Question

它是一个简单的加密，但解密它是另一个故事。我将展示加密代码并解释我从那里观察到的内容。

CRC表

static byte[] CRCTable = new byte[] { 
    0, 0x31, 0x62, 0x53, 0xc4, 0xf5, 0xa6, 0x97, 0xb9, 0x88, 0xdb, 0xea, 0x7d, 0x4c, 0x1f, 0x2e, 
    0x43, 0x72, 0x21, 0x10, 0x87, 0xb6, 0xe5, 0xd4, 250, 0xcb, 0x98, 0xa9, 0x3e, 15, 0x5c, 0x6d, 
    0x86, 0xb7, 0xe4, 0xd5, 0x42, 0x73, 0x20, 0x11, 0x3f, 14, 0x5d, 0x6c, 0xfb, 0xca, 0x99, 0xa8, 
    0xc5, 0xf4, 0xa7, 150, 1, 0x30, 0x63, 0x52, 0x7c, 0x4d, 30, 0x2f, 0xb8, 0x89, 0xda, 0xeb, 
    0x3d, 12, 0x5f, 110, 0xf9, 200, 0x9b, 170, 0x84, 0xb5, 230, 0xd7, 0x40, 0x71, 0x22, 0x13, 
    0x7e, 0x4f, 0x1c, 0x2d, 0xba, 0x8b, 0xd8, 0xe9, 0xc7, 0xf6, 0xa5, 0x94, 3, 50, 0x61, 80, 
    0xbb, 0x8a, 0xd9, 0xe8, 0x7f, 0x4e, 0x1d, 0x2c, 2, 0x33, 0x60, 0x51, 0xc6, 0xf7, 0xa4, 0x95, 
    0xf8, 0xc9, 0x9a, 0xab, 60, 13, 0x5e, 0x6f, 0x41, 0x70, 0x23, 0x12, 0x85, 180, 0xe7, 0xd6, 
    0x7a, 0x4b, 0x18, 0x29, 190, 0x8f, 220, 0xed, 0xc3, 0xf2, 0xa1, 0x90, 7, 0x36, 0x65, 0x54, 
    0x39, 8, 0x5b, 0x6a, 0xfd, 0xcc, 0x9f, 0xae, 0x80, 0xb1, 0xe2, 0xd3, 0x44, 0x75, 0x26, 0x17, 
    0xfc, 0xcd, 0x9e, 0xaf, 0x38, 9, 90, 0x6b, 0x45, 0x74, 0x27, 0x16, 0x81, 0xb0, 0xe3, 210, 
    0xbf, 0x8e, 0xdd, 0xec, 0x7b, 0x4a, 0x19, 40, 6, 0x37, 100, 0x55, 0xc2, 0xf3, 160, 0x91, 
    0x47, 0x76, 0x25, 20, 0x83, 0xb2, 0xe1, 0xd0, 0xfe, 0xcf, 0x9c, 0xad, 0x3a, 11, 0x58, 0x69, 
    4, 0x35, 0x66, 0x57, 0xc0, 0xf1, 0xa2, 0x93, 0xbd, 140, 0xdf, 0xee, 0x79, 0x48, 0x1b, 0x2a, 
    0xc1, 240, 0xa3, 0x92, 5, 0x34, 0x67, 0x56, 120, 0x49, 0x1a, 0x2b, 0xbc, 0x8d, 0xde, 0xef, 
    130, 0xb3, 0xe0, 0xd1, 70, 0x77, 0x24, 0x15, 0x3b, 10, 0x59, 0x68, 0xff, 0xce, 0x9d, 0xac
 };

功能

private void CodingToFile()
{
byte[] bytes;
this.DataCorrector(DateTime.Now);
string path = Environment.CurrentDirectory + "\\" + this.newCorrectedData;
byte index = 0;
int num2 = 0;
for (int i = 0; i < this.dataComming.Length; i++)
{
    num2 = this.dataComming[i] + CRCTable[index];
    bytes = BitConverter.GetBytes(num2);
    this.dataComming[i] = bytes[0];
    index = (byte) (index + 1);
}
for (int j = 0; j < this.DeviceIDCode.Length; j++)
{
    num2 = CRCTable[this.DeviceIDCode[j]];
    bytes = BitConverter.GetBytes(num2);
    this.DeviceIDCode[j] = bytes[0];
}
try
{
    if (File.Exists(path))
    {
        File.Delete(path);
    }
    using (FileStream stream = File.Create(path))
    {
        stream.Write(new byte[] { 0x2e, 0x66 }, 0, 2);
        stream.Write(this.DeviceIDCode, 0, 7);
        stream.Write(this.dataComming, 0, this.dataComming.Length);
        stream.Close();
    }
}
catch
{
}
this.flagAutomaticIDIsOK = false;

