Fully Homomorphic Encryption and the Dawn of a Truly Private Internet

Summary

Fully Homomorphic Encryption and the Dawn of A Truly Private Internet 2025-07-16 fhe programming essay gene-spafford "Using encryption on the Internet is the equivalent of arranging an armored car to deliver credit card information from someone living in a cardboard box to someone living on a park bench." -- Gene Spafford Imagine sending Google an encrypted question and getting back the exact results you wanted — without them having any way of knowing what your question was or what result they returned. The technique to do that is called Fully Homomorphic Encryption (FHE). The first time I heard about what FHE does, I didn't believe it was possible. But it is — an it works in real-world systems today. It allows arbitrary computations on ciphertext (encrypted data) — without needing to decrypt it first. The result of the computation, once decrypted, matches the result as if it had been performed on plaintext (unencrypted data). From Craig Gentry's slides Moore's Law of FHE As FHE allows encrypted computation, users can keep their data encrypted all the time on the internet (sending, server computing, receiving back). This prevents any chance of data breach. Full Privacy. But then, why isn't it the default like HTTPS? Why isn't everyone using it? And why haven't most people even heard of? Because it is still not practical for most applications, as it is very slow. But this is changing fast as I'll explain below. Current FHE has 1,000x to 10,000x computational overhead compared to plaintext operations. On the storage side, ciphertexts can be 40 to 1,000 times larger than the original. It's like the internet in 1990—technically awesome, but limited in practice. Here's where it gets interesting: FHE algorithms are getting 8x faster each year. Operations that took 30 minutes per bit in 2011 now take milliseconds. See the graph below showing its dramatic speed improvement. ref The graph shows 10^12 times improvement until 2014. The pace of improvement continued over the la...