PQC, or post-quantum cryptography, is now part of the public discourse at numerous tech companies. Yet many in our industry still struggle to grasp its intricacies, and too few understand why moving to PQC is already necessary. Hence, let’s look at how to think about it and explore what it means for decision-makers today. To intelligently talk about post-quantum cryptography, we must lay down some fundamental principles about quantum computing, which means looking, even superficially, into quantum mechanics. The topic itself is highly complex and broad, so a blog post can’t even begin to scratch the surface. Hence, we simply aim to clarify some of the most basic principles in the hope of demystifying post-quantum cryptography.
The fundamental principles
What is quantum computing?
Classical computers store and process information using electrical signals, which can be in only two basic states: high or low voltage. Consequently, we represent these states using a binary language made of zeroes and ones. Everything a classical computer does, from the program it runs or the images and videos it displays, is ultimately a long string of these zeroes and ones. A quantum computer is similar in that it also uses a physical system as the foundation for all its calculations, but instead of using classical electrical signals, it uses quantum particles, such as electrons or photons. And these elements behave according to the laws of quantum mechanics.
One famous example of this is the double-slit experiment conducted by Thomas Young in the early 1800s. When light passes through two slits, it creates an interference pattern, as if it were a wave going through both slits at once. However, if one takes a measurement device to determine which slit the light goes through, the interference pattern disappears. In that instance, light behaves as if it were made of particles. This is what quantum mechanics calls the wave–particle duality. This behavior has been reproduced numerous times over the years with a variety of photons or matter, and it is one of the key ideas behind quantum computing.