lcom/xqh/cexam/MainActivity;->i()Ljava/lang/String;
move-result-object v0
invoke-static {v0}, Lcom/xqh/cexam/cq;->b(Ljava/lang/String;)Ljava/lang/String;
move-result-object v0
iget-object v1, p0, Lcom/xqh/cexam/bf;->a:Lcom/xqh/cexam/MainActivity;
iget-object v1, v1, Lcom/xqh/cexam/MainActivity;->u:Landroid/widget/EditText;
invoke-virtual {v1, v0}, Landroid/widget/EditText;->setText(Ljava/lang/CharSequence;)V
可以看到，先调用MainActivity的i()，然后把返回结果当作参数传递给Lcom/xqh/cexam/cq的b()方法，b()方法的返回值就是注册码
先看MainActivity的i()方法
.method public i()Ljava/lang/String;
.locals 3
:try_start_0
const-string v0, "phone"
invoke-virtual {p0, v0}, Lcom/xqh/cexam/MainActivity;->getSystemService(Ljava/lang/String;)Ljava/lang/Object;
move-result-object v0
check-cast v0, Landroid/telephony/TelephonyManager;
new-instance v1, Ljava/lang/StringBuilder;
const-string v2, "L"
invoke-direct {v1, v2}, Ljava/lang/StringBuilder;-><init>(Ljava/lang/String;)V
invoke-virtual {v0}, Landroid/telephony/TelephonyManager;->getDeviceId()Ljava/lang/String;
move-result-object v0
invoke-virtual {v0}, Ljava/lang/String;->toUpperCase()Ljava/lang/String;
move-result-object v0
invoke-virtual {v1, v0}, Ljava/lang/StringBuilder;->append(Ljava/lang/String;)Ljava/lang/StringBuilder;
move-result-object v0
const-string v1, "8H6"
invoke-virtual {v0, v1}, Ljava/lang/StringBuilder;->append(Ljava/lang/String;)Ljava/lang/StringBuilder;
move-result-object v0
invoke-virtual {v0}, Ljava/lang/StringBuilder;->toString()Ljava/lang/String;
:try_end_0
.catch Ljava/lang/Exception; {:try_start_0 .. :try_end_0} :catch_0
move-result-object v0
const/4 v1, 0x1
invoke-static {p0, v0, v1}, Landroid/widget/Toast;->makeText(Landroid/content/Context;Ljava/lang/CharSequence;I)Landroid/widget/Toast;
move-result-object v2
invoke-virtual {v2}, Landroid/widget/Toast;->show()V
:goto_0
return-object v0
:catch_0
move-exception v0
const-string v0, "TH1109ZXN0914"
invoke-virtual {v0}, Ljava/lang/String;->toUpperCase()Ljava/lang/String;
move-result-object v0
goto :goto_0
.end method
这段代码很简单，就在获取的DeviceID前后加了两个字符串
核心的简单算法,位于Lcom/xqh/cexam/cq
.method public static b(Ljava/lang/String;)Ljava/lang/String;
.locals 5
#获取md5实例
:try_start_0
const-string v0, "MD5"
invoke-static {v0}, Ljava/security/MessageDigest;->getInstance(Ljava/lang/String;)Ljava/security/MessageDigest;
move-result-object v0
new-instance v1, Ljava/lang/StringBuilder;
const-string v2, "niat.xqh"
invoke-direct {v1, v2}, Ljava/lang/StringBuilder;-><init>(Ljava/lang/String;)V
invoke-virtual {v1, p0}, Ljava/lang/StringBuilder;->append(Ljava/lang/String;)Ljava/lang/StringBuilder;
move-result-object v1
const-string v2, "c2exam86"
invoke-virtual {v1, v2}, Ljava/lang/StringBuilder;->append(Ljava/lang/String;)Ljava/lang/StringBuilder;
move-result-object v1
invoke-virtual {v1}, Ljava/lang/StringBuilder;->toString()Ljava/lang/String;
move-result-object v1
#加密后的字节数组
invoke-virtual {v1}, Ljava/lang/String;->getBytes()[B
move-result-object v1
invoke-virtual {v0, v1}, Ljava/security/MessageDigest;->update([B)V
invoke-virtual {v0}, Ljava/security/MessageDigest;->digest()[B
move-result-object v2
new-instance v3, Ljava/lang/StringBuffer;
const-string v0, ""
invoke-direct {v3, v0}, Ljava/lang/StringBuffer;-><init>(Ljava/lang/String;)V
const/4 v0, 0x0
move v1, v0
:goto_0
array-length v0, v2
if-lt v1, v0, :cond_0
invoke-virtual {v3}, Ljava/lang/StringBuffer;->toString()Ljava/lang/String;
move-result-object v0
const/4 v1, 0x4
const/16 v2, 0x17
invoke-virtual {v0, v1, v2}, Ljava/lang/String;->substring(II)Ljava/lang/String;
move-result-object v0
invoke-virtual {v0}, Ljava/lang/String;->toUpperCase()Ljava/lang/String;
move-result-object v0
return-object v0
:cond_0
aget-byte v0, v2, v1
if-gez v0, :cond_1
#注意这里！！！！！！！！！！ 把v0转换成了int型
add-int/lit16 v0, v0, 0x100
:cond_1
const/16 v4, 0x10
if-ge v0, v4, :cond_2
const-string v4, "0"
invoke-virtual {v3, v4}, Ljava/lang/StringBuffer;->append(Ljava/lang/String;)Ljava/lang/StringBuffer;
:cond_2
invoke-static {v0}, Ljava/lang/Integer;->toHexString(I)Ljava/lang/String;
move-result-object v0
invoke-virtual {v3, v0}, Ljava/lang/StringBuffer;->append(Ljava/lang/String;)Ljava/lang/StringBuffer;
:try_end_0
.catch Ljava/security/NoSuchAlgorithmException; {:try_start_0 .. :try_end_0} :catch_0
add-int/lit8 v0, v1, 0x1
move v1, v0
goto :goto_0
:goto_1
const-string v1, "TH1109ZXN0914"
invoke-virtual {v0}, Ljava/security/NoSuchAlgorithmException;->printStackTrace()V
goto :goto_1
:catch_0
move-exception v0
goto :goto_1
.end method
还原之后代码为：
public String b(String param){
try {
MessageDigest messageDigest = MessageDigest.getInstance("MD5");
String str = "niat.xqh"+param+"c2exam86";
messageDigest.update(str.getBytes());
byte[] result = messageDigest.digest();
StringBuilder builder = new StringBuilder();
int i= 0;
while(i<result.length){
//刚开始写成了byte型，结果一直不对
int v =result;
if(v<0){
v+=256;
}
if(v<16){
builder.append("0");
}
builder.append(Integer.toHexString(v));
i++;
}
String v3 = builder.toString();
v3 = v3.substring(4,23);
return v3.toUpperCase();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
return "";
}
smali码和java对比着看就很容易看懂了，折腾了整整一下午，去动态调试也没看出来什么，结果是变量类型的原因。
详细教程点这里！！！！！！
最后吐槽一下，这软件解锁之后的编程功能竟然是给装个C4droid，太无耻了吧
真不错～哈哈 来学习学习 66666666学习一下把
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