National Quantum Day: A Bluffers Guide to PQC

Yesterday was National Quantum Day, and which aimed to increase awareness of the rise of quantum computers. One of the most significant impacts of quantum computers will be on the cracking of public key encryption. This will have an impact in three areas: key exchange, public key encryption, and digital signatures. With TLS, for example, we will have to replace ECDH for key exchange and RSA/ECDSA for digital signatures. Basically, the key exchange part negotiates an end-to-end session key for an encrypted tunnel, while the digital signature part verifies the server that you connect to. Without public key encryption, our conversions on Web would not be private, and where we could not trust anything.

Key exchange

For key exchange, there is only one standard just now for PQC key exchange, and that is Kyber (a lattice-based method). Overall, Kyber is not quite a key exchange method, and is basically a KEM (Key Encapsulation Mechanism). There are other methods, such as McEliece, but these are yet to be approved as a standard.

With KEM, if Bob wants to pass a symmetric key to Alice, he encapsulates (“encrypts”) with his public key, and she decrypts this with his private key: