Quantum Computers Are Not a Threat to 128-bit Symmetric Keys

A detailed technical argument that AES-128 and other 128-bit symmetric keys remain secure against quantum computers, debunking the common misconception that Grover's algorithm halves symmetric key security. The key insight is that Grover's algorithm cannot be efficiently parallelized — splitting the search space across multiple quantum computers degrades the quadratic speedup, making a practical attack on AES-128 require 140 trillion quantum circuits running in parallel for a decade. This is 430 sextillion times more expensive than breaking 256-bit elliptic curves with Shor's algorithm. NIST, BSI, and academic experts all agree: no symmetric key sizes need to change as part of the post-quantum transition. The post also argues against unnecessary migration to 256-bit symmetric keys, warning it wastes resources needed for the genuinely urgent asymmetric cryptography transition.