Modern cryptography is designed to provide security assurances in an open communications environment. If our communication channel is so well-protected that eavesdroppers have no chance of manipulating or even just observing our messages, then cryptography is superfluous. Most of our communication channels, however, are hardly this well-guarded.

The backbone of communication in the modern world is a massive network of fiber optic cables. Making phone calls, viewing television, and browsing the web in a modern household generally relies on this network of fiber optic cables (a small percentage may rely purely on satelites). It is true that you might have different data connections in your home, such as coaxial cable, (asymmetric) digital subscriber line, and fiber optic cable. But, at least in the developed world, these different data mediums quickly join outside your house to a node in a massive network of fiber optic cables which connects the entire globe. Exceptions are some remote areas of the developed world, such as in the United States and Australia, where data traffic might still also travel substantial distances over traditional copper telephone wires.

It would be impossible to prevent potential attackers from physically accessing this network of cables and its supporting infrastructure. In fact, we already know that most of our data is intercepted by various national intelligence agencies at crucial intersections of the Internet.[7] This includes everything from Facebook messages to website addresses that you visit.

While surveilling data on a massive scale requires a powerful adversary, such as a national intelligence agency, attackers with only few resources can easily attempt to snoop at a more local scale. Though this can happen at the level of tapping wires, it is far easier just to intercept wireless communications.

Most of our local network data—whether in our homes, at the office, or in a café—now travels via radio waves to wireless access points on all-in-one routers, rather than through physical cables. So an attacker needs little resources to intercept any of your local traffic. This is particularly concerning as most people do very little to protect the data that travels across their local networks. In addition, potential attackers can also target our mobile broadband connections, such as 3G, 4G, and 5G. All these wireless communications are an easy target for attackers.

Hence, the idea of keeping communications secret by protecting the communication channel is a hopelessly delusional aspiration for much of the modern world. Everything we know warrants severe paranoia: you should always assume that someone is listening. And cryptography is the main tool we have to obtain any kind of security in this modern environment.

[7] See, for instance, Olga Khazan, “The creepy, long-standing practice of undersea cable tapping”, The Atlantic, July 16, 2013 (available at The Atlantic).