【发布时间】：2015-01-16 22:47:52
【问题描述】：
我正在实现文件的加密/解密，其中只应加密一定数量的字节。 例如：我有 500 MB 的大文件，我只想加密（当然还有解密）2 MB 的文件。
我已经实现了一切，加密工作正常（没有错误），但是当我运行解密时它总是抛出这个错误：
System.Security.Cryptography.CryptographicException: Padding is invalid and cannot be removed.
at System.Security.Cryptography.CapiSymmetricAlgorithm.DepadBlock(Byte[] block, Int32 offset, Int32 count) at System.Security.Cryptography.CapiSymmetricAlgorithm.TransformFinalBlock(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount)
at System.Security.Cryptography.CryptoStream.FlushFinalBlock()
at System.Security.Cryptography.CryptoStream.Dispose(Boolean disposing)
at System.IO.Stream.Close()
at System.IO.Stream.Dispose()
at ...
然后我尝试将 Padding 设置为encryptor.Padding = PaddingMode.None;（并且还尝试了 PaddingMode.Zeros 等）。使用这种填充模式运行加密和解密后解密的结果没有错误/异常，但文件的加密部分仍然被加密，但有点不同。我还检查了密码是否正确
现在我没有更多的解决方案来处理这种文件的“部分”加密。有任何想法吗？如何处理这个填充或字节？
这是我的一定数量字节的加密和解密过程的代码（对不起长度，但只有你会知道:)）：
static byte[] FILE_HEADER = Encoding.Default.GetBytes("header_of_file"); //this is written to the first line of encrypted file
static long limitBytes = 4096 * 8; //limit encryption to this amount of bytes
public static bool Encrypt(string inputFilePath, string outputfilePath, string EncryptionKey)
{
int bytesRead = 1;
long byteWriteCounter = 0;
long encryptedByteCounter = 0;
byte[] blength = null;
byte[] intBytes = null;
int bufferLen = 4096;
byte[] buffer = new byte[bufferLen];
blength = new byte[FILE_HEADER.Length];
long sumBytesRead = 0;
try
{
using (FileStream fsInput = new FileStream(inputFilePath, FileMode.Open))
{
fsInput.Read(blength, 0, blength.Length);
if (!blength.SequenceEqual(FILE_HEADER)) //read the FILE_HEADER - if not equal that we can encrypt otherwise is already encrypted
{
fsInput.Position = 0;
using (FileStream fsOutput = new FileStream(outputfilePath, FileMode.Create))
{
using (Aes encryptor = Aes.Create())
{
Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
encryptor.Key = pdb.GetBytes(32);
encryptor.IV = pdb.GetBytes(16);
using (CryptoStream cs = new CryptoStream(fsOutput, encryptor.CreateEncryptor(), CryptoStreamMode.Write))
{
try
{
while (bytesRead != 0)
{
bytesRead = fsInput.Read(buffer, 0, bufferLen);
sumBytesRead += bytesRead;
if (sumBytesRead <= limitBytes) //limit encryption
{
if (bytesRead < bufferLen)
{
cs.Write(buffer, 0, bytesRead);
encryptedByteCounter += bytesRead;
byteWriteCounter += bytesRead;
intBytes = Encoding.Default.GetBytes(encryptedByteCounter.ToString("D7"));
fsOutput.Position = 0;
fsOutput.Write(FILE_HEADER, 0, FILE_HEADER.Length); //we write our header to file, to know which is encrypted
fsOutput.Write(intBytes, 0, intBytes.Length); //we write number of encrypted bytes next to header, for decryption to know
bytesRead = 0;
}
else
{
cs.Write(buffer, 0, bytesRead);
encryptedByteCounter += bytesRead;
byteWriteCounter += bytesRead;
}
}
else //if the file is bigger than limit, we continue to write normal data (unencrypted)
{
if (bytesRead < bufferLen)
{
fsOutput.Write(buffer, 0, bytesRead);
byteWriteCounter += bytesRead;
intBytes = Encoding.Default.GetBytes(encryptedByteCounter.ToString("D7"));
fsOutput.Position = 0;
