"That’s when my heart started racing"
Kristina Hostáková joined Professor Dennis Hofheinz’s research group at the Institute of Theoretical Computer Science last December as a postdoc. In this interview, she talks about asymmetric cryptography, her experiences on the path to ETH Zurich and the promotion of women in computer science.
Kristina, last December you joined the research group led by Professor Dennis Hofheinz. How have you been these past three months?
Fine, although I’m living out of boxes at the moment! My partner and I just moved to a permanent flat in a green neighbourhood in Zurich. As a computer scientist, working from home is not a problem for me. But I’m really glad that I managed to meet most of my new colleagues in person last year. These days, we have regular Zoom meetings, where we talk about research and also our personal lives. I feel well integrated.
How did your journey from a maths-savvy high school girl in the Czech Republic to a cryptography postdoc at ETH unfold?
I took my first programming courses in high school, where I had chosen a math-intensive track. However, my interests ranged from maths to languages and even sports psychology. At first, I didn’t know what I wanted to study. That changed when I went to a study information day at the Mathematics Department of the Charles University in Prague. During a presentation on cryptography, I just knew that was the subject I wanted to dive into. After studying maths with a strong cryptography focus in Prague, I went on to Ruhr University Bochum in Germany where I started my Ph.D. in Applied Cryptography. When my supervisor moved to the Technical University of Darmstadt, I also moved there and completed my Ph.D. in Darmstadt last year. It was during my doctoral studies that I learned about Dennis Hofheinz and his research from a colleague, Julia, who had completed her Ph.D. with him as her supervisor. I contacted him when I was looking for a postdoc position. Last summer, we met in person and discovered that our research interests are aligned and that we also got along well on a personal level.
While talking about that first presentation on cryptography, your face lit up. What triggered your fascination?
When I learned about external pagepublic-key cryptography, also called asymmetric cryptography, my heart started racing and I just had to know how it works. Before the discovery of the asymmetric key cryptosystem in the 1970s, two people exchanging secret messages always had to agree on a decryption key. A simple historical example of such an encryption technique is the external pageCaesar cipher. In asymmetric cryptography, two different keys are used. One key is public – it’s published on the internet, for example – and the other key is secret. Using the public key, anybody can encrypt a message. However, the only person in the world who can decrypt the message is the holder of the second, secret key. That fascinating principle is also essential to my current research on digital signatures.
What is a digital signature and why is it useful?
A digital signature has a similar purpose to an analogue signature. It confirms that an entity with a certain identity – a person, a group of people or a company – has authorised a given message, for example, a contract. An additional property of a digital signature that has increasing importance is quantum-resistance. With that property, a signature will also be secure once quantum computing is possible. The main purpose of digital signatures is to make sure people can communicate and interact safely within the digital space. This is highly important in our globalised world, and even more so during the current pandemic.
"As a cryptographer, you always have to find the right balance between security, financial factors, and efficiency." Kristina Hostáková
Can you give an example of a specific research project?
I’ve been working on digital two-party signatures. Imagine you and your friend want to rent a flat together and you both have to sign a digital contract. To do so, you can either both sign individually, or you can create one joint signature by smartly merging the two individual signatures. The benefit of the joint signature is that it takes less storage space and is thus more cost-effective. In large applications, where each piece of information is duplicated and stored in many places, needing less storage can make a big difference in terms of costs. As a cryptographer, you always have to find the right balance between security, financial factors and efficiency. If a digital process, for example an online payment, is maximally secure but takes 30 minutes to complete, it is not user-friendly and will only remain a nice theory.
You are part of our Women in Computer Science network. What is your role in CSNOW?
I share the leadership of the group with Joel Wanner and Mridula Singh, both of whom are doctoral students. What I find remarkable about CSNOW is its diversity. The network includes students of all levels, postdocs and even professors. Also, we have men in our group. That’s essential. The lack of women in computer science is an issue that affects the entire computer science community – and should therefore be tackled collectively.
In your opinion, what are the main factors causing the low percentage of women in computer science?
I think it’s a complex problem with no simple solution. I feel that role models are very important. As a student, you are still figuring out your future path. And in that process, everybody – regardless of their gender – experiences some insecurity. However, having role models to look up to can have a highly encouraging effect at that stage. And that’s where female students are at a disadvantage. They look around and mostly see male professors. That doesn’t fuel confidence but raises questions. This is why it’s great that our department hired five new female faculty members last year. Further, I think high school girls often don’t realise how broad the field of computer science is. In my opinion, kids in general, and girls especially, should get an insight into programming as early as possible, so they can get a feel for the creativity and interdisciplinarity that goes along with computer science
"I think high school girls often don’t realise how broad the field of computer science is." Kristina Hostáková
Why are there still so few female role models despite active efforts on the part of universities and other organisations?
We are dealing with a two-fold problem. First, the talent pool of female computer science students is small to begin with. Second, the percentage of women going into research is relatively small in all sciences, which is probably a result of various factors, including the previously mentioned lack of role models. I can only talk from my own experience as a researcher. Within the past few years, I moved home three times. That took a lot of energy and detached me from friends and family. Following your passion for research comes at a high price to pay for anybody, regardless of gender.
What have you learnt along your path?
First, to be proactive. If you are missing something, create it yourself; don’t let the curriculum or existing course offerings stop you. When my peers and I thought it would be great to have a seminar to discuss current developments in cryptography, we just started one ourselves. The faculty liked the idea and offered such a seminar themselves the following semester. Second, to follow your passion. If a particular subject lights your fire, take it seriously and find a way to make your dream come true. You can always change it later if it doesn’t work out. I’m also still figuring out whether the academic path is for me. So far, I’m very much enjoying what I do. I know that there are some challenging steps ahead, but I’ll see how I deal with them when I get there (laughs).
