AES and VB.net

[PrOpHeT]

I have constructed the following class from examples on MSDN and elsewhere, for some reason when decrypting I seem to end up with extra bytes and cannot for the life of me figure out where they are coming from.:confused:

I know I am using a block cipher, and my resulting encrypted data can end up with a different byte count, however after decrypting it should be a byte for byte match of the original.

 

I have to be overlooking something, but it is all blending together and I need another set of eyes to have a look.

 

#Region " Imports "

Imports System.IO
Imports System.Text
Imports System.Security.Cryptography

#End Region

Public Class Encryption

   Private Key() As Byte
   Private CryptoEngine As New  AesManaged

   ' ----- Create initialization vector.
   Private IV() As Byte = Encoding.ASCII.GetBytes(Guid.NewGuid.ToString.Replace("-", Nothing).Substring(16))

   ''' <summary>
   ''' Create a new instance of the encryption class using specified passphrase to en/decrypt.
   ''' </summary>
   ''' <param name="PassPhrase">Passphrase to use when en/decrypting data.</param>
   Public Sub New(ByVal PassPhrase As String)
       Dim HashEngine As New MD5CryptoServiceProvider
       Key = HashEngine.ComputeHash(Encoding.ASCII.GetBytes(PassPhrase))
   End Sub

   ''' <summary>
   ''' Converts plain text into base64 encoded 128bit Rijndael(AES) encrypted string.
   ''' </summary>
   ''' <param name="PlainText">Text to be encrypted</param>
   ''' <returns>String</returns>
   Public Overloads Function Encrypt(ByVal PlainText As String) As String
       Return Convert.ToBase64String(Encrypt(Encoding.ASCII.GetBytes(PlainText)))
   End Function

   ''' <summary>
   ''' Converts base64 encoded 128bit Rijndael(AES) encrypted string into plain text.
   ''' </summary>
   ''' <param name="Encrypted">Text to be decrypted</param>
   ''' <returns>String</returns>
   Public Overloads Function Decrypt(ByVal Encrypted As String) As String
       Return Encoding.ASCII.GetString(Decrypt(Convert.FromBase64String(Encrypted))).Replace(vbNullChar, Nothing)
   End Function

   ''' <summary>
   ''' Encrypts array of Byte() using 128bit Rijndael(AES).
   ''' </summary>
   ''' <param name="Data">Byte array to encrypt</param>
   ''' <returns>Encrypted byte array</returns>
   Public Overloads Function Encrypt(ByVal Data() As Byte) As Byte()
       Try

           Dim Tmp_Stream As New MemoryStream()

           Dim Transform As ICryptoTransform
           Transform = CryptoEngine.CreateEncryptor(Key, IV)

           Dim EncryptionStream As CryptoStream
           EncryptionStream = New CryptoStream(Tmp_Stream, Transform, CryptoStreamMode.Write)

           With EncryptionStream
               .Write(Data, 0, Data.Length)
               .FlushFinalBlock()
           End With

           Tmp_Stream.Close()
           EncryptionStream.Close()

           Return Tmp_Stream.ToArray
       Catch ex As Exception
           Debug.WriteLine(ex.Message)
           Return Nothing
       End Try
   End Function

   ''' <summary>
   ''' Decrypts array of Byte() using 128bit Rijndael(AES).
   ''' </summary>
   ''' <param name="Data">Byte array to decrypt</param>
   ''' <returns>decrypted byte array</returns>
   Public Overloads Function Decrypt(ByVal Data() As Byte) As Byte()
       Try

           Dim Tmp_Bytes(Data.Length - 1) As Byte
           Dim Tmp_Stream As New MemoryStream(Data)


           Dim Transform As ICryptoTransform
           Transform = CryptoEngine.CreateDecryptor(Key, IV)

           Dim EncryptionStream As CryptoStream
           EncryptionStream = New CryptoStream(Tmp_Stream, Transform, CryptoStreamMode.Read)

           EncryptionStream.Read(Tmp_Bytes, 0, Tmp_Bytes.Length)

           Tmp_Stream.Close()
           EncryptionStream.Close()

           Return Tmp_Bytes
       Catch ex As Exception
           Debug.WriteLine(ex.Message)
           Return Nothing
       End Try
   End Function

End Class

Edited June 24, 2008 by PrOpHeT

[PrOpHeT]

OK, don't you just hate that just after you ask a question it becomes apparent :mad:

 

It makes perfect sense now I am getting the extra bytes due to the fact i am declaring my read buffer equal to the encrypted bytes (padded for the block cipher *DUH*)

[PrOpHeT]

Hmm, this has raised another interesting question, is how do I know what to dimension my byte array to not knowing what the original data size is?

 

I tried EncryptedStream.Length which is apparently not valid (documentation states "This property exists only to support inheritance from Stream, and cannot be used.") 'O Joy

Edited June 24, 2008 by PrOpHeT

[PrOpHeT]

I found the solution here

 

http://blogs.clearscreen.com/jfbonnin/archive/2007/05/28/6414.aspx