Shouhuai Xu and UTSA Team University of Texas at San Antonio (cs.utsa/~shxu)

1. Motivation • Context: Our project “security for, and by social computing/networks” • Here we discuss the “by” part, with emphasis on cryptographic utilities of social networks and case study on exploiting social networks for threshold crypto. On the Cryptographic Utilities of Social Networkswith case study on exploiting social networks for threshold cryptography Design considerations and preliminary results Given social network G=(V, E). How should one shares her private key to her friends? • We consider the contradicting attack-resilience and availability (due to P2P nature of social networks) and consider the networked system as a whole. • What is optimal attack (NP-hard!) & optimal trade-off between them under the attack? • Psychological soundness: one holds a decisive share of her key so that even if all of her friends are compromised (or turn against her), her key is still secure. • What is the impact of various parameters, including social network structure? • What is the security utility of anonymous social networks (which can downgrade attack power from adaptive attacks to random attacks)? worst attack-resilience but best availability (each user gives a copy of its private key to all other users) best attack-resilience but worst availability (corresponding to complete graph, namely each user shares it key to all the other users) bad attack-resilience Shouhuai Xu and UTSA Team University of Texas at San Antonio (http://www.cs.utsa.edu/~shxu) S = T: no threshold crypto (benchmark) S: # of compromised private keys good attack-resilience better attack-resilience T: # compromised users Design space Heuristically optimal attack: choosing nodes from remainder graphs with decreasing degree Security utility of anonymous social networks Security utility of psychological soundness Note: see slides for details; extended abstract appeared in ACM AsiaCCS’08; full version in submission.