Imports java.math
Imports System.Diagnostics



Module Module1
    ' this class shall be the stream cryptogropher
    Private Class StreamCrypto
        ' this class shall be the cryptographically secure pseudorandom number generator
        ' to be used by the stream cryptographer
        Private Class BlumBlumShubChar
            'Blum Blum Shub (B.B.S.) is a pseudorandom number generator proposed in 1986 by
            'Lenore Blum, Manuel Blum and Michael Shub (Blum et al., 1986).
            'Blum Blum Shub takes the form:
            'x_{n+1} = {x_n}^2 mod M
            'where M=pq is the product of two large primes p and q (which will be primes just below 2^256 in our case, making M close to 2^512)
            ' the constructor, takes a seed for the random number egenrator as input
            Public Sub New(ByVal seed As String)
                ' this chararray will hold the seed string after its been converted to a array of ascii chars
                Dim chararray(seed.Length - 1) As SByte
                ' blockmodulo is a biginteger object which will always contain the number 2^128
                ' blockmodulo = 2^128
                blockmodulo = New BigInteger(2)
                blockmodulo = blockmodulo.pow(128)
                ' blockmodulo = BigInteger.Pow(2, 128)
                ' M is the product of 2 primes just below 256
                ' M is the almost-prime modulo that will be used for all the modulos henceforth
                ' this class provides M-bit encryption when used in stream cryptography
                ' M = ((2^256)-189)*((2^256)-357)

                Dim p As New BigInteger(2)
                p = p.pow(256)
                p = p.subtract(New BigInteger(357))

                Dim q As New BigInteger(2)
                q = q.pow(256)
                q = q.subtract(New BigInteger(189))

                'M = BigInteger.Multiply(BigInteger.Pow(2, 256) - 189, BigInteger.Pow(2, 256) - 357)
                M = q.multiply(p)
                ' copy the seed string to the chararray declared earlier
                For i As UInt16 = 0 To seed.Length - 1
                    chararray(i) = Asc(seed.Substring(i, 1)) - 127
                Next
                ' generate the first x from the seed string in the char-array
                x = New BigInteger(chararray)
                ' mod x by M
                x = x.mod(M)
                ' x = BigInteger.ModPow(x, 1, M)
                ' generate the first pseudorandom number, hence randomizing x
                Generate()
            End Sub
            ' the generator returns a block of 16 bytes
            ' this is equal to a number between 0 and (2^128)-1
            ' so the x must be modded by 2^128 to get a 16-byte number
            Public Function Generate() As Byte()
                'x_{n+1} = {x_n}^2 mod M
                x = x.modPow(New BigInteger(2), M)
                ' op is the output byte array
                ' it is set to x mod 2^128
                Dim top As SByte() = x.mod(blockmodulo).toByteArray()
                Dim op(15) As Byte
                For i As UInt16 = 0 To 15
                    op(i) = 0
                Next
                For i As UInt16 = 0 To System.Math.Min(15, top.Length - 1)
                    Dim temp As Int16 = top(i)
                    temp += 128
                    op(i) = temp
                Next
                ' shorten the byte array to 16, we dont need any more
                'Array.Resize(op, 16)
                ' return op
                Return op
            End Function
            Private blockmodulo As BigInteger
            Private M As BigInteger
            Private x As BigInteger
        End Class

        Public Function Crypt(ByVal input As String, ByVal key As String) As String
            Dim stopWatch As New Stopwatch()
            stopWatch.Start()
            ' create a new random number generator
            Dim c As New BlumBlumShubChar(key)
            ' create a chararray to hold the string *yawn*
            Dim chararray(input.Length - 1) As Char
            ' copy string to chararray
            For i As UInt16 = 0 To input.Length - 1
                chararray(i) = input.Substring(i, 1)
            Next
            ' k is how far we are through the current block of random buytes
            Dim k As UInt16 = 0
            ' block holds the block of random bytes
            Dim block(16) As Byte
            ' generate and discard a block to confuse hackers
            c.Generate()
            ' generate a block and keep
            block = c.Generate()
            ' cycle through the input string
            For i As UInt16 = 0 To input.Length - 1
                ' if weve polished off the current block, get a new one and reset the block counter
                If k >= 16 Then
                    c.Generate()
                    block = c.Generate()
                    k = 0
                End If
                ' exclusive-or the current byte in the block counter with the ascii code of the priginal string
                ' and store back into the string
                'Console.WriteLine((block(k)))
                chararray(i) = Chr(block(k) Xor Asc(chararray(i)))
                ' increment block counter
                k += 1
            Next
            ' copy the char array back into a new string and return
            Dim output As String = ""
            For i As UInt16 = 0 To input.Length - 1
                output &= chararray(i)
            Next
            stopWatch.Stop()
            Console.WriteLine("This took " & stopWatch.ElapsedMilliseconds & " milliseconds ")
            Return output
        End Function
    End Class

    Sub Main()
        'Dim lol As New StreamCrypto.BlumBlumShubChar("hammertime")
        'While True
        '    Console.WriteLine(Chr(lol.Generate()))
        '    'Console.ReadLine()
        'End While
        Dim lol As New StreamCrypto
        While True
            Console.WriteLine("i can has key?")
            Dim key As String = Console.ReadLine()
            Console.WriteLine("i can haz plaintext?")
            Dim plaintext As String = Console.ReadLine()
            Console.WriteLine("i gives you ciphertext:")
            Dim ciphertext As String = lol.Crypt(plaintext, key)
            Console.WriteLine(ciphertext)
            Console.WriteLine("i gives you plaintext again:")
            Console.WriteLine(lol.Crypt(ciphertext, key))
            Console.ReadLine()
        End While
    End Sub

End Module