C＃“坏数据”解密加密文件时出现异常 [英] C# "Bad Data" exception when decrypting encrypted file

问题描述

我非常新加密和解密，甚至c＃语言是诚实的。基本上，我有一个tcp聊天服务器保存日志并加密文本文件。这是我如何加密（基于MSDN示例）：

  public static void EncryptFile（string strInputFileName，string strOutputFileName，string strKey ）
 {
 FileStream fsIn = new FileStream（strInputFileName，FileMode.Open，FileAccess.Read）; 
 FileStream fsOut = new FileStream（strOutputFileName，FileMode.Create，FileAccess.Write）; 
 
 DESCryptoServiceProvider des = new DESCryptoServiceProvider（）; 
 des.Key = ASCIIEncoding.ASCII.GetBytes（strKey）; 
 des.IV = ASCIIEncoding.ASCII.GetBytes（strKey）; 
 
 
 ICryptoTransform desencrypt = des.CreateEncryptor（）; 
 CryptoStream cryptostream = new CryptoStream（fsOut，desencrypt，CryptoStreamMode.Write）; 
 
 byte [] byteArrayInput = new byte [fsIn.Length  -  1]; 
 fsIn.Read（byteArrayInput，0，byteArrayInput.Length）; 
 cryptostream.Write（byteArrayInput，0，byteArrayInput.Length）; 
 
 fsIn.Close（）; 
 fsOut.Close（）; 
} 
  

方法成功完全加密文件。这是我的解密方法：

  public static void DecryptFile（string strInputFileName，string strOutputFileName，string strKey）
 {
 DESCryptoServiceProvider des = new DESCryptoServiceProvider（）; 
 des.Key = ASCIIEncoding.ASCII.GetBytes（strKey）; 
 des.IV = ASCIIEncoding.ASCII.GetBytes（strKey）; 
 
 byte [] te =新字节[1024]; 
 FileStream fsRead = new FileStream（strInputFileName，FileMode.Open，FileAccess.Read）; 
 ICryptoTransform desdecrypt = des.CreateDecryptor（）; 
 
 CryptoStream cryptostream = new CryptoStream（fsRead，desdecrypt，CryptoStreamMode.Read）; 
 StreamWriter fsDecrypted = new StreamWriter（strOutputFileName）; 
 
 fsDecrypted.Write（new StreamReader（cryptostream）.ReadToEnd（））; //这是坏数据发生的地方。 
 fsDecrypted.Flush（）; 
 fsDecrypted.Close（）; 
 fsRead.Close（）; 
} 
  

当我检查cryptostream对象时，它表示已经抛出异常，Stream不支持搜索。

任何帮助将不胜感激！

解决方案

这里：

  cryptostream.Write（byteArrayInput，0，byteArrayInput.Length）; 
 fsIn.Close（）; 
 fsOut.Close（）; 
  

直接关闭 fsOut 关闭 cryptostream 。这意味着加密流没有机会刷新任何最终的块等。

另外：

• 使用语句，而不是手动调用Close或Dispose


• 您正在调用读取一次，假设它将读取所有数据 - 您不会检查返回值。 （你也在删除输入文件的最后一个字节，为什么？）一般来说，你应该循环，读入缓冲区，然后写出你读取的很多字节，直到Read方法返回0 。如果您使用的是.NET 4， Stream.CopyTo 是您的朋友。

Hey I'm very new to encryption and decryption, or even the c# language to be honest. Basically, I have a tcp chat server that "saves" logs and encrypts the text file. This is how I encrypt (based from the MSDN sample):

public static void EncryptFile(string strInputFileName, string strOutputFileName, string strKey)
{
    FileStream fsIn = new FileStream(strInputFileName, FileMode.Open, FileAccess.Read);
    FileStream fsOut = new FileStream(strOutputFileName, FileMode.Create, FileAccess.Write);

    DESCryptoServiceProvider des = new DESCryptoServiceProvider();
    des.Key = ASCIIEncoding.ASCII.GetBytes(strKey);
    des.IV = ASCIIEncoding.ASCII.GetBytes(strKey);


    ICryptoTransform desencrypt = des.CreateEncryptor();
    CryptoStream cryptostream = new CryptoStream(fsOut, desencrypt, CryptoStreamMode.Write);

    byte[] byteArrayInput = new byte[fsIn.Length - 1];
    fsIn.Read(byteArrayInput, 0, byteArrayInput.Length);
    cryptostream.Write(byteArrayInput, 0, byteArrayInput.Length);

    fsIn.Close();
    fsOut.Close();
}

The method success fully encrypts files. This is my decrypt method:

public static void DecryptFile(string strInputFileName, string strOutputFileName, string strKey)
{
    DESCryptoServiceProvider des = new DESCryptoServiceProvider();
    des.Key = ASCIIEncoding.ASCII.GetBytes(strKey);
    des.IV = ASCIIEncoding.ASCII.GetBytes(strKey);

    byte[] te = new byte[1024];
    FileStream fsRead = new FileStream(strInputFileName, FileMode.Open, FileAccess.Read);
    ICryptoTransform desdecrypt = des.CreateDecryptor();          

    CryptoStream cryptostream = new CryptoStream(fsRead, desdecrypt, CryptoStreamMode.Read);
    StreamWriter fsDecrypted = new StreamWriter(strOutputFileName);            

    fsDecrypted.Write(new StreamReader(cryptostream).ReadToEnd());//This is where the "Bad Data" occurs.
    fsDecrypted.Flush();
    fsDecrypted.Close();
    fsRead.Close();
}

And when I inspect the cryptostream object, it says that it has thrown an exception, "Stream does not support seeking".

Any help would be greatly appreciated!

解决方案

Here:

    cryptostream.Write(byteArrayInput, 0, byteArrayInput.Length);
    fsIn.Close();
    fsOut.Close();

You're closing fsOut directly, without closing cryptostream. That means the crypto stream doesn't get the chance to flush any final blocks etc.

Additionally:

• Use using statements instead of manually calling Close or Dispose
• You're currently calling Read once, and assuming it will read all the data - you're not checking the return value. (You're also removing the last byte of the input file for some reason... why?) In general, you should loop round, reading into a buffer and then writing out however many bytes you read, until the Read method returns 0. If you're using .NET 4, Stream.CopyTo is your friend.

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