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

Public Class clsEncoder
    Public Function EncryptString128Bit(ByVal vstrTextToBeEncrypted As String, _
                                        ByVal vstrEncryptionKey As String) As String

        Dim bytValue() As Byte
        Dim bytKey() As Byte
        Dim bytEncoded() As Byte
        Dim bytIV() As Byte = {121, 241, 10, 1, 132, 74, 11, 39, 255, 91, 45, 78, 14, 211, 22, 62}
        Dim intLength As Integer
        Dim intRemaining As Integer
        Dim objMemoryStream As New MemoryStream()
        Dim objCryptoStream As CryptoStream
        Dim objRijndaelManaged As RijndaelManaged




        '   **********************************************************************
        '   ******  Strip any null character from string to be encrypted    ******
        '   **********************************************************************

        vstrTextToBeEncrypted = StripNullCharacters(vstrTextToBeEncrypted)

        '   **********************************************************************
        '   ******  Value must be within ASCII range (i.e., no DBCS chars)  ******
        '   **********************************************************************

        bytValue = Encoding.ASCII.GetBytes(vstrTextToBeEncrypted.ToCharArray)

        intLength = Len(vstrEncryptionKey)

        '   ********************************************************************
        '   ******   Encryption Key must be 256 bits long (32 bytes)      ******
        '   ******   If it is longer than 32 bytes it will be truncated.  ******
        '   ******   If it is shorter than 32 bytes it will be padded     ******
        '   ******   with upper-case Xs.                                  ****** 
        '   ********************************************************************

        If intLength >= 32 Then
            vstrEncryptionKey = Strings.Left(vstrEncryptionKey, 32)
        Else
            intLength = Len(vstrEncryptionKey)
            intRemaining = 32 - intLength
            vstrEncryptionKey = vstrEncryptionKey & Strings.StrDup(intRemaining, "X")
        End If

        bytKey = Encoding.ASCII.GetBytes(vstrEncryptionKey.ToCharArray)

        objRijndaelManaged = New RijndaelManaged()

        '   ***********************************************************************
        '   ******  Create the encryptor and write value to it after it is   ******
        '   ******  converted into a byte array                              ******
 
        Try

            objCryptoStream = New CryptoStream(objMemoryStream, _
              objRijndaelManaged.CreateEncryptor(bytKey, bytIV), _
              CryptoStreamMode.Write)
            objCryptoStream.Write(bytValue, 0, bytValue.Length)

            objCryptoStream.FlushFinalBlock()

            bytEncoded = objMemoryStream.ToArray
            objMemoryStream.Close()
            objCryptoStream.Close()
        Catch



        End Try

        '   ***********************************************************************
        '   ******   Return encryptes value (converted from  byte Array to   ******
        '   ******   a base64 string).  Base64 is MIME encoding)             ******
        '   ***********************************************************************

        Return Convert.ToBase64String(bytEncoded)

    End Function




    Public Function DecryptString128Bit(ByVal vstrStringToBeDecrypted As String, _
                                        ByVal vstrDecryptionKey As String) As String

        Dim bytDataToBeDecrypted() As Byte
        Dim bytTemp() As Byte
        Dim bytIV() As Byte = {121, 241, 10, 1, 132, 74, 11, 39, 255, 91, 45, 78, 14, 211, 22, 62}
        Dim objRijndaelManaged As New RijndaelManaged()
        Dim objMemoryStream As MemoryStream
        Dim objCryptoStream As CryptoStream
        Dim bytDecryptionKey() As Byte

        Dim intLength As Integer
        Dim intRemaining As Integer
        'Dim intCtr As Integer
        Dim strReturnString As String = String.Empty
        'Dim achrCharacterArray() As Char
        'Dim intIndex As Integer

        '   *****************************************************************
        '   ******   Convert base64 encrypted value to byte array      ******
        '   *****************************************************************

        bytDataToBeDecrypted = Convert.FromBase64String(vstrStringToBeDecrypted)

        '   ********************************************************************
        '   ******   Encryption Key must be 256 bits long (32 bytes)      ******
        '   ******   If it is longer than 32 bytes it will be truncated.  ******
        '   ******   If it is shorter than 32 bytes it will be padded     ******
        '   ******   with upper-case Xs.                                  ****** 
        '   ********************************************************************

        intLength = Len(vstrDecryptionKey)

        If intLength >= 32 Then
            vstrDecryptionKey = Strings.Left(vstrDecryptionKey, 32)
        Else
            intLength = Len(vstrDecryptionKey)
            intRemaining = 32 - intLength
            vstrDecryptionKey = vstrDecryptionKey & Strings.StrDup(intRemaining, "X")
        End If

        bytDecryptionKey = Encoding.ASCII.GetBytes(vstrDecryptionKey.ToCharArray)

        ReDim bytTemp(bytDataToBeDecrypted.Length)

        objMemoryStream = New MemoryStream(bytDataToBeDecrypted)

        '   ***********************************************************************
        '   ******  Create the decryptor and write value to it after it is   ******
        '   ******  converted into a byte array                              ******
        '   ***********************************************************************

        Try

            objCryptoStream = New CryptoStream(objMemoryStream, _
               objRijndaelManaged.CreateDecryptor(bytDecryptionKey, bytIV), _
               CryptoStreamMode.Read)

            objCryptoStream.Read(bytTemp, 0, bytTemp.Length)

            objCryptoStream.FlushFinalBlock()
            objMemoryStream.Close()
            objCryptoStream.Close()

        Catch

        End Try

        '   *****************************************
        '   ******   Return decypted value     ******
        '   *****************************************

        Return StripNullCharacters(Encoding.ASCII.GetString(bytTemp))

    End Function


    Public Function StripNullCharacters(ByVal vstrStringWithNulls As String) As String

        Dim intPosition As Integer
        Dim strStringWithOutNulls As String

        intPosition = 1
        strStringWithOutNulls = vstrStringWithNulls

        Do While intPosition > 0
            intPosition = InStr(intPosition, vstrStringWithNulls, vbNullChar)

            If intPosition > 0 Then
                strStringWithOutNulls = Left$(strStringWithOutNulls, intPosition - 1) & _
                                  Right$(strStringWithOutNulls, Len(strStringWithOutNulls) - intPosition)
            End If

            If intPosition > strStringWithOutNulls.Length Then
                Exit Do
            End If
        Loop

        Return strStringWithOutNulls

    End Function


End Class