Homomorphic encryption is a cryptographic technique that lets a system perform calculations on ciphertext and produce an encrypted result that, once decrypted, matches the computation on the original plaintext. In simple terms, the server can process data without learning what the data is. Variants range from partially homomorphic schemes, which support limited operations, to fully homomorphic encryption, which supports general computation but at a much higher cost.
It matters because it enables privacy-preserving cloud services, secure analytics, and encrypted AI inference. In defense, it reduces exposure of sensitive records to infrastructure operators. In attacks, the weak point is often not the math but the implementation: bad parameter choices, side-channel leakage, malformed ciphertext handling, or a compromised endpoint can still expose data or break correctness. Homomorphic encryption protects content, but it does not eliminate the need for secure engineering.