PQC Weak Key Length (Symmetric/Hash Strength Below the Post-Quantum Baseline)

Flags symmetric ciphers and hash functions whose key or digest size is adequate against a classical attacker today but below the post-quantum baseline. This is the Grover axis of post-quantum readiness, distinct from pqc_readiness (the Shor axis — public-key algorithms that no key-size increase can save) and from insufficient_key_size (sizes that are already weak against classical attackers).

Grover’s algorithm gives a quadratic speed-up to brute-force search, halving the effective security of a symmetric key: AES-128 drops to ~64-bit effective strength, and a hash’s preimage resistance is similarly reduced. Such algorithms are perfectly safe against today’s classical computers but are not post-quantum ready. NSA’s CNSA 2.0 suite and NIST guidance therefore require AES-256 for symmetric encryption and SHA-384 / SHA-512 (or SHA3-384+) for hashing.

Only algorithms that are classically acceptable today are reported here; classically broken or deprecated primitives (DES, RC4, MD5, SHA-1) are reported by the weak-cipher / weak-hash detectors so the same usage is not flagged twice with conflicting advice. For symmetric ciphers, a finding requires an explicitly stated key size so a bare family reference sized elsewhere is not falsely flagged.

The post-quantum baselines are configurable via the minPqcStrength property (e.g. symmetric/256, hash/384) so the thresholds can be adapted to an organization’s own standard.

In Kotlin, the algorithm is named at the JCA factory; a SHA-256 digest is fine today but not post-quantum ready, whereas SHA-384/512 are:

Raise the parameter to the post-quantum baseline: use AES-256 for symmetric encryption and SHA-384 / SHA-512 (or SHA3-384+) for hashing. Unlike public-key algorithms on the Shor axis, no migration to a new algorithm family is required — the existing primitive is hardened in place by doubling its size.