You may even have heard of quantum cryptography which makes use of quantum computers and quantum mechanical effects.
Post-quantum cryptography isnt supposed to be the next biggest thing after quantum encryption.
Instead, its the class of cryptography that is still relevant in a world where powerful quantum computers exist.
These problems have been carefully chosen because they are extremely difficult unless you know specific information.
Even with computers, these math problems are provably difficult.
In 2019 a study spent 900 CPU core years to break a 795-bit RSA key.
A 1024-bit RSA key would take more than 500 times more processing power to break.
The problem is that quantum computers work in a completely different way compared to normal computers.
Unfortunately, many of the math problems used in cryptography are perfect examples of this.
Traditionally, if you want to increase the security of encryption, you just need longer keys.
The whole game is up and a new system is needed.
The effective security of an asymmetric cipher like RSA is decreased by the square root.
A 2048-bit RSA key offers the equivalent of 45 or so bits of security against a quantum computer.
For symmetric algorithms like AES, the effective security is only halved.
This is weak enough to be considered insecure.
The problem can be solved, however, by doubling the key size to 256 bits.
A 256-bit AES key offers 128-bits of protection even against a sufficiently powerful quantum computer.
That is enough to be considered secure.
Even better, 256-bit AES is already publicly available and in use.
Tip: The bits of security offered by symmetric and asymmetric encryption algorithms are not directly comparable.
The whole sufficiently powerful quantum computer thing is a bit hard to define precisely.
The key fact is that no one has the technology to do this yet.
The problem is we dont know when someone will develop that technology.
It could be five years, ten years, or more.
There are actually many proposed encryption schemes that are safe to use even in the face of quantum computers.
The challenge is to standardise these post-quantum encryption schemes and prove their security.
Conclusion
Post-quantum cryptography refers to cryptography that remains strong even in the face of powerful quantum computers.
Quantum computers are able to thoroughly break some types of encryption.
They can do so far faster than normal computers can, thanks to Shors algorithm.
The speed-up is so great that there is no way to practically counter it.
Many post-quantum cryptography candidates are essentially ready to go.
A lot of research is ongoing to identify the best options for widespread use.
A key thing to understand is that post-quantum cryptography runs on a normal computer.
This differentiates it from quantum cryptography which needs to run on a quantum computer.
