University of Twente Student Theses


Practical Client Puzzle from Repeated Squaring

Jeckmans, A.J.P. (2009) Practical Client Puzzle from Repeated Squaring.

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Abstract:Cryptographic puzzles have been proposed by Merkle [15] to relay secret information between parties over an insecure channel. Client puzzles, a type of cryptographic puzzle, have been proposed by Juels and Brainard [8] to defend a server against denial of service attacks. However there is no general framework for client puzzle schemes. In this thesis we present a general client puzzle framework. Since their introduction various types of client puzzles have been devel- oped. One such client puzzle is based on the time-lock secret release scheme created by Rivest et al. [17]. The time-lock secret release scheme uses re- peated squaring to hide information. Repeated squaring oers a determinis- tic puzzle that is not parallelizable by multiple computers. The drawback of the repeated squaring puzzle scheme is that it is computationally expensive and requires the server to keep state information. In order to develop a generally practical client puzzle scheme the re- peated squaring puzzle scheme has been modied. The computational com- plexity is improved by introducing batch verication. The scheme is also made stateless by altering the way puzzles are created. Analyses show that the result is a client puzzle scheme with more advantages.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:54 computer science
Programme:Embedded Systems MSc (60331)
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