Please Test This Encryption Scheme

[Jack_the_box]

Here is a basic version of an encryption sscheme i devloped.
If you have the time and the knowledge please test it.
[list=A][*]Is it a strong encryption?[*]Did you brake it? How?[*]Any ideas for improvement?[/list=A]

Global dKey as Double,sKey as Double,D(255) As Byte
Function Encrypt(OriginalFile)
        'Promt user to enter a Key: call Key(text1.text) 
        sfile=OriginalFile 
        Rnd (-dKey): Randomize dKey
        
        xfile = sfile & ".stdenc"
        Open sfile For Random As #1 Len = 1
        lenfile = LOF(1)
        Close
        
        ReDim C(lenfile) As Byte, x(lenfile) As Byte
        Open sfile For Binary As #1
        Get #1, 1, C()
        Close
        y = 0
        
        For i = 1 To lenfile
            y = y + 1
            y = y Mod 255 + 1
            x(i) = C(i) Xor D(y)
        Next i
        
        Open xfile For Binary As #1
        Put #1, 1, x()
        Close
End Function

Private Sub Key (x as String)

For i = 1 To (Len(x) - 1)
    t = t + Asc(Mid(x, i, 1))
Next i
t = t - Asc(Mid(x, Len(x), 1))
t = t ^ 2 - t
Rnd (-t)
Randomize t

sKey = Int(Rnd * 2123234345) + 2000398
dKey = Int(sKey / 1000 + 603)

Rnd (-sKey)
Randomize sKey

For i = 1 To 255
    g = Int(Rnd * 255) + 1
    h = Int(Rnd * 255) + 1
    D(i) = g Xor h
Next i

End Sub

Let me know what you think

[Jack_the_box]

A breif explaination:
First, the key is not stored in the encrypted file. A numder, i.e. TestNum, is created in the Key( ) sub, and stored in the encrypted file.
The Key verification uses the User inputed key and the Key( ) sub to create a TestNum. If the TestNum created by Key( ) is the same as
the TestNum in the encrypted file, then the encrypted file is decrypted.

Second, the plainFile(unencrypted file) is loaded into an array.

       Open sfile For Random As #1 Len = 1
        lenfile = LOF(1)
        Close
        
        ReDim C(lenfile) As Byte, x(lenfile) As Byte 'Create the array
        Open sfile For Binary As #1
        Get #1, 1, C() 'load whole file into array
        Close

The array C( ) is then encrypted.

       For i = 1 To lenfile
            y = y + 1
            y = y Mod 255 + 1
            x(i) = C(i) Xor D(y)
        Next i

This method is faster than reading one byte, encrypting it, and then writing it.