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Esecurity: secure internet & e-cash

Corresponding entry in Aachen Campus, Bonn Basis Media Informatics, Bonn Basis CS-Master.


Prof. Dr. Joachim von zur Gathen


Michael Nüsken


Raoul Blankertz

Time & Place

First meeting: Tuesday, 03 April 2012 at 1330, b-it bitmax.

All times subject to agreement in class.


Exam: 27 July 2012, 1000-1300, b-it seminar room 2.1.

Post-exam meeting: 31 July 2012, 1400, b-it cosec seminar room 1.25.


The screen notes (PDF 23.3MB) contain all handwritten stuff (last updated 11 July 2012, 17:22).



4+2 SWS, 8 credits. Optionally, 3+2 SWS, 6 credits.

Successful completion of the course yields 8 credit points. For students who only want 6 credit points, a breakpoint at about 3/4 of the teaching time will be defined, and only the course material up to that point will be relevant for their exams and grades.


Basic knowledge in cryptography is needed, as for example the course Cryptography held in the previous winter. Compare our programme.


This course is about various aspects of security in the internet. In the first part we deal with secure connections, whereas the second part considers electronic voting schemes involving further tasks.

In the internet a large variety of protocols ("chatting programs") are in use to make this or that `secure'. VPN, IPsec, SSL, PKI, PGP are just a few tokens that need explanations. We will try to understand a little of that and how things are used and made available.

The application issue this year deals with electronic cash. There are a variety of proposals about how to realize a counter part to real coins (cash!) in the internet. However, most of the approaches that are used in practive are account based. But then transactions are not anonymous. What we are heading for in this chapter are systems that are as anonymous as real coins are. In particular, they must be account free since otherwise the account manager sees all transactions. Thus a certain bit string may be a valid coin. The problem with bit strings as compared to real coins is: they are fairly easy to copy. But one should not be able to just duplicate coins because that would render that kind of coin worthless. There are solutions to this double spending problem. Further issues then arise: real coins can be transferred many times from owner to owner, in case of extortion we may want a tracing option, ...



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