cryptography - How to predict the next GUID from a given GUID?

Question

I have sent 10000 mails to our customers and each mail had a link of the format

http://example.com/LogIn?key={guid}

Unfortunately the guid I sent were random guids (test data generated by Guid.NewGuid()) so the customers have all received invalid links...

Based on the 404s i receive from the webserver I have a few guids that I sent out. I have read that the guid generator in windows is weak so you can predict the next guid from one you already have. Does anyone know how? If i could do that I could make the guids I sent out valid so the links would work again.

Answer 1

The way Windows has generated GUIDs has changed several times, and lots of seemingly reliable advice on the internet is completely wrong (maybe just out of date, maybe always completely wrong).

The last time I looked into this (a few years ago, probably XP SP2), I stepped right down into the OS code to see what was actually happening, and it was generating a random number with the secure random number generator.

I doubt you'll have much luck predicting one GUID from another if you generated them in the default way.