Post Quantum Cryptography
The SSL/TLS protocol uses RSA, Diffie-Hellman (DH) or Elliptic Curve Diffie-Hellman (ECDH) primitives for the key exchange algorithm.
RSA is based on the fact that when given a product of two large prime numbers, factorizing the product (which is the public key) is computationally intensive, but a quantum computer could efficiently solve this problem using Shor’s algorithm. Similarly, DH and ECDH key exchanges could all be broken very easily using sufficiently large quantum computers.
For symmetric ciphers, the story is slightly different. It has been proven that applying Grover’s algorithm the strength of symmetric key lengths are effectively halved: AES-256 would have the same security against an attack using Grover’s algorithm that AES-128 has against classical brute-force search. Hashes are also affected in the same way symmetric algorithms are.
Therefore, we need new algorithms which are more resistant to quantum computations. This article introduces you to 5 proposals, which are under study.