Question

I am in the process of creating an app in which a customer can add email addresses to an event. This means that each email address is sent 2 urls via email when added to the list, 1 url to accept and the other to decline. The url is made up of a number of query parmatters, id’s etc.

The issue I have is that I want to prevent the scenario in which someone could “guess” another persons url – as such guest the combination of parametters etc. While this is very unlikely, I still want to prevent such.

I have seen several scenarios to help prevent this, ie. add a hash value, encrypt the url etc. However I am looking for the most secure and best practise approach to this and would like any possible feedback.

As an aside I am coding in C# but I dont believe the solution to this is language specific.

Thanks in advance.

Answer 1

I agree this is not language specific. I had a situation very similar to this within the last few years. It needed to be extremely secure due to children and parents receiving the communications. The fastest solution was something like the following:

1. First store the information that you would use in the URL as parameters somewhere in a database. This should be relatively quick and simple.
2. Create two GUIDs.
3. Associate the first GUID with the data in the database that you would have used for processing an “acceptance”.
4. Associate the second GUID for a “decline” record in the database.
5. Create the two URL’s with only the GUID’s as parameters.
6. If the Acceptance URL is clicked, use the database data associated with it to process the acceptance.
7. If the Decline is clicked, delete the data out of the database, or archive it, or whatever.
8. After a timeframe, is no URL is clicked, delete or archive the data associated with those GUID’s so that they can no longer be used.

GUID’s are extremely hard to guess, and the likelihood of guessing one that is actually usable would be so unlikely it is nearly impossible.