AesCryptoServiceProvider的默认填充是什么？

Question

当我试图使用Padding is invalid and cannot be removed解密字符串时，我得到了错误的AesCryptoServiceProvider。根据这问题，我需要在加密和解密算法上指定相同的填充。我遇到的问题是，在没有显式填充的情况下，已经对数据进行了加密。在这种情况下使用的默认填充是什么，这样我就可以显式地设置它了？

下面是正在使用的代码：

public static byte[] EncryptStringToBytes(string plainText, byte[] Key, byte[] IV)
{
  // Check arguments. 
  if (plainText == null || plainText.Length <= 0)
    throw new ArgumentNullException("plainText");
  if (Key == null || Key.Length <= 0)
    throw new ArgumentNullException("Key");
  if (IV == null || IV.Length <= 0)
    throw new ArgumentNullException("Key");
  byte[] encrypted;
  // Create an AesCryptoServiceProvider object 
  // with the specified key and IV. 
  using (AesCryptoServiceProvider aesAlg = new AesCryptoServiceProvider())
  {
    aesAlg.Key = Key;
    aesAlg.IV = IV;
    // Create a decrytor to perform the stream transform.
    ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);

    // Create the streams used for encryption. 
    using (MemoryStream msEncrypt = new MemoryStream())
    {
      using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
      {
        using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
        {
          //Write all data to the stream.
          swEncrypt.Write(plainText);
        }
        encrypted = msEncrypt.ToArray();
      }
    }
  }
  // Return the encrypted bytes from the memory stream. 
  return encrypted;
}

public static string DecryptStringFromBytes(byte[] cipherText, byte[] Key, byte[] IV)
{
  // Check arguments. 
  if (cipherText == null || cipherText.Length <= 0)
    throw new ArgumentNullException("cipherText");
  if (Key == null || Key.Length <= 0)
    throw new ArgumentNullException("Key");
  if (IV == null || IV.Length <= 0)
    throw new ArgumentNullException("Key");

  string plaintext = null;
  using (AesCryptoServiceProvider aesAlg = new AesCryptoServiceProvider())
  {
    aesAlg.Key = Key;
    aesAlg.IV = IV;

    ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
    using (MemoryStream msDecrypt = new MemoryStream(cipherText))
    {
      using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
      {
        using (StreamReader srDecrypt = new StreamReader(csDecrypt))
        {
          plaintext = srDecrypt.ReadToEnd();
        }
      }
    }
  }
  return plaintext;
}

Key和IV是使用给出password和salt的Rfc2898DeriveBytes检索的。贝娄是密码：

public static void GetKeyAndIVFromPasswordAndSalt(string password, byte[] salt, SymmetricAlgorithm symmetricAlgorithm, ref byte[] key, ref byte[] iv)
{
  Rfc2898DeriveBytes rfc2898DeriveBytes = new Rfc2898DeriveBytes(password, salt);
  key = rfc2898DeriveBytes.GetBytes(symmetricAlgorithm.KeySize / 8);
  iv = rfc2898DeriveBytes.GetBytes(symmetricAlgorithm.BlockSize / 8);
}

Answer 1

对称算法的默认模式可以在MSDN的SymmetricAlgorithm属性页面中找到。在本例中，PaddingMode.PKCS7是使用的默认填充模式。

但是，请注意，这个特定的密码异常也可以在不同的情况下抛出。如果您的密钥和/或IV与数据加密中使用的密钥和/或IV不完全相同，则将引发此异常。您所链接的问题中的第二个答案将讨论这一点。