Quantum computers pose the greatest threat to asymmetric cryptographic algorithms.
This means the cryptographic system used to digitally sign certificates and handle the initial SSL/TLS handshake are both potential attack vectors if you use asymmetric keys.
NIST and ASC X9 assert that symmetric cryptographic algorithms used to create the session keys for securing data in transit after the initial TLS/SSL handshake, appear to be resistant to quantum computer attacks.
In fact, doubling the bit length of a symmetric key seems to be enough to protect against quantum computer attacks.
We’ve seen this before with the NSA and NIST endorsing 3-DES. Like 3-DES and DES, the Data Encryption Standard was broken and we’re left with the AES cryptographic algorithms.
This is because symmetric keys are based on a pseudo-random string of characters and would require the use of a brute force attack or exploiting a known vulnerability to break the encryption, as opposed to using an algorithm (e.g., Shor’s algorithm) to break asymmetric cryptography.
