CITS – Workshop on Factoring Large Integers

Workshop on Factoring Large Integers

BSI-LogoOn September 11./12. there will be a workshop on Factoring at the Ruhr-University Bochum. It is organized by the Federal Office for Information Security (BSI) and the Chair of Cryptology and IT-Security.
Everyone interested in the topic is welcome.
The workshop will take place in Veranstaltungsraum 2 (room number 01/53), which is located at level 01 in the mensa building.

Invited Speakers

  • Daniel J. Bernstein, University of Illinois at Chicago
  • Willi Geiselmann, Karlsruhe University
  • Antoine Joux, Université de Versailles
  • Tanja Lange, Technische Universiteit Eindhoven
  • Claus-Peter Schnorr, Goethe-University Frankfurt
  • Francesco Sica


Friday, 11th
9:30-10:15Antoine Joux, DGA and Université de Versailles
Factoring pq² with hints (Abstract Slides)

In this talk, we show how a homogeneous version of Coppersmith’s small root algorithm can be applied to the problem of factoring numbers of the form N=p^2q, when given some additional side information. This can be applied to break a variant of the NICE cryptosystem called REAL-Nice.

10:15-11:00Colin Stahlke, Edizone and Ruhr-University Bochum
Some Remarks on Polynomial Selection in the GNFS (Abstract Slides)

The last step of the polynomial selection process in the GNFS is the local optimization. For a 768 bit number we speed up this part from several CPU years to 400 CPU hours. In the second part, we check that partial sieving gives a hint about the quality of a polynomial pair. Then we improve one of Murphy’s quality functions using the data of several thousand polynomial pairs.

11:30-12:15Claus-Peter Schnorr, Goethe-University Frankfurt
Average-Time Fast SVP and CVP Algorithms:
Factoring Integers in Polynomial Time (Abstract Slides)
14:00-14:45Willi Geiselmann, University Karlsruhe
Sieving Hardware for the NFS: Architectures and their Bottlenecks (Abstract Slides)
14:45-15:30Ralf Zimmermann, Ruhr-University Bochum
Implementing the Elliptic Curve Method (ECM) on Special-Purpose Hardware (Abstract Slides)
16:00-16:45Daniel Loebenberger, B-IT Bonn
Optimization strategies for hardware-based cofactorization (Abstract Slides)
16:45-17:30Francesco Sica
Striding Towards a New Subexponential Factoring Algorithm (Abstract Slides)
Saturday, 12th
9:00-09:45Tanja Lange, Technische Universiteit Eindhoven
ECM using Edwards curves (Abstract Slides)
09:45-10:30Mathias Herrmann, Ruhr-University Bochum
Polynomial Selection Using Lattice Reduction (Abstract Slides)
11:00-11:45Stefan Baumgart, Kiel University
COPACOBANA and Upcoming Architectures for Cryptanalysis (Abstract Slides)
11:45-12:30Daniel J. Bernstein, University of Illinois at Chicago
ECM speed records on CPU and GPU (Abstract Slides)


The workshop is free of charge, but for organisatorial reasons, we kindly ask everyone who plans on attending the workshop to register until 8 Sep.

Registration closed!


  • We recommend the ParkInn Hotel (90 Euro per night)
    To get the Corporate Account ID of Ruhr Univerity Bochum, please send a short note to mathias.herrmann’at’ or marion.reinhardt’at’
  • A cheaper alternative is the Ibis Zentrum (approx. 60 Euro per night)

How to get there

Getting to Ruhr-University from Bochum Central Station
The workshop will take place in the VeranstaltungszentrumLageplan1-VZ.pdf