Understanding hashing algorithms in VBA and how to avoid collisions.

[kelly mort]

I found this code at stackoverflow.com and I am falling in love with the code. I am now learning about the hashing algorithms in VBA and I wish someone with a deeper understanding could help guide me and advise me on a few things:
1. Is there a possibility that two or more different strings or input will produce same output?
2. If the above can occur, is there a way to prevent that and how?

Sub tester()
    Dim myInput$
    myInput = "money"
    'MsgBox hash4(myInput)
    MsgBox hash12(myInput)
End Sub


Function hash12(s$)
    Dim l%, l3%, s1$, s2$, s3$
    l = Len(s)
    l3 = Int(l / 3)
    s1 = Mid(s, 1, l3)
    s2 = Mid(s, l3 + 1, l3)
    s3 = Mid(s, 2 * l3 + 1)
    hash12 = hash4(s1) + hash4(s2) + hash4(s3)
End Function

Function hash4(txt)
    Dim x&, mask, i, j, nC, crc%, c$
    crc = &HFFFF
    For nC = 1 To Len(txt)
        j = Asc(Mid(txt, nC))
        crc = crc Xor j
        For j = 1 To 8
            mask = 0
            If crc / 2 <> Int(crc / 2) Then mask = &HA001
            crc = Int(crc / 2) And &H7FFF: crc = crc Xor mask
        Next j
    Next nC
    
    c = Hex$(crc)

    While Len(c) < 4
      c = "0" & c
    Wend
    
    hash4 = c
End Function

 

[Marc L]

• First, I used once a simple numeric hash from the common Dictionary library :

Sub DemoNumHash()
    With CreateObject("Scripting.Dictionary")
        MsgBox .HashVal("money") & vbLf & vbLf & .HashVal("asdf")
    End With
End Sub

• For crypto it depends on what you exactly need, if you use worksheet cells to store encrypted data, …

 

[kelly mort]

Cool.

I have a question though:

money is giving out 298 while asdf is giving out 1173 - why is it so?
What is actually taking place inside the code?

 

[Dermot]

Okay you can share it for me to have a look. I love to learn new things.

Kelly, I like hashing and encryption too.

It's not something that can be covered properly in this forum, but if you google those terms, there are thousands of videos and webpages explaining how they work, and which are most reliable and secure. After that, when you are ready to use some code, I would google,
VB hash or
VB encryption
and you will get both VB (Visual Basic) and VBA code. VB code is very similar (but ignore VB.Net code, that is very different)

Then it's a case of trying it out. You may have to google more to get things working, but if you're keen, you'll get there.

 

[kelly mort]

Thanks @Dermot.

I will do exactly that.

 

[Marc L]

money is giving out 298 while asdf is giving out 1173 - why is it so?

It's the way it works, maybe more like a SRC than a hashing algorhithm …​

​

Maybe I have some hashing way but I have to first inspect if it can be converted and without being too slow under VBA …​

 

[Marc L]

​

In fact I wanna know what you really need : some 'one way encryption' hashing algorithm which can not be decrypted​

or a 'two way encryption' more like a cryptography algorithm ? And an answer to my post #11 …​

 

[kelly mort]

​

In fact I wanna know what you really need : some 'one way encryption' hashing algorithm which can not be decrypted​

or a 'two way encryption' more like a cryptography algorithm ? And an answer to my post #11 …​

What I really need is to understand how things work out with the hashing and/or cryptography algorithms.

I am new to these stuffs so I can't tell for sure whether I needed A or B.

So maybe the two examples would help.

 

[Marc L]

​

Easy to understand : each character is transformed to another one through an algorithm …​