An encryption to analyse

I wrote a cryption class, developed and altered over a period of time, and am wondering how it measures up. It was done completely independently, and I haven't actually read anything about encryption beyond learning how to use a binary file;).

So, comments would be appreciated. How good/bad is it? What could I do to improve it? etc.

Code:

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'Cryptor class module
'by me

Option Explicit

      Private Password As String 'The password for cryption
      Private Textstring As String 'The text to crypt
      Private TextString2 As String 'Stores existing textstring during initialization of a new password
      Private Threads() As Long 'A dynamic array that will contain the thread values
      Private TotalASCII As Long 'The ASCII value added to everything in the text, combined with the thread value
      Private ThreadNum As Long 'The number of cryption threads
      Private Chunk As String 'A chunk of data that is crypted by the Crypt subroutine

Private Sub Crypt()
      'This private subroutine does the actual cryption of chunks
              'of data fed to it by the CryptText or CryptFile methods
             
      Dim i As Long 'A counter
      Dim i2 As Long 'Another counter
      Dim TempChar As Long 'Temporary storage of ascii value
     
      i2 = 1
      For i = 1 To Len(Chunk) 'For each character in the chunk...
     
            'The new character's ASCII value will be that of the
                    'existing character logically Xored with the value
                    'of the current thread, then logically anded with
                    '255 to truncate it to the correct bit length for
                    'ASCII codes
              TempChar = ((Asc(Mid$(Chunk, i, 1))) Xor Threads(i2)) And 255
             
              'Write the new character to the chunk of data
              Mid$(Chunk, i, 1) = Chr(TempChar)
             
              'Increment the thread
              i2 = IIf(i2 = ThreadNum, 1, i2 + 1)
      Next i
End Sub
Public Sub CryptText()
          'This subroutine splits text into chunks for the Crypt method
         
      Dim i As Long 'A counter
      Dim Location As Long 'Stores the location in the textstring
      i = 1
     
      Do While i < (Len(Textstring) + 1)
              'While the end of the textstring hasn't yet been reached
              Select Case (Len(Textstring) - (Location - 1))
                    'Select case the length of the data left in the
                            'textstring to be crypted
                   
                    Case Is > 1048575
                            'If it is greater than one less than one megabyte
                           
                            'Grab a one megabyte long data chunk
                            Chunk = String(1048576, 0)
                            Chunk = Mid$(Textstring, i, 1048576)
                           
                            'Crypt the chunk
                            Crypt
                           
                            'Write the chunk back into the file
                            Mid$(Textstring, i, 1048576) = Chunk
                           
                            'Increment the location and the i counter
                            Location = Location + 1048576
                            i = Location
                           
                    Case Else
                            'If the remaining length is less than one megabyte
                           
                            'Get all of the remaining data and put it into chunk
                            Chunk = String((Len(Textstring) + 1 - Location), 0)
                            Chunk = Mid$(Textstring, i, (Len(Textstring) + 1 - Location))
                           
                            'Crypt chunk
                            Crypt
                           
                            'Write chunk back into the textstring
                            Mid$(Textstring, i, Len(Chunk)) = Chunk
                           
                            'End the loop since that was the last data
                            Exit Do
              End Select
        Loop
End Sub

Public Sub CryptFile(ByVal FilePath As String)
      'Similar to CryptText, but works with a file instead of a
              'string variable
             
      Dim i As Long 'A counter

      i = 1
      Open FilePath For Binary As #80 'Open the file
              Do While i < LOF(80) 'While the end of the file hasn't
                                                'been reached
                    Select Case (LOF(80) - (Loc(80) - 1))
                            'Select case the length of data left
                           
                            'If there is greated than or equal to
                                          'one megabyte
                            Case Is >= 1048576
                                 
                                  'Get a one megabyte chunk from the file
                                  Chunk = String(1048576, 0)
                                  Get #80, i, Chunk
                                 
