"On the other hand, symmetric algorithms such as AES are believed to be immune to Shor. In most cases, the best-known quantum key recovery attack uses
Grover’s algorithm which provides a generic square-root speed-up over classical
exhaustion in terms of the number of queries to the symmetric algorithm. In other
words, Grover would recover the 256-bit key for AES-256 with around 2^128 quantum
queries to AES compared to around 2^256 classical queries for exhaustion.
"
