Public Class RC4Crypter
 
    Private _key As String
 
    Public Sub New(ByVal key As String)
        _key = key
    End Sub
 
    Public Function Crypt(ByVal data() As Byte) As Byte()
 
        RC4(data, ASCII.GetBytes(_key))
        Return data
 
    End Function
 
    Private Sub RC4(ByRef bytes() As Byte, ByRef key() As Byte)
 
        Dim s(256) As Byte
        Dim k(256) As Byte
        Dim temp As Byte
        Dim i, j, t, x As Integer
 
        'S-Box füllen
        For i = 0 To 255
            s(i) = CByte(i)
            k(i) = key(i Mod key.Length)
        Next
 
        'S-Box verändern
        j = 0
        For i = 0 To 255
            j = (j + s(i) + k(i)) Mod 256
            swap(s(i), s(j))
        Next
 
        'Verschlüsseln
 
        i = j = 0
 
        For x = 0 To bytes.Length - 1
            i = (i + 1) Mod 256
            j = (j + s(i)) Mod 256
            swap(s(i), s(j))
            t = (CInt(s(i)) + CInt(s(j))) Mod 256
            bytes(x) = t Xor bytes(x)
        Next
    End Sub
 
    Private Sub swap(ByRef a As Byte, ByRef b As Byte)
        Dim temp As Byte
        temp = a
        a = b
        b = temp
    End Sub
End Class