------------------------------------------------------------------------------- Mohamed Gouda CS 386 S Spring 2008 Quiz#1 ------------------------------------------------------------------------------- Show that if the three grid protocol is reduced to a two-grid protocol by getting rid of AC, the resulting protocol is incorrect. Hint : Consider the case when n = 8. Consider AB-grid and BC-grid. Give 3 processes p(u,v,w), p(u',v',w') and p(u'',v'',w'') and show that the computed set SK by p(u,v,w) and p(u',v',w') is also assigned to p(u'',v'',w''). ------------------------------------------------------------------------------ (Solution) Suppose we restrict ourselves to the 2 grids AB and BC. Suppose p(u,v,w) and p(u',v',w') want to communicate securely where u != u' and w != w'. Their set of common keys are a) AB-g(*,v) b) BC-g(v,*) c) AB-d(u,v)(u',v) d) BC-d(v,w)(v,w') However, all these keys are known to process p(u,v,w').