                                  'Crypt the chunk
                                  Crypt
                                 
                                  'Write the chunk back into the file
                                  Put #80, i, Chunk
                                 
                                  'Increment i
                                  i = Loc(80) + 1
                                 
                            Case Else
                                  'If the remaining data is less than one
                                          'megabyte
                                         
                                  'Get the rest of the data
                                  Chunk = String((LOF(80) - (Loc(80))), 0)
                                  Get #80, i, Chunk
                                 
                                  'Crypt chunk
                                  Crypt
                                 
                                  'Write chunk back into file
                                  Put #80, i, Chunk
                                 
                                  'Exit loop since that was the last data
                                  Exit Do
                    End Select
              Loop
      Close #80
End Sub
Public Property Let CryptPassword(ByRef Pass As String)
      'This code occurs when a new password is given to Cryptor
     
      'Make sure it is within 4 to 64 characters
      Select Case Len(Pass)
              Case 4 To 128
              Case Else
                  MsgBox "Your password must be between 4 and 64 characters long.  It will later have a length 4 times that that the original had."
                  Exit Property
      End Select
     
      'Set the password
      Password = Pass
     
      'Initialize the cryption threads - run InitCrypt
      InitCrypt
     
      'Secure the password - run SecurePass
      SecurePass
End Property
Public Property Let TextToCrypt(ByRef Textstuff As String)
      'Allows the program to feed Cryptor the textstring
      Textstring = Textstuff
End Property
Public Property Get TextToCrypt() As String
      'Allows the program to get the text back after cryption
      TextToCrypt = Textstring
End Property
Private Sub InitCrypt()
      'Private sub to initialize the cryption threads
      Dim i As Long 'A counter
      Dim i2 As Long 'Temporary storage variable
     
      'Set TotalASCII and Threadnum to be 0 in case cryption
              'has already been run using a different password
      TotalASCII = 0
      ThreadNum = 0
     
      For i = 1 To Len(Password)
              'Add up all of the ASCII codes of each character in the
                    'password and a percentage value based on each
                    'character's position in the password
              i2 = i2 + ((Asc(Mid$(Password, i, 1))) * (10 + (i / 10)))
      Next i
      i2 = i2 \ 10
     
      'Store this value in TotalASCII
      TotalASCII = i2
     
      'The number of cryption threads is the TotalASCII divided
              'by 16, plus twice the length of the password
              '(which is 16 to 256 characters)
      ThreadNum = (TotalASCII \ 16) + (Len(Password) * 2)
     
      'Redimension the threads array
      ReDim Threads(1 To ThreadNum) As Long
     
      'i2 now equals TotalASCII divided by 4 divided by the length
              'of the password
      i2 = ((TotalASCII \ 4) \ Len(Password))
     
      For i = 1 To ThreadNum
              'Each thread equals is thread number times i2 times 7
                    'plus the TotalASCII, logically anded with 255
                    'to truncate it to 8 bits
              Threads(i) = ((i * i2 * 7) + TotalASCII) And 255
      Next i
End Sub
Private Sub SecurePass()
      'Private sub to secure the password
     
      'Backup the textstring
      TextString2 = Textstring
     
      PassCrypting 'Ensure that the password is secure by crypting/doubling it three times
      PassCrypting
      PassCrypting
             
      'Restore the original textstring
      Textstring = TextString2
End Sub
Private Sub PassCrypting()
      Textstring = Password & Password 'Textstring to crypt is the password twice
      CryptText 'Crypt the password
      Password = Textstring 'Return crypted value
      InitCrypt 'Re-initialize cryption threads again
End Sub

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So, to summarize use (so you don't have to figure out which thing happens first), you set a password. If you're crypting text, then you set the text, run the crypt routine, and retrieve it (am thinking I should just let the user pass the text when I next do some work on it). For a file, you set the password, and the run cryptfile, passing the filename. Encryption and decryption are the same, there's no difference to it.