Search-carrying code

Abstract

In this paper, we introduce a model-checking-based certification technique called search-carrying code (SCC). SCC is an adaptation of the principles of proof-carrying code, in which program certification is reduced to checking a provided safety proof. In SCC, program certification is an efficient re-examination of a program's state space. A code producer, who offers a program for use, provides a search script that encodes a search of the program's state space. A code consumer, who wants to certify that the program fits her needs, uses the search script to direct how a model checker searches the program's state space. Basic SCC achieves slight reductions in certification time, but it can be optimized in two important ways. (1) When a program comes from a trusted source, SCC certification can forgo authenticating the provided search script and instead optimize for speed of certification. (2) The search script can be partitioned into multiple partial certification tasks of roughly equal size, which can be performed in parallel. Using parallel model checking, we reduce the certification times by a factor of up to n, for n processors. When certifying a program from a trusted source, we reduce the certification times by a factor of up to 5n, for n processors.