Imports System.Text

''' <summary>
''' Utility class for handling encryption and hashing
''' </summary>
''' <remarks></remarks>
Public NotInheritable Class Encryption

    Private Sub New()

    End Sub

    ''' <summary>
    ''' Returns an encrypted string based on the provided message and passkey
    ''' </summary>
    ''' <param name="message"></param>
    ''' <param name="key"></param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Shared Function Encrypt(ByVal message As String, ByVal key As String) As String

        If message Is Nothing OrElse message.Length = 0 Then
            Throw New ArgumentNullException("message")
        End If

        If key Is Nothing OrElse key.Length = 0 Then
            Throw New ArgumentNullException("key")
        End If

        Dim returnValue As String = String.Empty

        returnValue = EnDeCrypt(message, key)
        returnValue = StringToHex(returnValue)

        Return returnValue

    End Function

    ''' <summary>
    ''' Returns a decrypted string based on the provided message and passkey
    ''' </summary>
    ''' <param name="message"></param>
    ''' <param name="key"></param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Shared Function Decrypt(ByVal message As String, ByVal key As String) As String

        If message Is Nothing OrElse message.Length = 0 Then
            Throw New ArgumentNullException("message")
        End If

        If key Is Nothing OrElse key.Length = 0 Then
            Throw New ArgumentNullException("key")
        End If

        Dim returnValue As String = String.Empty

        returnValue = HexToString(message)
        returnValue = EnDeCrypt(returnValue, key)

        Return returnValue

    End Function

    ''' <summary>
    ''' RC4 encryption method
    ''' </summary>
    ''' <param name="message"></param>
    ''' <param name="password"></param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Private Shared Function EnDeCrypt(ByVal message As String, ByVal password As String) As String

        Dim i As Integer = 0
        Dim j As Integer = 0
        Dim cipher As New StringBuilder
        Dim returnCipher As String = String.Empty

        Dim sbox As Integer() = New Integer(256) {}
        Dim key As Integer() = New Integer(256) {}

        Dim intLength As Integer = password.Length

        Dim a As Integer = 0
        While a <= 255

            Dim ctmp As Char = (password.Substring((a Mod intLength), 1).ToCharArray()(0))

            key(a) = Microsoft.VisualBasic.Strings.Asc(ctmp)
            sbox(a) = a
            System.Math.Max(System.Threading.Interlocked.Increment(a), a - 1)
        End While

        Dim x As Integer = 0

        Dim b As Integer = 0
        While b <= 255
            x = (x + sbox(b) + key(b)) Mod 256
            Dim tempSwap As Integer = sbox(b)
            sbox(b) = sbox(x)
            sbox(x) = tempSwap
            System.Math.Max(System.Threading.Interlocked.Increment(b), b - 1)
        End While

        a = 1

        While a <= message.Length

            Dim itmp As Integer = 0

            i = (i + 1) Mod 256
            j = (j + sbox(i)) Mod 256
            itmp = sbox(i)
            sbox(i) = sbox(j)
            sbox(j) = itmp

            Dim k As Integer = sbox((sbox(i) + sbox(j)) Mod 256)

            Dim ctmp As Char = message.Substring(a - 1, 1).ToCharArray()(0)

            itmp = Asc(ctmp)

            Dim cipherby As Integer = itmp Xor k

            cipher.Append(Chr(cipherby))
            System.Math.Max(System.Threading.Interlocked.Increment(a), a - 1)
        End While

        returnCipher = cipher.ToString
        cipher.Length = 0

        Return returnCipher

    End Function

    ''' <summary>
    ''' Turns the provided string value into a hex value (for encryption)
    ''' </summary>
    ''' <param name="message"></param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Private Shared Function StringToHex(ByVal message As String) As String

        Dim index As Long
        Dim maxIndex As Long
        Dim hexSb As New StringBuilder
        Dim hexOut As String = String.Empty

        maxIndex = Len(message)

        For index = 1 To maxIndex
            hexSb.Append(Right("0" & Hex(Asc(Mid(message, CInt(index), 1))), 2))
        Next

        hexOut = hexSb.ToString
        hexSb.Length = 0

        Return hexOut

    End Function

    ''' <summary>
    ''' Turns the provided hex value into a string value (for decryption)
    ''' </summary>
    ''' <param name="hex"></param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Private Shared Function HexToString(ByVal hex As String) As String

        Dim index As Long
        Dim maxIndex As Long
        Dim sb As New StringBuilder
        Dim returnString As String = String.Empty

        maxIndex = Len(hex)

        For index = 1 To maxIndex Step 2
            sb.Append(Chr(CInt("&h" & Mid(hex, CInt(index), 2))))
        Next

        returnString = sb.ToString
        sb.Length = 0

        Return returnString

    End Function

End Class