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Daniel A. Nagy

My picture High Tatras, Slovakia, July 2002

About Myself

I'm a telecommunications engineer with a strong interest in mathematics and its various applications. I was born in 1977, in Leningrad, USSR on the eve of St. Patrick's day. Since then, I have lived, worked and studied in several countries, while the world has changed beyond recognition many times over with no end in sight. Fortunately, 2×2=4 everywhere all the time.

My CV is available here in plain text together with its digital signature.

Contact Information

In Europe

Mailing address:
Nagy Dániel
Rákospatak park 2, 15.
Budapest, H-1142
+36 30 215-8843

In Cyberspace

E-mail: (ePoint System) (Alma Mater)
PGP public key fingerprint:
84C6 4245 F039 5B32 71E5 B8A0 A47C 89CB C167 EFEF

Current Projects

Online Payment: the ePoint System

Despite the recent advances in information technology and electronic commerce, online payment is still a mess. The Internet is infested with advertising, because very often that is the only way to finance a website or a community service. Individuals and businesses involved in digital commerce regularly suffer heavy losses to credit card fraud and identity theft, which pose an ever-increasing risk on the Internet. Yet, when we do business online, we are often forced to disclose an incredible amount of very personal information to our business partners — complete strangers in many cases.

The primary reason for the above situation is that there is no cheap, secure, yet anonymous method of on-line payment. Many attempts at introducing the digital equivalent of cash failed. And not for the lack of trying!

The challenges are enormous, as the Internet is radically different from our usual marketplaces: there is no single jurisdiction, no physical presence, and no easy way to demonstrate the ability to follow up on promises. And perhaps most importantly, there are no laws of conservation; pieces of information can be multiplied without restrictions at practically zero cost. One who gives information away is still in possession of it after the act.

Hence, I believe that a successful digital medium of exchange should be in many ways radically differnet from money, while at the same time retaining some of its properties. Correctly identifiing these properties is not easy and the pitfalls are numerous. The ePoint System is an ambitious project aimed at overcoming these difficulties and providing the Internet with a usable medium of exchange and credit.

Free and Open Source Software

Without the freedom and the abundance provided by Free and Open Source software (FOSS), life would be much harder and definitely less fun. As someone who regularly benefits from the work of the countless people contributing to the body of FOSS, I feel the moral obligation to share with the community the software that I write and consider useful for others, under the same fair terms.

A lightweight OpenPGP implementation in Java. This library is used for the client-side applications in the ePoint project, but there is nothing project-specific in there. It is aimed at applets and embedded applications. Not recommended for server-side use.
Contract facilitates the handling of documents that are processible by both humans and machines. Contracts in e-commerce are one possible application, but the programs in this package are not limited to any particular use.
Apache web server module for serving web content in exhange for OpenPGP-signed micropayment confirmations.
A lightweight AVL tree implementation in ANSI C. Intended for embedded use but by no means restricted to it. The library does not handle memory allocation; it is left to the developer.
Binary Suffix Tree library in ANSI C. This library has been used for my PhD research, but it is yet to be published. It is work in progress. Please be patient.

Literary Projects

I write a lot. It helps me in organizing my thoughts and feelings, in coming to terms with myself and the world around me. However, most of my pennings are not meant to be published or are not up to my own (admittedly not too high) literary standards.

Here are some writings of mine that I am comfortable sharing with the public. They are all work in progress, thus suggestions and criticism are most welcome.

Russian Tea HOWTO (in English)
This is a parody to Linux Documentation Project HowTo's, first published on April 1st, 2001. For a brief period of time, it was actually part of TLDP. Have a nice cup of tea!
Nasreddin Hodja in our world (blog in English)
This blog mostly consists of paraphrased Central-Asian folklore stories, but quotes from sages and other things of interest may end up there as well.


Discrete Mathematics

A first-year undergraduate course at Budapest University of Technology and Economics instructed by professor András Recski, comprising selected topics from algebra, combinatorics, complexity theory and number theory. As far as I know, its name has been changed to something like Introduction to Computer Science or Elements of Computer Science depending on the target audience.

I was leading tutorial sessions, grading midterm and final exams and preparing problems for these. And proctoring, of course.

Numerical Methods

A second-year undergraduate course at Queen's University instructed by professor Leslie Roberts. Calculations and error estimation with floating-point numbers, interpolation, numerical solutions of systems of linear equations and differential equations. Number-crunching, in short.

My duties included leading tutorial sessions and laboratory excercises.

Multivariable Calculus

A second-year undergraduate course at Queen's University instructed by professor Mike Roth. Quoting his definition: A course in calculus. Now with extra variables!. While teaching it, I was convinced that the official title was Vector Calculus.

I have led some tutorials, graded some homework assignments and invented problems for these. I have also contributed some material on the Wave Equation, drawing on the experience of the previous course.

Stochastic Processes

Combined fourth-year undergraduate and graduate course at Queen's University instructed by Ana Maria Savu. Probabilistic modeling, Markov-chains, queueing theory, etc. A very challenging course on both sides of the pulpit.

My duties included tutorials and homework grading.

Source Coding and Quantization

Co-instructed this combined fourth-year undergraduate and graduate course at Queen's University with professor Tamás Linder. Theoretical and practical aspects of lossy and lossless data compression: Scalar and vector quantization, entropy coding, algorithms — design and analysis.

I was giving the lectures.

Applied Cryptography

Elective course at Eötvös Lóránd University. Basic concepts of security engineering and applications of various cryptographic techniques, with an emphasis on physical security.

I am the instructor of this course.

Publications Available Online

Digital Payment

PhD Studies

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