XorUInt64 -TizzyT

    Public Structure XorUInt64
        Private Shared Rnd As Random
        Private StoredValue As UInt64
        Private TokenHash ,ValueHash As Byte
        Private Function RndUInt64() As UInt64
            Dim ULongBytes(7) As Byte
            Rnd.NextBytes(ULongBytes)
            Return BitConverter.ToUInt64(ULongBytes, 0)
        End Function
        Private Function Hash(ByVal Token As UInt64) As Byte
            Dim TokenBytes() As Byte = BitConverter.GetBytes(Token)
            Dim HashCode As Int16 = TokenBytes(0)
            HashCode += TokenBytes(1) Xor 170
            HashCode += TokenBytes(2) Xor 170
            HashCode += TokenBytes(3) Xor 170
            HashCode += TokenBytes(4) Xor 170
            HashCode += TokenBytes(5) Xor 170
            HashCode += TokenBytes(6) Xor 170
            HashCode += TokenBytes(7) Xor 170
            Return HashCode Mod 256
        End Function
        Public Sub New(ByRef Token As UInt64)
            Rnd = New Random
            Token = RndUInt64()
            TokenHash = Hash(Token)
        End Sub
        Public Sub Store(ByRef Token As UInt64, ByVal Value As UInt64)
            If Hash(Token) = TokenHash Then
                Token = RndUInt64()
                TokenHash = Hash(Token)
                ValueHash = Hash(Value)
                StoredValue = Token Xor Value
            Else
                Throw New Exception("Token hash mismatch")
            End If
        End Sub
        Default Public ReadOnly Property Value(ByVal Token As UInt64) As UInt64
            Get
                If Hash(Token) <> TokenHash Then Throw New Exception("Token hash mismatch")
                Dim R As UInt64 = StoredValue Xor Token
                If Hash(R) = ValueHash Then Return R Else Throw New Exception("Return value inconsistent with stored value")
            End Get
        End Property
    End Structure