• Home
 · 
• Encryption
 · 
• File encryption procedure.

File encryption procedure.

File encryption procedure.

Rate File encryption procedure.

• 1
• 2
• 3
• 4
• 5

(2(2 Vote))

'// Call cipher(filename, password)
'// Used on its own, the procedure will both encrypt and decrypt.
'// Use in conjunction with your own bit rotation and/or compression routines to
'// increase security.
'// This is not that fast, so best to use it only for small files (250k max) although
'// it will encrypt anysize file.
'// If anyone knows how to speed encryption up, please let me in on it.
'// Also, if anyone knows how to implement the fibinachi sequence without the numbers
'// getting so big that VB crashes, please let me in on that too.
'// [email protected] - http://members.tripod.co.uk/chillsdon

Private Sub cipher(filespec As String, strPwda As String)

    Dim mybit As String * 1
    Dim strPwd As String
    Dim tmp1 As String, tmp2 As String, tmp3 As String, tmp4 As String
    
    '// initialize variables
    mybit = String(1, " ")
    strPwd = ""
    tmp1 = ""
    tmp2 = ""
    tmp3 = ""
    tmp4 = ""
    
    '// make password bigger and a little psuedo random
    '// e.g. "password" becomes "PASSWORDpAsSwOrDpasswordPaSsWoRd"
    tmp1 = UCase(strPwda)
    tmp2 = LCase(strPwda)
    For z = 1 To Len(strPwda)
        If z Mod 2 = 0 Then
            k = UCase(Mid(strPwda, z, 1))
            j = LCase(Mid(strPwda, z, 1))
        Else
            k = LCase(Mid(strPwda, z, 1))
            j = UCase(Mid(strPwda, z, 1))
        End If
        tmp3 = tmp3 & k
        tmp4 = tmp4 & j
    Next z
    strPwda = tmp1 & tmp3 & tmp2 & tmp4
    
    '// encrypt the password with itself
    For i = 1 To Len(strPwda)
        strPwd = strPwd & Chr(Asc(Mid(strPwda, i, 1)) Xor Asc(Mid(strPwda, (i Mod Len(strPwda)) + 1, 1)) And &HFF)
    Next i
    
    filelength = FileLen(filespec)
    Open filespec For Binary As #1

    '// encrypt file with encrypted password
    For i = 1 To filelength
        Get #1, i, mybit
        mybit = Chr(Asc(mybit) Xor Asc(Mid(strPwd, (i Mod Len(strPwd)) + 1, 1)) And &HFF)
        Put #1, i, mybit
        
        '// percent_done equals just that, attach it to a progress bar
        percent_done = Format((i / (filelength / 100)), "0.00")
    Next i
    
    Close #1
    
End Sub