Simple encryption in VB

This is an simple introduction on write your own encryption functions, but as stated these function are very simple, so do NOT use this function for encrypting any important data.

The first and very simple encryption:
The following function adds the code number to the ascii value of the text, which all characters change to something else.
An output of this function could be:
Rovvy8*^ro*}zkwwo|*lovy�*s}*os~ro|*}sxq*ƒy|*|o}y|mo}*~y*}oxn*y~*lvu
x}yvsms~on*mywwo|mskv*o7wksv*2,}zkw,3*y|*s}*nomoz~s€ovƒ*~|ƒsxq*~y*wkuo*s~
vyyu*vsuo*ro*s}8*Sx*os~ro|*mk}o6*k*voqs~swk~o*mywzkxƒ*vsuo*ƒy|}
*z|ylklvƒ�yvn*xy~*kzz|y€
o8*^ro*sxpy|wk~syx*lovy�*}ryvn*lo*kvv*ƒy*xoon8
Quite hard to read, isn't it?

Public Function Encrypt1(Txt As String, CodeNr As Integer) As String Dim i As Long Dim Out As String 'Inital output value is empty string Out = "" 'Change ASCII codes For i = 1 To Len(Txt) Out = Out & Chr(Asc(Mid$(Txt, i, 1)) + CodeNr) Next i Encrypt1 = Out End Function

As encryption en decryption are not that different we just call Encrypt1 from the decryption function:

Public Function Decrypt1(Txt As String, CodeNr As Integer) As String 'Decryption is the same as encryption with CodeNr*-1 Decrypt1 = Encrypt1(Txt, CodeNr * -1) End Function

Now you may be wondering why this code is so extremely weak. But it's actually quite simple, as the most commonly used character would normally be the space. Below the code to break this code easily:

Function BreakCode(CText as String) as String Dim a(0 To 255) As Long Dim Txt As String Dim ascii As Byte Dim l As Byte Dim q As Long Dim SugCodeNr As Integer 'Count how often characters occur Txt = CText l = 0 For q = 1 To Len(Txt) ascii = Asc(Mid$(Txt, q, 1)) a(ascii) = a(ascii) + 1 If a(ascii) > a(l) Then l = ascii Next q Debug.Print "Most used character: '" & Chr(l) & "'" 'Space (ascii 32) is most often used in texts 'As we now this we can calculate the CodeNr... SugCodeNr = l - 32 BreakCode = Decrypt1(Txt, SugCodeNr) Debug.Print "Code number = " & CStr(SugCodeNr) End function