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Security Fundamentals & Crypto · Advanced

Homomorphic Encryption

Encryption that allows computation on ciphertext, producing encrypted results that decrypt to the correct answer.

Definition

Fully homomorphic encryption (FHE) supports arbitrary computation on encrypted data, while partially homomorphic schemes support only addition or multiplication. It protects data in use in untrusted environments such as the cloud. Performance overhead remains high, though libraries like Microsoft SEAL and OpenFHE are maturing.

Example

A cloud service sums encrypted salaries and returns an encrypted total that only the HR department can decrypt.

Exam tip

Homomorphic encryption protects data in use without decrypting it.

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