Lawrence O'Gorman Amit Bagga Jon Louis Bentley Call Center Customer Verification by Query-Directed Passwords. 54-67 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3110&spage=54 2004 conf/fc/2004 Financial Cryptography db/conf/fc/fc2004.html#OGormanBB04