DigiNotar was a Dutch certificate authority owned by VASCO Data Security International, Inc.[1][2] On September 3, 2011, after it had become clear that a security breach had resulted in the fraudulent issuing of certificates, the Dutch government took over operational management of DigiNotar's systems.[3]

The answer, of course, is end-to-end encryption. The way this works is to remove any “man-in-the-middle” vulnerabilities by encrypting messages from endpoint to endpoint, with only the sender and recipient holding the decryption key. This level of messaging security was pushed into the mass-market by WhatsApp, and has now become a standard feature of every other decent platform.

The issue, though—and it’s a big one, is that the SMS infrastructure is inherently insecure, lending itself to so-called “man-in-the-middle attacks.” Messages run through network data centres, everything can be seen—security is basic at best, and you are vulnerable to local carrier interception when travelling.

When you make a call using Signal, it will generate a two-word secret code on both the profiles. You will speak the first word and the recipient will check it. Then he will speak the second word and you can check it on your end. If both the words match, the call has not been intercepted and connected to the correct profile