It's not what you know, but who you know: a social approach to last-resort authentication.

Stuart E. Schechter Serge Egelman Robert W. Reeder It's not what you know, but who you know: a social approach to last-resort authentication. 1983-1992 2009 CHI http://doi.acm.org/10.1145/1518701.1519003 conf/chi/2009 db/conf/chi/chi2009.html#SchechterER09