Interview with Kyoohyung Han at EuroCrypt 2018 on the topic of Bootstrapping and Homomorphic Encryption

Kyoohyung Han is a PhD student in the Department of Mathematical Science at the Seoul National University in Korea. He recently gave a presentation at EuroCrypt 2018 titled Homomorphic Lower Digit Removal and Improved FHE Bootstrapping. He was generous enough to give me a few minutes of his time and talk a little more about his research and the importance of bootstrapping and homomorphic encryption.

Why is Bootstrapping important?

In broad terms, homomorphic encryption software typically provides a finite set of operations. With the aid of bootstrapping, we can transcend this constraint, thereby enabling us to perform an unlimited number of operations while the data remains encrypted.

What separates your method from previous methods?

With our method we have changed the middle step in bootstrapping. There is a process called Homomorphic Bit Extraction.

In our process, our method has lower depth and lower complexity. In our method, we use one more polynomial which is called Lowest Digit Removal Polynomial. In previous methods they used 3 kinds of function and our method uses 4 functions.

What is the advantage to your method?

It quicker and with smaller parameters

Are there any real life applications for your improved method?

In the cases of machine learning and data analysis in the encrypted states, you would need large depth computation of encrypted data. So we need to insert bootstrapping steps for every 5 or 6 situations so that the performance of bootstrapping goes well then this kind of application will go well.

If someone wants to use homomorphic encryption in the future, then bootstrapping will be necessary. Maybe if you are just using a simple application you wouldn't need any bootstrapping. But usually, when you have large depth computation the bootstrapping will be necessary.

Here is the complete presentation that Kyoohyung Han created for his talk on Lower Digit Removal and Improved FHE Bootstrapping at EuroCrypt 2018