使用C＃进行AES加密的密文长度是多少？

Question

发件人： Can we calculate AES ciphertext length based on the length of the plaintext?

我看到：output_size = input_size +（16-（input_size％16））

但是，这似乎与我使用C＃和带有PKCS7填充和CBC CipherMode的AesCng运行测试时看到的不一致。

关于我如何计算加密值的长度的想法？

这是示例程序的代码：

Public Shared Function Encrypt(ByVal plainText As String, ByVal aes256BitKeyValue As String, ByVal initialVector As String) As String

  If String.IsNullOrEmpty(plainText) Then
    Return String.Empty
  End If

  Dim initialVectorBytes As Byte() = System.Text.Encoding.ASCII.GetBytes(initialVector)
  Dim plainTextBytes As Byte() = System.Text.Encoding.UTF8.GetBytes(plainText)
  Dim cipherTextBytes As Byte() = Nothing

  Using symmetricKey As New System.Security.Cryptography.AesCng()
    symmetricKey.Padding = Security.Cryptography.PaddingMode.PKCS7
    symmetricKey.Mode = System.Security.Cryptography.CipherMode.CBC

    Dim keyBytes As Byte() = StringToByteArray(aes256BitKeyValue)

    Try

      Using cryptographyTransform As System.Security.Cryptography.ICryptoTransform = symmetricKey.CreateEncryptor(keyBytes, initialVectorBytes)
        Using memoryStream As New System.IO.MemoryStream()
          Using cryptographyStream As New System.Security.Cryptography.CryptoStream(memoryStream, cryptographyTransform, System.Security.Cryptography.CryptoStreamMode.Write)
            cryptographyStream.Write(plainTextBytes, 0, plainTextBytes.Length)
            cryptographyStream.FlushFinalBlock()
            cipherTextBytes = memoryStream.ToArray()
            memoryStream.Close()
            cryptographyStream.Close()
          End Using
        End Using
      End Using

    Catch ex As Exception
      Throw New Exceptions.EncryptionException(String.Format(System.Globalization.CultureInfo.InvariantCulture, Resources.ExceptionMessages.EncryptionFailed1, ex))

    Finally
      symmetricKey.Clear()
    End Try

  End Using

  Return Convert.ToBase64String(cipherTextBytes)

End Function

命名空间ConsoleApplication1 {   班级计划   {     静态void Main（string [] args）     {       字符串aes256Key =“ 1234567890123456789012345678901234567890123456789012345678901234”;       字符串initialVector =“ 66sDeG * 3xsS334dE”;

  string unencrypted20Text = "12345678901234567890";
  string unencrypted40Text = "1234567890123456789012345678901234567890";
  string unencrypted64Text = "1234567890123456789012345678901234567890123456789012345678901234";
  string unencrypted128Text = "12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678";
  string unencrypted256Text = "1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456";
  string unencrypted257Text = "12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567";
  string unencrypted512Text = unencrypted256Text + unencrypted256Text;
  string unencrypted1024Text = unencrypted512Text + unencrypted512Text;
  string unencrypted2048Text = unencrypted1024Text + unencrypted1024Text;
  string unencrypted4096Text = unencrypted2048Text + unencrypted2048Text;
  string unencrypted8192Text = unencrypted4096Text + unencrypted4096Text;

  string encrypted20Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted20Text, aes256Key, initialVector);
  string encrypted40Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted40Text, aes256Key, initialVector);
  string encrypted64Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted64Text, aes256Key, initialVector);
  string encrypted128Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted128Text, aes256Key, initialVector);
  string encrypted256Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted256Text, aes256Key, initialVector);
  string encrypted257Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted257Text, aes256Key, initialVector);
  string encrypted512Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted512Text, aes256Key, initialVector);
  string encrypted1024Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted1024Text, aes256Key, initialVector);
  string encrypted2048Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted2048Text, aes256Key, initialVector);
  string encrypted4096Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted4096Text, aes256Key, initialVector);
  string encrypted8192Text = Grb.Core.Cryptography.AesEncryption.Encrypt(unencrypted8192Text, aes256Key, initialVector);

  int encrypted20TextLength = encrypted20Text.Length; // actual: 44, expected 20 + (16 - 4) = 32
  int encrypted40TextLength = encrypted40Text.Length; // actual: 64, expected 40 + (116 - 8) = 48
  int encrypted64TextLength = encrypted64Text.Length; // actual: 108, expected 64 + (16 - 0) = 80
  int encrypted128TextLength = encrypted128Text.Length; // actual: 192, expected 128 + (16 - 0) = 144
  int encrypted256TextLength = encrypted256Text.Length; // actual: 364 
  int encrypted257TextLength = encrypted257Text.Length; // actual: 364
  int encrypted512TextLength = encrypted512Text.Length; // actual: 704
  int encrypted1024TextLength = encrypted1024Text.Length; // actual: 1388
  int encrypted2048TextLength = encrypted2048Text.Length; // actual: 2752
  int encrypted4096TextLength = encrypted4096Text.Length; // actual: 5484
  int encrypted8192TextLength = encrypted8192Text.Length; // actual: 10944



}

} }