Re: Password for DBF

["Moisis Arturo Franco" <franco@eudoramail.com>]

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Dear Friend:

Perhaps I didn't understand the message very well, but if you want to protect the DBF file from being opened by another application, here is a little trick you can use.

DBF files, like the other ones, have a header at the very beggining of the file, This header contains very important information that allows application to determine how many records are inserted, what fields are in the table, and type information for each one of them.

What you cant do is encrypt the file's header (the first 2048 bytes of the file) with the XOR Function. Here's the Algorithm:

Function Encrypt(TextToEncript As String) as String
    Dim CountofChar as Integer   'Counter for iteration
    Dim CountOfEncr as Integer   'Counter for iteration on key
                                 'Because sometimes you need to
                                 'encrypt lager text than the key
                                 'is itself.

    Dim EncrypString$            'String that contains the key (pwd)
    Dim CharOriginal$            'Char extracted from the orig text.
    Dim CharEncripte$            'Char containing the encripted result
    Dim DestinString$            'Destination encrypted string

    'This is the key that you can use to encrypt the text
    'You have to keep it constant to deencrypt the text again
    EncrypString$ = "THIS IS THE PASSWORD"
    'Begin iteration to encrypt each char of the string until
    'It finishes
    CountOfEncr = 1
    For CountOfChar = 1 To Len(TextToEncript)
        'Extract The corresponding Char from the original string
        CharOriginal$(TextToEncript, CountOfChar, 1)
        'Extract The corresponding Char from the Encriptor string
        CharEncripte$(EncrypString$, CountOfEncr, 1)
        'Now that we have both chars, we are going to XOR them to
        'Obtain the corresponding encrypted char for that position.
        CharEncripte$ = Chr$(ASC(CharOriginal$) XOR ASC(CharOriginal$))
        'And finally, we concat that char to the dest encrypted string
        DestinString$ = DestinString$ + CharEncripte$
        'Now, we need to increment mannualy the counter of the next
        'character for the enncryption key. We also need to check if
        'the end of the key has been reached.
        If CountofEncr = Len(EncryptString$) Then
            CountOfEncr = 1
        Else
            CountOfEncr = CountOfEncr +1
        End If
    Next CountOfChar
    Encrypt = DestinString$

End Function

Well, that's all about the algorithm, now let's see what it does. Supose that you have a char that you want to encrypt, an "A" for example. And your password is a "B" then XOR does do following:

    Binary Code for "A"  01000001  (65 Dec.)
    Binary Code for "B"  01000010  (66 Dec.)
    XOR Opperation       --------
    XOR RESULT --------->00000011 A TOTALLY DIFFERENT CHAR CODE THAN
                                  THE ORIGINAL "A"

Now, here comes the deencryption part. To do this you just simply use another XOR on the encrypted char. using the same key:

    Encrypted Char 03    00000011
    Bynare code for "B"  01000010
    XOR Opperation       --------
    XOR Result --------->01000001 "A" Now we have the original char 
                                  again.

So, the algorithm above, does this, but with strings. Perhaps you might consider this a little bit simple, but if you hold the key as a constant in your code, it will be hard to decipher, since once you compiled the code, no one will be able to see the key.

I hope this humble idea helps!

Moisis Franco


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