The Step Back That Helped Me Get A Ph.D. Position in Denmark

asphalt road between trees

My journey to Denmark

Spring 2009, Ho Chi Minh City, Vietnam. 

I completed the Master’s program in Mathematics.

A Vietnamese would then add the prefix “Thạc sĩ” (Master) whenever she introduced my name to others. 

With the Master’s degree, I officially became a staff (“biên chế”) at my institution. It was a public university in Vietnam. The government paid my salary, which was about 100 USD/month in 2009. 

That was not enough to survive in a huge city like Ho Chi Minh City. To increase your income, you have to work more and even outside your public institution.

Teaching was the major task of a lecturer. With a Master’s degree, you could get about 3 USD/hour teaching in 2009.

It was completely different if you got a Ph.D. Your teaching wage would be doubled. You could also earn different kinds of money from many other activities as a “Tiến sĩ” (Ph.D.) at a public organization in Vietnam. 

Supervisor. Committee. Head of a section. Head of a department. Etc.

You should have a Ph.D. degree. 

I should too.

But income and title were not the reasons that motivated me to continue the Ph.D. study. I needed it for my research, my teaching and for my students.

My Department of Mathematics and Computer Sciencehad opened new undergraduate modules. I was in charge of the courses of Arithmetics, Coding Theory, and Cryptography. 

You needed to strengthen the background on them, especially if you wanted to supervise students researching on these topics.

My Master’s thesis was about cryptography. It was a very young topic in Vietnam at that time, especially in Ho Chi Minh City. There was almost no expert on it.

The nearest experts that could be considered as cryptographers were two of my colleagues at the Department of Information Technology. Trần Minh Triết just finished his Ph.D. in crypto. Prof. Nguyễn Đình Thúc had just started his research group on this topic.

I decided to look for a Ph.D. study abroad.

Crypto positions were tough

I contacted one of my former colleagues Lê Triệu Phong, a cryptographer in Japan for some advice. My journey started. 

I applied to all well-known crypto groups. Japan. Singapore. Germany. England. France. Ireland. Luxembourg. All rejected. Such famous groups only accepted the best students in the world.

My background was not strong enough to get accepted for this very special research topic. 

Vietnam was still not on the map of cryptography. It was more difficult for a student who graduated from Ho Chi Minh City to apply for a Ph.D. position somewhere else in the world about this difficult topic.

Winter 2009. 

I met Nguyễn Phong Quang, one of the biggest names in Public-Key Cryptography. He was French but of Vietnamese origin. He visited his homeland for vacation and gave a short course on crypto at my university. 

I asked him for a Ph.D. position under his supervisor, but he refused. The senior researcher was having too many students at the moment. I lost one of the biggest opportunities. However, he helped me revise my resume.

Became a father

March 2011. 

Mai-Khanh said hello to the world with a big crying. For a young couple having kids, it was the biggest stage in their lives. 

Raising kids in Vietnam costs a lot of money. If you do not have much, you have to work more. We had, too. 

One day in April 2011 when drinking iced coffee during my breakfast, I got a phone call from one of my old students for a job offer. It was the company I used to refuse a job to go for the position at the university many years ago :). 

Now I could work more to earn more. Writing code on weekdays. Teaching courses on weekends.

July 2011. 

My wife was back to work after 4 months of parental leave. She managed the time to balance the work and her role as a mother. But as a bank worker, she might have some days coming home very late. 

In Vietnam, three generations are living the same home. My parents helped taking care of Mai-Khanh when we went to work. Leaving the working hours, we entered the parenting ones. The evenings were our turn.

We were exhausted.

Thuý sometimes said if I could earn 2.500 USD/month, she would be at home full-time taking care of our kid.

The step back

August 2011. 

Two years have gone by. I did not get a Ph.D. offer yet. 

I contacted again Phan Dương Hiệu, another cryptographer in France, for another piece of advice. He was a colleague of Nguyễn Phong Quang in L’École normale supérieure (ENS, Paris). 

After we discussed and analyzed my situation, he suggested me a step back to do another Master in Informatics to strengthen my CV.

