c# - "Padding is invalid and cannot be removed"使用 AesManaged

Question

我正在尝试使用 AesManaged 进行简单的加密/解密，但在尝试关闭解密流时我总是遇到异常。此处的字符串被正确加密和解​​密，然后在 Console.WriteLine 打印出正确的字符串后我得到 CryptographicException“填充无效且无法删除”。

有什么想法吗？

MemoryStream ms = new MemoryStream();
byte[] rawPlaintext = Encoding.Unicode.GetBytes("This is annoying!");

using (Aes aes = new AesManaged())
{
  aes.Padding = PaddingMode.PKCS7;
  aes.Key = new byte[128/8];
  aes.IV = new byte[128/8];

  using (CryptoStream cs = new CryptoStream(ms, aes.CreateEncryptor(),
                                            CryptoStreamMode.Write))
  {
    cs.Write(rawPlaintext, 0, rawPlaintext.Length);
    cs.FlushFinalBlock();
  }

  ms = new MemoryStream(ms.GetBuffer());
  using (CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(),
                                            CryptoStreamMode.Read))
  {
    byte[] rawData = new byte[rawPlaintext.Length];
    int len = cs.Read(rawData, 0, rawPlaintext.Length);
    string s = Encoding.Unicode.GetString(rawData);
    Console.WriteLine(s);
  }
}

Answer 1

诀窍是使用 MemoryStream.ToArray()。我还更改了您的代码，以便它在加密和解密时都使用 CryptoStream 进行写入。而且您不需要显式调用 CryptoStream.FlushFinalBlock()，因为您在 using() 语句中拥有它，并且刷新将在 Dispose 上发生()。以下对我有用。

byte[] rawPlaintext = System.Text.Encoding.Unicode.GetBytes("This is all clear now!");

using (Aes aes = new AesManaged())
{
    aes.Padding = PaddingMode.PKCS7;
    aes.KeySize = 128;          // in bits
    aes.Key = new byte[128/8];  // 16 bytes for 128 bit encryption
    aes.IV = new byte[128/8];   // AES needs a 16-byte IV
    // Should set Key and IV here.  Good approach: derive them from 
    // a password via Cryptography.Rfc2898DeriveBytes 
    byte[] cipherText= null;
    byte[] plainText= null;

    using (MemoryStream ms = new MemoryStream())
    {
        using (CryptoStream cs = new CryptoStream(ms, aes.CreateEncryptor(), CryptoStreamMode.Write))
        {
            cs.Write(rawPlaintext, 0, rawPlaintext.Length);
        }

        cipherText= ms.ToArray();
    }


    using (MemoryStream ms = new MemoryStream())
    {
        using (CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Write))
        {
            cs.Write(cipherText, 0, cipherText.Length);
        }

        plainText = ms.ToArray();
    }
    string s = System.Text.Encoding.Unicode.GetString(plainText);
    Console.WriteLine(s);
}

另外，我猜你知道你会想要显式设置 Mode的 AesManaged 实例，并使用 System.Security.Cryptography.Rfc2898DeriveBytes从密码和盐派生 key 和 IV。

另见:
- AesManaged