Homomorphic encryption

I've run into a few people working on this over the last five years or so, but they've been a bit cagey about discussing their use cases and customers.

Any public applications outside of blockchain?

Online voting.

That's the big one.

There are as many usecases as there is sensitive data! Some of the obvious ones are automated medical diagnosis, genomics, biometric authentication, fraud detection, etc. What has prevented those usecases from happening at scale is the performance of homomorphic schemes

How does computation on encrypted data relate to voting systems?

To address the inevitable “what is this useful for” questions, my go-to example is cryptographic voting mechanisms.

The idea is that you segment a large integer into a couple of different bins by its bitwise representation. So you have a 60-bit integer and you segment it into four 15-bit bins. You use one of those to randomize what the encrypted versions are going to be, and you use the other three for different vote tallies of three candidates for some office.

You can then hand people three numbers each corresponding to a different candidate, and ask them to commit to one as their vote. Public authorities can then aggregate votes which they cannot actually see, and we don't decrypt until we get to some large enough context where your vote has been anonymized among ten thousand others, and you can check that the random seeds have been properly added, or other such things.

This also allows you to create a big online database where anybody can see their vote was counted, but nobody can figure out who someone else voted for.

There is a slight difficulty in that you cannot see directly what your numbers are actually voting for, so that the machines you are using to vote with need to be able to decrypt a ballot for you and then immediately destroy it, to verify that it was what you thought it was, so that you can trust that your three numbers do not all happen to vote for the same person because if someone tried that on any scale that could affect an election, even if they only poison 1% of ballots in a 500 person district, if everyone burns one to test the system then the fraud gets discovered at least once with 99.3% certainty. But the point is that all of these other issues can be handled “out-of-band” once you protect the important stuff.