What a brilliant idea!

Let me call him “anh Hiệu” (brother Hiệu) for short as I will mention him many times from now on.

The application to the Master program

The visa to study in France required the French language of level B2.

So I thought I needed some time to prepare for the language. But anh Hiệu encouraged me to start right away in 2011.

As he suggested, I applied for one of the most difficult Master’s programs in the world, Master Parisien de Recherche en Informatique (MPRI). He contacted a coordinator of the program and helped me refine my documents for the application.

Crypto requires both math and informatics. My Bachelor’s and Master’s degrees were only in math. So I needed such a Master’s program to strengthen my CV to apply for any math or computer science positions.

MPRI also had some specific courses on crypto. That was great.


The visa to study in France required also financial proof of at least 6.000 euros for one year. I did not have such a big money.

Anh Hiệu helped me find a solution for it. He suggested I should apply for a scholarship from Rencontres du Vietnam.

The foundation was founded by Prof. Trần Thanh Vân and Prof. Odon Vallet to support Vietnamese students studying in Vietnam and France. I got one for my Bachelor’s in Vietnam. Now I applied for another scholarship for a Master’s in France.

Prof. Trần Thanh Vân was one of the biggest names in the world of astrophysics. His strong network and his big love for Vietnam let him contribute a lot to the education and research in his homeland through different kinds of supports and establishments.

The foundation would give me a 6.000-euro cheque when I arrived in France. It was just enough for the visa requirement in one year. 

The language

Within only 1.5 months I conducted an intensive French language course in the evenings at Institut d’Echanges Culturels avec la France (IDECAF). 

During that time I was still working full-time as a maths lecturer and a software developer. This was a big mistake. Being not focused, my French language was not improved.

The French language of level B2 was still one of the visa requirements. I tried the multiple-choice test and passed it with huge luck.

First time in Paris

The arrival

Fall 2011, Paris, France. 

Nguyễn Tuấn Anh “nhí” picked me up from Charles de Gaulle airport.

He was one of my best friends in junior school. We prefixed him with “B” or “nhí” to distinguish him from the other two Nguyễn Tuấn Anh in our class. He came to France with his family many years ago. Now he was French and working as a software engineer.

The Peugeot stopped us at a small building for international students in District 19, where I would stay a few days with one of my former colleagues Nguyễn Hoàng Lộc before moving to another place.

Finding a place to stay in Paris was very difficult. I had contacted Dr. Lộc for help before flying to France. He and his wife accepted me some first stays after arrival when I was looking for a new place. Three of us had to stay together in the same room for a few weeks. A generous couple.

Dr. Lộc was working as a Postdoc at ENS. But he did not know anh Hiệu. I introduced them to each other.

Settle down 

Unable to speak French fluently, I found it very difficult to settle down for the first time in France. Actually, it was my first time out of Vietnam if you did not count a weekend tour to Cambodia.

I had a contact to help me from and, the communication channels of the association of Vietnamese students in France. The web-based forum was now replaced by a Facebook group for better communication and for free. 

Was a Master 1 student in informatics, Dương Hương Thủy helped me buy a sim card, showed me the way to school and introduced me to her network.

I also met Văn Bích Tuyền, a former colleague. She helped me buy the travel card to go around Paris. We tried also to apply for a healthcare card. But we quit due to its complexness.

I went to ENS to finally meet anh Hiệu in person for the first time after many online discussions. We went sushi for lunch. He drove me around Paris to introduce the city he was proud of being a Parisien. What a nice person he was.

What was the color of light in The City Of Light?

The Master study

MPRI was a research-oriented Master’s program in Computer Science. It was a joint program between the biggest universities in Paris. Most MPRI graduates would continue with a Ph.D.

The courses were very difficult. Moreover, most were in French. Very few were in English. I could not follow most courses because of the language or their complexity.

But I had the chance to study under very big names of the fields. 

My most favorite course was Arithmetic Algorithms for Cryptography. It was what I was teaching in Vietnam. It was the only course I was good at.

The courses became more and more difficult when they came to the final exam.

