PET Compass

Review status

Last reviewed: 2026-06-02 Evidence level: Expert judgment Snapshot scope: Starter decision guidance. Cost, maturity, and tooling claims need stronger sourced evidence before production use.

The PET Compass helps you choose a short list of candidate technologies before designing an architecture.

For the project's evidence standard, see Evidence Policy. For claims that need sourcing or measurement, see Claim Register.

Decision Inputs

Question	Why It Matters
Can raw data move?	Determines whether centralization, federated learning, MPC, HE, TEEs, or clean rooms are realistic.
Is a formal privacy guarantee required?	Differential privacy may be necessary, either alone or in composition.
What output is allowed?	Protected inputs do not prevent output leakage.
Who is the adversary?	Honest-but-curious, malicious, colluding, and external attackers require different controls.
Is hardware trust acceptable?	TEEs are practical when hardware and attestation are acceptable assumptions.
What latency and cost are tolerable?	HE and MPC may be excellent but too expensive for some workloads.

Starter Recommendation Matrix

Constraint	Start With	Often Combine With
Data cannot move	FL, MPC, HE, TEE, clean room	Secure aggregation, DP, auditing
Formal individual privacy is required	DP	FL, synthetic data, clean rooms
Encrypted inference is required	HE	TEE for hybrid designs, model compression
Hardware trust is acceptable	TEE	DP, audit logs, policy controls
Aggregate measurement is needed	Federated analytics, clean room, MPC	DP thresholds, output review
Safer sharing is needed	Synthetic data	DP, privacy auditing, utility tests

Do Not Stop At The Matrix

The matrix produces candidates, not an architecture. After choosing a candidate PET, move to patterns and threat models.

Before committing to a design, collect evidence for the target workload: expected latency, utility, privacy guarantee, adversary model, deployment complexity, and output leakage.