Algorithms

Imports System.Numerics

Public Class BlumBlumShub

    Private _x As BigInteger
    Private _p As BigInteger
    Private _q As BigInteger
    Private _m As BigInteger

    Private _pow As New BigInteger(2)

    Public Function NextNumber() As BigInteger
        _x = BigInteger.ModPow(_x, _pow, _m)
        Return _x
    End Function

    Public Sub New(ByVal seed As BigInteger)
        _p = BigInteger.Parse("32416190071")
        _q = BigInteger.Parse("32416185031")
        _x = seed
        _m = BigInteger.Multiply(_p, _q)
    End Sub

End Class

Public Class RandomBitStream

    Private _b As BlumBlumShub

    Public Function ReadByte() As Byte
        Dim num As Byte = 0
        For i = 1 To 8
            num += Math.Pow(i, 2) * If(_b.NextNumber().IsEven, 1, 0)
        Next
        Return num
    End Function

    Public Sub New(ByVal seed As BigInteger)
        _b = New BlumBlumShub(seed)
    End Sub

End Class

Public Class BlumXor

    Private _bitSrc As RandomBitStream
    Private _key As BigInteger

    Public Sub Cipher(ByRef message As Byte())
        _bitSrc = New RandomBitStream(_key)
        For i = 0 To message.Length - 1
            message(i) = _bitSrc.ReadByte() Xor message(i)
        Next
    End Sub

    Public Function ByteToStr(ByVal inByte As Byte) As String
        Return inByte.ToString().PadLeft(3, "0")
    End Function

    Public Sub New(ByVal keyStr As String)
        Dim encoder As New System.Text.ASCIIEncoding()
        Dim keyBytes As Byte() = encoder.GetBytes(keyStr)
        _key = BigInteger.Parse(String.Join("", Array.ConvertAll(Of Byte, String)(keyBytes, New System.Converter(Of Byte, String)(AddressOf ByteToStr))))
    End Sub

End Class