Homomorphic Encryption

Overview

Homomorphic encryption is a cryptographic technique that allows selected computations to be performed on encrypted data without first exposing the underlying plaintext to the computing party.

Homomorphic Encryption is closely connected to Privacy-Preserving Analytics, Re-identification Risk, and Privacy Risk Assessment. It differs from ordinary encryption at rest because ordinary encryption generally requires decryption before processing, while homomorphic schemes preserve a mathematically meaningful relationship through computation.

Operational implementation should select a scheme and security level appropriate to the calculation, protect keys, validate implementations, measure accuracy and performance, minimize plaintext exposure, and document residual leakage.

The principal failure modes include incorrect parameter selection, excessive computational cost, implementation flaws, side channels, key compromise, output leakage, and claims of privacy that exceed the actual threat model.

Useful measures include encrypted workload coverage, latency overhead, key rotation status, failed computation rate, and privacy tests against defined attackers.

Operationally, teams should select a scheme and security level appropriate to the calculation, protect keys, validate implementations, and measure accuracy and performance. Key risks include incorrect parameter selection, excessive computational cost, implementation flaws, and side channels.

A production treatment of Homomorphic Encryption should test a cryptographic technique that allows selected computations to be performed on encrypted data without first exposing the underlying plaintext to the computing party within the relevant asset, decision, or service state. The Homomorphic Encryption context record for a cryptographic technique that allows selected should preserve source data, configuration or policy version, responsible actor, exception, and outcome. Review of Homomorphic Encryption should determine whether safeguards addressing a cryptographic technique that allows selected changed exposure in practice, not merely whether a document or setting existed.