Vb.net算术运算导致解码溢出 [英] Vb.net arithmetic operation resulted in an overflow in decoding

问题描述

我正在为密码恢复工具开发新的解码功能。我尝试用c ++编写代码并且工作（我没有写这个函数）：

  void  poco_pwd（u_char * pwd， int  type）{
  int  len， 
 tmp; 
 u_char * out; 
 简短 azz; 
 
  if （type）azz = 0x2537;  //  加密邮件 
  else  azz = 0x2a9a;  //  其他密码 
 
 len = strlen（pwd）>>  1 ; 
  out  = pwd; 
  while （len--）{
 sscanf（pwd， ％02X，& tmp）; 
 pwd + =  2 ; 
 * out ++ = tmp ^（azz>>  8 ）; 
 azz =（（tmp + azz）* 0x8141）+ 0x3171; 
} 
 * out =  0 ; 
} 

我试图将此代码转换为vb.net和c＃但它抛出算术溢出操作。此函数的新值被赋予azz变量。 azz是一个短变量，但这些值非常长（（（tmp + azz）* 0x8141）+ 0x3171）。奇怪的是它适用于c ++。



我尝试过的事情：



我将此代码转换为vb.net：

  Dim  encpass 作为 字符串 =  < span class =code-string> 1EF66D8BD3C32476CEC8CF '  Hex值 
  Dim  encpassByte 作为 字节（）=编码.UTF8.GetBytes（HexToString（encpass））
  Dim  azz  As  整数 =& H2A9A 
  Dim  len  As  < span class =code-keyword>整数 = encpassByte.Length>>  1  
  Dim  storage（len） As  字符 
 
 对于 i =  0    len 
 storage（i）=（ChrW（encpassByte（i） Xor （azz>>  8 ）））
 azz =（（encpassByte（i）+ azz）*& H8141）+ & H3171 ' 错误：算术运算导致溢出。 
 下一步 
 
 Console.WriteLine（storage.ToString）
 Console.ReadKey（）

十六进制到字符串函数

 函数 HexToString（ ByVal  hex  As   String ） 作为 字符串 
  Dim 文字 As  新 System.Text.StringBuilder（hex.Length \  2 ）
 对于 i 作为 整数 =  0    hex.Length  -   2  步骤  2  
 text.Append（Chr（Convert.ToByte） （hex.Substring（i， 2 ）， 16 ）））
 下一步 
 返回 text.ToString 
 结束 功能 

解决方案

整数有32位。如果数字大于那个，你可能会得到ArithmeticOverflow异常。旧的C ++并不关心：它只是丢掉了第33个字节及以上的值。这意味着你需要在某种程度上模拟C ++的脏行为。使用C＃，您可以使用未选中关键字，但VB.Net中似乎没有等效项。

也就是说，我没有看到VB.Net标准功能的解决方案。我会寻找一个64位整数类型的库，使用该类型的临时变量进行计算，然后按按位和将其恢复为32位。 / BLOCKQUOTE>

I am working on new decode function for password recovery tool. I tried code in c++ and worked (i did not write this function):

void poco_pwd(u_char *pwd, int type) {
    int     len,
            tmp;
    u_char  *out;
    short   azz;

    if(type) azz = 0x2537;  // encrypt message
        else azz = 0x2a9a;  // other passwords

    len = strlen(pwd) >> 1;
    out = pwd;
    while(len--) {
        sscanf(pwd, "%02X", &tmp);
        pwd += 2;
        *out++ = tmp ^ (azz >> 8);
        azz = ((tmp + azz) * 0x8141) + 0x3171;
    }
    *out = 0;
}

I tried to convert this code to vb.net and c# but it throws arithmetic overflow operation. This function new value is put to "azz" variable. "azz" is a short variable but this these values are very long (((tmp + azz) * 0x8141) + 0x3171). Strange is that it works in c++.

What I have tried:

I converted this code to vb.net:

Dim encpass As String = "1EF66D8BD3C32476CEC8CF" 'Hex Value
Dim encpassByte As Byte() = Encoding.UTF8.GetBytes(HexToString(encpass))
Dim azz As Integer = &H2A9A
Dim len As Integer = encpassByte.Length >> 1
Dim storage(len) As Char

For i = 0 To len
    storage(i) = (ChrW(encpassByte(i) Xor (azz >> 8)))
    azz = ((encpassByte(i) + azz) * &H8141) + &H3171 'Error: arithmetic operation resulted in an overflow.
Next

Console.WriteLine(storage.ToString)
Console.ReadKey()

Hex to string function

Function HexToString(ByVal hex As String) As String
    Dim text As New System.Text.StringBuilder(hex.Length \ 2)
    For i As Integer = 0 To hex.Length - 2 Step 2
        text.Append(Chr(Convert.ToByte(hex.Substring(i, 2), 16)))
    Next
    Return text.ToString
End Function

解决方案

An Integer has 32 bits. If the number gets bigger than that, you may get that ArithmeticOverflow exception. Old C++ didn't care: it just threw away the value of the 33rd byte and beyond. That means you need here some way to simulate that dirty behavior of C++. With C#, you can use the unchecked keyword, but there seems to be no equivalent in VB.Net.
That said, I don't see a solution with VB.Net's standard functionality. I'd look for a library with a 64bit integer type, doing the calculation with a temporary variable of that type, then do a bitwise and to get it back to 32bits.

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