We analyze the notion of "local names" in SPKI/SDSI. By interpreting local names as distributed groups, we develop a simple logic program for SPKI/SDSI's linked localname scheme and prove that it is equivalent to the nameresolution procedure in SDSI 1.1 and the 4-tuple-reduction mechanism in SPKI/SDSI 2.0. This logic program is itself a logic for understanding SDSI's linked local-name scheme and has several advantages over previous logics, e.g., those of Abadi [1] and Halpern and van der Meyden

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... [13] . We then enhance our logic program to handle authorization certificates, threshold subjects, and certificate discovery. This enhanced program serves both as a logical characterization and an implementation of SPKI/SDSI 2.0's certificate reduction and discovery. We discuss the way SPKI/SDSI uses threshold subjects and names for the purpose of authorization and show that, when used in a certain restricted way, local names can be interpreted as distributed roles.