decrypt

Very simple encryption example with VBScript

I previously mentioned a routine that I wrote to encrypt a string. Now, before the security folks look at the code… understand this:

This is intended only to obscure a string from a casual prying eye. It is NOT intended to be a replacement for true encryption like 3DES and RSA encryption. Please do NOT assume this routine is in any way secure or uncrackable. It is intended to only be an exercise in working with strings and is only as secure as the price you have paid for it. Nothing. Furthermore, it is provided as-is without warranties and by using it you agree that all risk from it’s use is transferred to you.

….Now that we’ve gotten the unpleasant legal disclaimer out of the way… Lets discuss the code!

Essentially, The code uses a variable length key to obscure the original string by iterating through the string you want obscured and adding the ASCII value of the character at each position of the original string with the ASCII value of a rotating “key character” in the key provided to generate a new ASCII value. This new ASCII value is then converted to a character and added to the newly encrypted string. The obscured string is further obscured by the fact that the original string is reversed prior to being changed. 

This key position changes after each character in the original string is obscured. The result is the key is iterated through sequentially as the original string is encrypted and when the end of the key string is encountered the iteration through the key string is started again from the beginning of the key string until the original string is completely encrypted.

This process works because the ASCII values in the typical string and the typical key string when added together do not exceed 255. (The highest possible ASCII character) Essentially, Strings and Keys with ASCII values higher than 126 should not be used or the result could be unpredictable– or worse yet, an unencryptable string.

Now that I’ve explained a bit about the premise… Lets look at the code!

Option Explicit

Dim temp, key

temp = “Now is the time for all good men To come To the aid of their fellow countrymen.”
key = “huasHIYhkasdho1″

temp = Encrypt(temp,key)
WScript.Echo temp
temp = Decrypt(temp,key)
WScript.Echo temp

Function encrypt(Str, key)
 Dim lenKey, KeyPos, LenStr, x, Newstr
 
 Newstr = “”
 lenKey = Len(key)
 KeyPos = 1
 LenStr = Len(Str)
 str = StrReverse(str)
 For x = 1 To LenStr
      Newstr = Newstr & chr(asc(Mid(str,x,1)) + Asc(Mid(key,KeyPos,1)))
      KeyPos = keypos+1
      If KeyPos > lenKey Then KeyPos = 1
 Next
 encrypt = Newstr
End Function

Function Decrypt(str,key)
 Dim lenKey, KeyPos, LenStr, x, Newstr
 
 Newstr = “”
 lenKey = Len(key)
 KeyPos = 1
 LenStr = Len(Str)
 
 str=StrReverse(str)
 For x = LenStr To 1 Step -1
      Newstr = Newstr & chr(asc(Mid(str,x,1)) - Asc(Mid(key,KeyPos,1)))
      KeyPos = KeyPos+1
      If KeyPos > lenKey Then KeyPos = 1
      Next
      Newstr=StrReverse(Newstr)
      Decrypt = Newstr
End Function