I failed Michel’s crypto course. A bad mark on Daniel’s coding. The only one I had a good mark on was Ben- and Emmanuel’s arithmetics.

I felt wrong to choose this difficult program. Very disappointed.

Keep looking for a Ph.D.

During my study, I still keep looking for Ph.D. positions around the world. Especially in France where I was now. There were many leading names here in Paris.

I asked Prof. Jean-Charles Faugère from Université Paris 6 (Sorbonne) for a Ph.D. on Gröbner basis. He was the biggest name in the area of solving polynomial equations. But my lack of la carte Vitale (healthcare card) prevented me from further processes. 

I still do not know why I could not get the card at that time. 

I also asked Prof. Phạm Xuân Huyên from Université Paris 7 (Diderot) for a Ph.D. in quantitative finance. He refused due to my different background.

The only researcher that I could ask for a Ph.D. in crypto was Nadia El Mrabet from Université Paris 8 (Vincennes-Saint-Denis). But we could not find the funding for the Ph.D.

I still kept an eye on the Open Positions in Cryptology of the International Association for Cryptologic Research.

One day I found an interesting Ph.D. position from Denmark about Coding Theory. I started a plan to attack it.

Ask for Recommendation

My best performance was on the course on Arithmetics. So I asked Emmanuel for a letter of recommendation (LOR). He refused. Then I asked Ben. He also refused but suggested I should ask his boss Daniel.

Prof. Daniel Augot was very kind. Though my result of his course on coding theory was not good, he agreed to write me a few lines for a LOR. He noticed I was the only student who could not speak French in his class.

The interview

Peter emailed me the proposed project and some publications to read. I refined the summary of my Master’s thesis in English and prepared all possible questions for the Skype interview.

The internet connection was too bad for a video call. At home, a poor student like me always hoped to catch free wifi somewhere nearby. 

Peter and Tom lost my sound after a few minutes. We decided to do the interview by phone. The interview went very easily. We talked about the project. About my Master’s study. About my situation. About the Ph.D. benefit.

They promised to give me the result in a few weeks.

Why I was accepted

My CV was unchanged for a long time. But as today I was in Paris, there were other things that helped me get accepted.

The biggest reason was Daniel and Tom were the leading names in the area of coding theory. They knew each other very well. If one recommended a student, the partner would accept him undoubtedly.

Another reason might be small but could be counted. There was a Vietnamese Ph.D. student at the section of Mathematics, where Peter and Tom were working. Because I came from Vietnam, Peter asked Nguyễn Đăng Mạnh if he knew something about me. We have never met before. But Mạnh said yes to his knowing me, just because he knew my supervisor’s name, Trần Nam Dũng. I got one vote from the countryman.

Trần Nam Dũng was famous in the Vietnam math community. The students could easily find his name in the series of “Math and Youth”, where he often contributed some interesting problems and articles. Mạnh was a big fan of the magazine.

March 2012, Paris.

I watched Mai-Khanh’s first birthday on Skype. It was one of the most important days of a child in Vietnam. But her father was in France now.

I cried a lot after the call.

End of that month, I decided to return to Vietnam.

July 2012, Ho Chi Minh City.

My wife decided to quit her good job at the bank. The young family started a new adventure in a small country very far away.

Thuý and Mai-Khanh (by Trịnh Ngọc Trung).


Getting a good Ph.D. scholarship is never easy. Especially for an average Vietnamese student like me. It is harder when you are applying for a difficult topic like crypto, which accepts only the best candidate.

There is always another way to get the goal

If I was still sitting in Vietnam and applied like before, my status might not be changed.

Sometimes you might need to go around to get the target. Though I did not complete the Master 2 in Paris, my presence there was the most important factor to my success.

You need help

If anh Hiệu did not help me to go to Paris, I could not meet Prof. Daniel. 

If Prof. Daniel did not help introduce me to Tom, I might not be accepted.

If Mạnh did not help contribute a vote, I might not be accepted. 

You have to actively ask for help

If I did not ask those angels for help, I could not share this story with you.

Good luck with your way!


Leave a Reply

Your email address will not be published. Required fields are marked *