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Class: Encryption in Category General VBA/VB6 : Encryption and Compression from Total Visual SourceBook

Encrypt and decrypt files and strings with Unicode support using XOR password encryption in VBA and VB6.

The password is also encrypted as the string or file is processed, providing an additional level of security. For simple string encryption, consider using modEncryption instead.

Procedure List

Procedure Name	Type	Description
(Declarations)	Declarations	Declarations and private variables for the CEncryption class.
InputFileName	Property	Get the name of the input file.
OutputFileName	Property	Get the name of the output file.
Password	Property	Get the password.
Class_Initialize	Initialize	Set initial values to defaults which may be overridden with property settings.
EncryptFile	Method	Encrypt the file specified in m_strInputFileName to the file specified in m_strOutputFileName. This procedure uses buffered file reads and writes for better performance. The encrypted file produced by the method is reversible. This means that if you encrypt a file, reverse the InputFileName and OutputFileName properties, and call this method again, the original file is restored. Note: The same password must be supplied to successfully decrypt the file. This method also raises an event called file progress. This event can be used to track the progress of the file being processed. See the example tab for an example of how to use this event. This method also uses a file buffer. Using a file buffer significantly speeds up the performance of this method.
EncryptString	Method	Encrypt/Decrypt the passed string with XOR encryption. The encrypted string produced by the method is reversible. This means that if you encrypt a string, then encrypt the results of that operation, the original string is restored. Note: The same password must be supplied to successfully decrypt the string. See the example tab for a demonstration of this. If you need an ASCII version of this function, use the EncryptStringAscii method.
EncryptStringAscii	Method	Encrypt/Decrypt the passed string with XOR encryption, returning the result in ASCII format. The encrypted string produced by the method is reversible. This means that if you encrypt a string, then encrypt the results of that operation, the original string is restored. Note: The same password must be supplied to successfully decrypt the string. See the example tab for a demonstration of this. The EncryptStringAscii method returns the result in ASCII format. If you need to pass the results of the EncryptString function on the command line, or use it external to your program, it is recommended that you use the ASCII version of this function.
EncryptByte	Private	Encrypt one byte, and modify the password. Modifying the password as we encrypt makes the encryption slightly harder to break.
ReadFile	Private	Read the specified number of bytes from the file. This function significantly increases the speed of processing files. The alternative to using a file buffer is reading a byte at a time from the file.

Example Code for Using Class: Encryption

' Example of CEncryption
'
' To try this example, do the following:
' 1. Create a new form
' 2. Create a command button named 'cmdTest'
' 3. Paste all the code from this example to the new form's module.
' 4. Run the form

' This example assumes that the sample files are located in the folder named by the following constant.
Private Const mcstrSamplePath As String = "C:\TVSBSamp"

Private WithEvents mclsEncryption As CEncryption

Private Sub cmdTest_Click()
  ' Comments: Examples of encrypting and unencrypting files and strings

  Const cstrOriginal As String = mcstrSamplePath & "\sample.txt"
  Const cstrEncrypt As String = mcstrSamplePath & "\encrypt.enc"
  Const cstrDecrypt As String = mcstrSamplePath & "\deencrypt.txt"
  Const cstrExample As String = "One small step for [a] man; one giant leap for mankind"

  Dim dblCompressionRatio As Double
  Dim strString As String

  ' Initialize class
  Set mclsEncryption = New CEncryption

  mclsEncryption.Password = "password"

  ' Example of encrypting a file
  mclsEncryption.InputFileName = cstrOriginal
  mclsEncryption.OutputFileName = cstrEncrypt
  mclsEncryption.EncryptFile

  ' Display the size change with encryption achieved
  dblCompressionRatio = FileLen(cstrEncrypt) / FileLen(cstrOriginal)
  MsgBox "File is " & Format$(dblCompressionRatio, "Percent") & " of its original size"

  ' Decrypt the file into a new one. Notice the same EncryptFile procedure is used to convert the encrypted file back to its unencrypted state.
  mclsEncryption.InputFileName = cstrEncrypt
  mclsEncryption.OutputFileName = cstrDecrypt
  mclsEncryption.EncryptFile
  MsgBox cstrDecrypt & " created by decrypting " & cstrEncrypt

  ' Example of Unicode encrypting and decrypting strings. Results in the Immediate Window.
  Debug.Print "Original String: " & cstrExample

  strString = mclsEncryption.EncryptString(cstrExample)
  Debug.Print "Encrypted String: " & strString

  strString = mclsEncryption.EncryptString(strString)
  Debug.Print "Un-Encrypted String: " & strString

  ' Example of ASCII encrypting and decrypting strings. Results in the Immediate Window.
  strString = mclsEncryption.EncryptStringAscii(cstrExample)
  Debug.Print "ASCII Encrypted String: " & strString

  strString = mclsEncryption.EncryptStringAscii(strString)
  Debug.Print "ASCII Un-Encrypted String: " & strString

  Set mclsEncryption = Nothing

End Sub

Private Sub mclsEncryption_FileProgress(dblPercentage As Double)
  ' Comments: This procedure captures the Progress Event and reveals the percentage completion for the file that's being compressed
  '           This example puts the information on the Immediate Window. You could show the information on a form as text or display a graphic.
  ' Params  : dblPercentage       Percent of completion between 0 and 1

  Debug.Print "Percent done: " & Format$(dblPercentage, "Percent")
End Sub

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