Selected publications by Stefan Schwoon

We introduce SDSIrep, a reputation system based on the SPKI/SDSI authorization system. It is well-known that a system of SPKI/SDSI certificates corresponds to the formal model of a pushdown system (PDS). Our system, SDSIrep, allows principals to express trust and recommendations in the form of so-called certificates with weights. By interpreting weights as probabilities, we obtain a random-walk model of the reputation of a principal. Thus, SDSIrep represents an application of the theory of probabilistic PDSs to the field of computer security. We present an algorithm to compute the reputation of each principal. An extension of SDSIrep also provides for so-called intersection certificates, by which, loosely speaking, a principal gains reputation if recommended by all members of a given group of principals. On a formal-methods level, this extension makes SDSIrep correspond to probabilistic alternating PDSs, and we extend the underlying theory of PDSs to handle this case. As an example we sketch a small academic reputation system that combines information from different reputation sources, like conferences, coauthors, and rankings.

   address = {Budapest, Hungary},
   author = {Bouajjani, Ahmed and Esparza, Javier and Schwoon, Stefan and Suwimonteerabuth, Dejvuth},
   booktitle = {{P}roceedings of the 14th {I}nternational {C}onference on {T}ools and {A}lgorithms for {C}onstruction and {A}nalysis of {S}ystems ({TACAS}'08)},
   DOI = {10.1007/978-3-540-78800-3_39},
   editor = {Ramakrishnan, C. R. and Rehof, Jakob},
   month = mar # {-} # apr,
   pages = {501-516},
   publisher = {Springer},
   series = {Lecture Notes in Computer Science},
   title = {{SDSI}rep: A~Reputation System based on~{SDSI}},
   url = {},
   volume = {4963},
   year = {2008},

About LSV