On the Cryptographic Utilities of Social Networkswith case study on exploiting social networks for threshold cryptography

Shouhuai Xu and UTSA TeamUniversity of Texas at San Antonio (http://www.cs.utsa.edu/~shxu)

Motivation

Design considerations and preliminary results

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.

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)?

S: #

of c

ompr

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ed p

rivat

e ke

ys

T: # compromised users

S = T

: no

thre

shold

cryp

to (b

ench

mar

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best attack-resilience but worst availability (corresponding to complete graph, namely each user shares it key to all the other users)

bad

atta

ck-

resil

ience

good

atta

ck-re

silien

ce

worst attack-resilience but best availability (each user gives a copy of its private key to all other users)

better attack-resilience

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.