Open/Read a binary file - access rights - vb.net

Question

I am trying to convert VB5 to .NET and cannot get a binary read to work. My VB.NET decode only reads the first two characters correctly.
The (VB5->VB.NET) encode is
' Open file
x = Rnd(-mKeyValue)
filenum = FreeFile()
Try
FileOpen(filenum, Filename, OpenMode.Binary)
Catch ex As IO.IOException
MsgBox(ex.ToString, MsgBoxStyle.Critical, "File opening error")
Exit Sub
End Try
' write data
filecontents = ""
For i = 1 To Len(stringdate)
charnum = Asc(Mid(stringdate, i, 1))
randomint = Int(256 * Rnd())
charnum = charnum Xor randomint
singlechar = Chr(charnum)
FilePut(filenum, singlechar, i)
filecontents = filecontents & singlechar
Next i
And the (VB5->VB.NET) decode is
x = Rnd(-mKeyValue)
filenum = FreeFile()
FileOpen(filenum, Filename, OpenMode.Binary)
For i = 1 To LOF(filenum)
'To VB.NET
FileGet(filenum, singlechar, i)
charnum = Asc(singlechar)
Debug.Print("VB5 singlechar = " & singlechar)
randomint = Int(256 * Rnd())
charnum = charnum Xor randomint
singlechar = Chr(charnum)
Next i
My VB.NET code which fails (cannot read the file correctly) is;
Using reader As New BinaryReader(File.Open(Filename, FileMode.Open))
' Loop through length of file.
Dim pos As Integer = 0
Dim length As Integer = reader.BaseStream.Length
While pos < length
' Read the integer.
singlechar = reader.ReadChar()
charnum = Asc(singlechar) 'singlechar is type Char
randomint = Int(256 * Rnd())
charnum = charnum Xor randomint
singlechar = Chr(charnum)
i += 1
End While
End Using
Can anyone help me with translation from VB5 to .NET?

Answer 1

In VB.Net everything is a bit shorter ;)
' get a string from an encrypted file file:
Dim b() As Byte = IO.File.ReadAllBytes("path")
For i = 0 To b.Length - 1
b(i) = b(i) Xor (256 * Rnd())
Next
Dim s As String = System.Text.Encoding.ASCII.GetString(b)
Why read byte by byte (no sense to read 'char' anyway, since you only want the 8bit ASCII code), when .Net can read it at once? Your file is not larger > 100 MB, I assume? Then after getting the array, you simply XOR each element with your "random" value. If you dont need to be compatible to old versions, you might better use Random. Or maybe even better ... USE REAL ENCRYPTION (in .Net it's built-in!)
' put a string into a file
Dim c() As Byte = System.Text.Encoding.ASCII.GetBytes("The String you want to store encrypted")
For i = 0 To c.Length - 1
c(i) = c(i) Xor (256 * Rnd())
Next
IO.File.WriteAllBytes("another path", c)
Same for "encrypting". Convert the string to an array of byte (=ASCII values), XOR it and then write it back in ONE operation.
See the dangers of Unicode:
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
' Beware of UNICODE ... !!!
Using sw As New FileStream("foo.foo", FileMode.OpenOrCreate, FileAccess.Write)
' with old VB you effectively wrote BYTE data
sw.Write({65, 192}, 0, 2)
End Using
Using br As New BinaryReader(File.Open("foo.foo", FileMode.Open, FileAccess.Read))
' You are telling. Net that you expect a CHAR, which is not ASCII, but UNICODE
Dim c As Char = br.ReadChar
Dim d As Char = br.ReadChar
Dim cc = Asc(c)
Dim dd = Asc(d)
Debug.Print("65 -> {0}, 192 -> {1}", cc, dd)
End Using
End Sub
The output is 65 -> 65, 192 -> 63