Often time we use query string collection to retrieve an unique record from a table. Notice the following
piece of code -
Detail.asp?RecordID=200
Here we are passing a query string value called "RecordID" using the url. We then use the Query String
collection "RecordID" to get the actual number -
<%
Dim RecordID
RecordID = Request.QueryString("RecordID")
%>
The problem with the above method is that we are exposing "RecordID" to the public. Hence making easy to
hackers to just change the RecordID Query string to retrieve other values of the table.
Solution to the above problem
In order to solve the above problem, we will use two ASP pages and the ASP random number function to
scramble the passing query string value so that the real record number is not exposed to others.
On the first page we get a random number with the following code -
<%
Randomize timer
‘’ Randomizing the timer function
rndNum = abs(int((rnd() * 3001)))
‘’ To generate a prime based, non-negative random number..
rndNum = rndNum + 53
Session("rndNum") = rndNum
‘’We place the random number value in a session variable so that we can use it again in the next page %>
Now that we have our random number we will scramble our query string with it! Here is how -
<%
‘’Assuming you have a record set retrieved -
Display_Rs.movefirst
While not Display_Rs.Eof
Response.Write "<a href=detail.asp?RecordID="
Response.Write (Display_Rs("RecordID")*rndNum)
‘’ Notice we are multiplying the actual record number with the random number to scramble the query ‘’string
Response.Write Display_Rs("RecordID") & "</a>"
Display_Rs.Movenext
Wend
%>
In the next page we will un-scramble the query string! Here is how -
<%
Dim RecordID
RecordID = request.querystring("RecordID")/Session("rndNum")
‘’ We are dividing the record ID query string value with the same formula to un-scramble and pass the
actual record ID to the SQL statement
Session.abandon
‘’ Releasing Session value for the next record
%>
That‘’s it! Using the above method you can scramble a query string as much as you like. For example
multiply the random number with a very complex formula to generate an even more difficult integer number.
The key point here is you divide the number with the same formula yielding to the original value. This
technique is not full proof but much more difficult to break in that passing a regular query string value.
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