}

因此文件的前2个字节并不是那么重要，接下来的7个字节只是DeviceID，我对 dataComming 部分更感兴趣。

byte index = 0;
int num2 = 0;
for (int i = 0; i < this.dataComming.Length; i++)
{
    num2 = this.dataComming[i] + CRCTable[index];
    bytes = BitConverter.GetBytes(num2);
    this.dataComming[i] = bytes[0];
    index = (byte) (index + 1);
}

fyi this.dataComming 被声明为字节

所以num2被赋值为 this.dataComming [i] + CRCTable [index] ，这可能是超过255（一个字节的最大大小）但可能低于511的值。

num2被包含在字节中（int的大小为4个字节）

this.dataComming [i] = bytes [0] - 但我们只读取4个字节中的1个（但如果我的理论正确，则只有2个应该被占用）

所以我想要反转这个并抓取数据，我不知道任何.NET，所以我尝试用像PHP这样简单的东西来做，但结果却是乱七八糟的。这是我到目前为止所得到的

PHP `

$f = fopen("0208215642", "rb");

 $CRCTable = array( 
    0, 0x31, 0x62, 0x53, 0xc4, 0xf5, 0xa6, 0x97, 0xb9, 0x88, 0xdb, 0xea, 0x7d, 0x4c, 0x1f, 0x2e, 
    0x43, 0x72, 0x21, 0x10, 0x87, 0xb6, 0xe5, 0xd4, 250, 0xcb, 0x98, 0xa9, 0x3e, 15, 0x5c, 0x6d, 
    0x86, 0xb7, 0xe4, 0xd5, 0x42, 0x73, 0x20, 0x11, 0x3f, 14, 0x5d, 0x6c, 0xfb, 0xca, 0x99, 0xa8, 
    0xc5, 0xf4, 0xa7, 150, 1, 0x30, 0x63, 0x52, 0x7c, 0x4d, 30, 0x2f, 0xb8, 0x89, 0xda, 0xeb, 
    0x3d, 12, 0x5f, 110, 0xf9, 200, 0x9b, 170, 0x84, 0xb5, 230, 0xd7, 0x40, 0x71, 0x22, 0x13, 
    0x7e, 0x4f, 0x1c, 0x2d, 0xba, 0x8b, 0xd8, 0xe9, 0xc7, 0xf6, 0xa5, 0x94, 3, 50, 0x61, 80, 
    0xbb, 0x8a, 0xd9, 0xe8, 0x7f, 0x4e, 0x1d, 0x2c, 2, 0x33, 0x60, 0x51, 0xc6, 0xf7, 0xa4, 0x95, 
    0xf8, 0xc9, 0x9a, 0xab, 60, 13, 0x5e, 0x6f, 0x41, 0x70, 0x23, 0x12, 0x85, 180, 0xe7, 0xd6, 
    0x7a, 0x4b, 0x18, 0x29, 190, 0x8f, 220, 0xed, 0xc3, 0xf2, 0xa1, 0x90, 7, 0x36, 0x65, 0x54, 
    0x39, 8, 0x5b, 0x6a, 0xfd, 0xcc, 0x9f, 0xae, 0x80, 0xb1, 0xe2, 0xd3, 0x44, 0x75, 0x26, 0x17, 
    0xfc, 0xcd, 0x9e, 0xaf, 0x38, 9, 90, 0x6b, 0x45, 0x74, 0x27, 0x16, 0x81, 0xb0, 0xe3, 210, 
    0xbf, 0x8e, 0xdd, 0xec, 0x7b, 0x4a, 0x19, 40, 6, 0x37, 100, 0x55, 0xc2, 0xf3, 160, 0x91, 
    0x47, 0x76, 0x25, 20, 0x83, 0xb2, 0xe1, 0xd0, 0xfe, 0xcf, 0x9c, 0xad, 0x3a, 11, 0x58, 0x69, 
    4, 0x35, 0x66, 0x57, 0xc0, 0xf1, 0xa2, 0x93, 0xbd, 140, 0xdf, 0xee, 0x79, 0x48, 0x1b, 0x2a, 
    0xc1, 240, 0xa3, 0x92, 5, 0x34, 0x67, 0x56, 120, 0x49, 0x1a, 0x2b, 0xbc, 0x8d, 0xde, 0xef, 
    130, 0xb3, 0xe0, 0xd1, 70, 0x77, 0x24, 0x15, 0x3b, 10, 0x59, 0x68, 0xff, 0xce, 0x9d, 0xac
 );



fread($f, 9); //first 9 bytes are just program related information.


$index = 0;

while(!feof($f)) {
    $baseValue =  ord(fread($f,1)); //grab the ASCII value of the character.

    $baseValue = abs($baseValue - intval($CRCTable[$index]));       
    echo chr($baseValue);
    $index++;
    if($index == count($CRCTable)) $index = 0; //we've reached the end of the CRCTable array.
}
fclose($f);
return;
?>

` 但我想我在 $ baseValue = ... 部分遗漏了一些内容，如何弥补.NET CodingToFile（）函数丢失的字节。

如果这令人困惑，我很抱歉！我尽力解释它，

Anyhelp将不胜感激（实际上你对我来说意味着世界：D）

干杯！

Answer 1

这是一个Caesar密码，带有256个元素的密钥。

加密代码可以简化如下：

for (int i = 0; i < dataComming.Length; i++) {
    dataComming[i] += CRCTable[i & 0xFF];
}

这使逆转显而易见：

for (int i = 0; i < dataComming.Length; i++) {
    dataComming[i] -= CRCTable[i & 0xFF];
}

我不知道为什么使用CRC表作为密钥，因此制定一个好的加密密钥会有太多的规律性。当然，对于这种弱的算法，关键可能并不重要。

需要帮助扭转简单加密

1 个答案: