Grover's algorithm is the second major quantum attack vector (after Shor's algorithm). While Shor's completely breaks public-key cryptography, Grover's provides a quadratic speedup against symmetric encryption and hash functions — effectively halving their security level.
Impact on cryptography:
- AES-128 → 64-bit security (breakable)
- AES-256 → 128-bit security (still secure)
- SHA-256 → 128-bit collision resistance (still secure)
- SHA-128 → 64-bit collision resistance (breakable)
Why Grover's is less threatening than Shor's: Grover's only provides a quadratic speedup, not an exponential one. Doubling key lengths neutralizes it completely. This is why AES-256 and SHA-256 remain quantum-safe — they were already designed with enough security margin.
BMIC's defense: BMIC uses AES-256-PQC (maintaining 128-bit post-quantum security) and SHA-256 hashing throughout its protocol. These choices ensure Grover's algorithm cannot meaningfully weaken BMIC's symmetric cryptography.