AES and VB.net

P

PrOpHeT

Freshman
Joined
Sep 1, 2004
Messages
29
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.

Code: 
#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
 
Last edited:
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*)
 
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
 
Last edited:
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