# What is Homomorphic Encryption?

> Homomorphic encryption is cryptography that allows specified computations to be performed on encrypted data without first exposing its plaintext.

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## Content

When an authorized party later decrypts the resulting ciphertext, the plaintext corresponds to the intended computation. This can reduce the need to reveal input data to the system performing an outsourced or shared calculation.

Schemes differ substantially. Some support only particular operations, leveled schemes support bounded computation, and fully homomorphic encryption (FHE) can evaluate arbitrary circuits within its model. Exact and approximate schemes also have different correctness and numerical behavior, so a useful deployment starts with a precise workload, threat model, and accuracy requirement.

### Key points

- **Scheme and workload:** Match supported operations, data encoding, multiplicative depth, precision, batching, and output requirements to the actual computation rather than treating all homomorphic schemes as interchangeable.
- **Parameters and keys:** Select reviewed parameters for the required security level, manage evaluation and decryption keys carefully, and account for ciphertext expansion, noise growth, and any bootstrapping.
- **Deployment:** Benchmark representative data and queries, minimize exposed metadata, restrict who can submit computations, and integrate authorization, auditing, key recovery, and result handling.
- **Important limitation:** Homomorphic encryption can be computationally and operationally expensive. It does not inherently prove that the requested computation was performed correctly, hide every access pattern or metadata field, protect compromised key holders or endpoints, or make unsafe input and output handling secure.

### Related terms

[Encryption](<https://yellowcube.eu/glossary/encryption/>) · [Confidential computing](<https://yellowcube.eu/glossary/confidential-computing/>) · [Data protection](<https://yellowcube.eu/glossary/data-protection/>) · [Cryptography](<https://yellowcube.eu/glossary/cryptography/>) · [Data privacy](<https://yellowcube.eu/glossary/data-privacy/>)

### Sources

[NIST, Fully Homomorphic Encryption](https://csrc.nist.gov/projects/pec/fhe) · [ISO/IEC 18033-6:2019, Encryption algorithms — Part 6: Homomorphic encryption](https://www.iso.org/standard/67740.html) · [HomomorphicEncryption.org, Security Guidelines](https://homomorphicencryption.org/security-guidelines/)

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