解密加密文件时出现 C#“Bad Data”异常

Question

嘿，我对加密和解密非常陌生，老实说，甚至是 c# 语言。基本上，我有一个 tcp 聊天服务器，可以“保存”日志并加密文本文件。这就是我加密的方式（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 = 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();
}

当我检查加密流对象时，它说它抛出了一个异常，“流不支持搜索”。

任何帮助将不胜感激！

Answer 1

这里：

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

您将直接关闭fsOut，而不关闭cryptostream。这意味着加密流没有机会刷新任何最终块等。

另外：

• 使用 using 语句而不是手动调用 Close 或 Dispose
• 您当前调用Read 一次，并假设它会读取所有数据 - 您没有检查返回值。 （由于某种原因，您还删除了输入文件的最后一个字节......为什么？）通常，您应该循环，读入缓冲区，然后写出您读取的字节数，直到 Read 方法返回 0 . 如果您使用 .NET 4，Stream.CopyTo 是您的朋友。

Answer 2

  objCryptStream.CopyTo(stream);

为我工作，完整的代码是

 public static string DecryptString(string encriptedText, string key)
   {

       try
       {


           //Convert the text into bytest
           byte[] ecriptedBytes = System.Convert.FromBase64String(encriptedText);

           // Create a memory stream to the passed buffer
           MemoryStream objMemStream = new MemoryStream(ecriptedBytes);

           //Set the legal keys and initialization verctors
           objCrptoService.Key = GetLegalsecretKey(key);
           objCrptoService.IV = GetLegalIV();

           // Create a CryptoStream using the memory stream and the cryptographic service provider  version
           // of the Data Encryption stanadard algorithm key
           CryptoStream objCryptStream = new CryptoStream(objMemStream, objCrptoService.CreateDecryptor(), CryptoStreamMode.Read);

           // Create a StreamReader for reading the stream.
           //StreamReader objstreamReader = new StreamReader(objCryptStream);
           MemoryStream stream = new MemoryStream();
           objCryptStream.CopyTo(stream);
           stream.Position = 0;
           StreamReader R = new StreamReader(stream);
           string outputText = R.ReadToEnd();

           // Close the streams.
           R.Close();
           objCryptStream.Close();
           objMemStream.Close();

           return outputText;
       }
       catch (Exception exc)
       {
           return "";
       }
   }

Answer 3

解决我的问题是在创建文件时在加密流上调用 FlushFinalBlock

                CryptoStream cryptostream = new CryptoStream(memoryStream, this._encryptionKeyHelper.Encryptor(), CryptoStreamMode.Write);

            xmlser.Serialize(cryptostream, builderObject);

            cryptostream.FlushFinalBlock();