fsOutput.Write(FILE_HEADER, 0, FILE_HEADER.Length);
fsOutput.Write(intBytes, 0, intBytes.Length);
bytesRead = 0;
}
else
{
fsOutput.Write(buffer, 0, bytesRead);
byteWriteCounter += bytesRead;
}
}
}
}
catch (SystemException se)
{
Console.WriteLine("Exception ENC: " + se);
}
}
}
}
return true;
}
else
{
//file is already encrypted
return false;
}
}
}
catch (SystemException se)
{
Console.WriteLine("Main ENC exception: "+se);
return false;
}
}
...及解密功能：
public static bool Decrypt(string inputFilePath, string outputfilePath, string EncryptionKey)
{
byte[] blength = null;
blength = new byte[FILE_HEADER.Length];
long byteWriteCounter = 0;
int bufferLen = 4096;
byte[] buffer = new byte[bufferLen];
int bytesRead = 1;
long decryptedByteCounter = 0;
long sumBytesRead = 0;
byte[] bufferEncBytes = new byte[7];
try
{
using (FileStream fsInput = new FileStream(inputFilePath, FileMode.Open))
{
fsInput.Read(blength, 0, blength.Length);
if (blength.SequenceEqual(FILE_HEADER))//check if is our encrypted file
{
fsInput.Read(bufferEncBytes, 0, bufferEncBytes.Length);
int numOfDecBytes = Convert.ToInt32(Encoding.Default.GetString(bufferEncBytes)); //get number of encrypted bytes
using (FileStream fsOutput = new FileStream(outputfilePath, FileMode.Create))
{
using (Aes encryptor = Aes.Create())
{
Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
encryptor.Key = pdb.GetBytes(32);
encryptor.IV = pdb.GetBytes(16);
using (CryptoStream cs = new CryptoStream(fsOutput, encryptor.CreateDecryptor(), CryptoStreamMode.Write))
{
try
{
while (bytesRead != 0)
{
bytesRead = fsInput.Read(buffer, 0, bufferLen);
sumBytesRead += bytesRead;
if (sumBytesRead <= numOfDecBytes) //decrypt until limit
{
if (bytesRead < bufferLen)
{
cs.Write(buffer, 0, bytesRead);
decryptedByteCounter += bytesRead;
byteWriteCounter += bytesRead;
bytesRead = 0; //we are at the end of file, end everything
}
else
{
cs.Write(buffer, 0, bytesRead);
decryptedByteCounter += bytesRead;
byteWriteCounter += bytesRead;
}
}
else //if we have decrypted encrypted bytes, continue with rest of the (normal) data
{
if (bytesRead < bufferLen)
{
fsOutput.Write(buffer, 0, bytesRead);
byteWriteCounter += bytesRead;
bytesRead = 0;
}
else
{
fsOutput.Write(buffer, 0, bytesRead);
byteWriteCounter += bytesRead;
}
}
}
}
catch (SystemException se)
{
Console.WriteLine("Exception DECR: " + se);
}
}
}
}
return true;
}
else
{
//not right file for decryption
return false;
}
}
}
catch (SystemException eks)
{
Console.WriteLine("Error: " + eks); //here the exception of Invalid Padding is thrown
return false;
}
}
【问题讨论】：
-
这基本上相当于调试文件处理。您的密文与纯文本一样大的假设是错误的。您完全阅读到要加密的明文末尾的假设似乎也是错误的。密文也可能比明文大。总而言之，许多错误，以及试图做所有事情而不是做出好的设计的加密/解密方法。
-
为什么只想加密部分文件？这显然不安全。
-
@MaartenBodewes-owlstead 我知道，有很多错误，如果它符合我的逻辑，我正在开发阶段测试。但是你能帮助并提供解决方案如何实现加密字节数，在解密中可以计算和解密吗？还是应该使用其他加密算法？
-
@CodesInChaos 我没有找到任何其他解决方案来更快地加密大量 2GB+ (.iso) 文件。如果你对这么大文件的一小部分进行加密，总体结果是一样的——文件不能使用..
-
@OnlyKing 对于 DRM 来说可能是可以接受的（无论如何它已经被破坏了），对于任何与安全相关的东西都不是。如果您只加密开头，一个称职的攻击者将能够从该 iso 文件中提取大多数文件。但即使对于 DRM，它也没有什么意义，因为您只需要在受限于 IO 性能的情况下进行动态解密，而不是解密的 CPU 成本。
标签： c# security encryption cryptography partial