The Phish-Market Protocol: Securely Sharing Attack Data between Competitors

Abstract

A key way in which banks mitigate the effects of phishing is to remove fraudulent websites or suspend abusive domain names. This ‘take-down’ is often subcontracted to specialist firms. Prior work has shown that these take-down companies refuse to share ‘feeds’ of phishing website URLs with each other, and consequently, many phishing websites are not removed because the firm with the take-down contract remains unaware of their existence. The take-down companies are reticent to exchange feeds, fearing that competitors with less comprehensive lists might ‘free-ride’ off their efforts by not investing resources to find new websites, as well as use the feeds to poach clients. In this paper, we propose the Phish-Market protocol, which enables companies with less comprehensive feeds to learn about websites impersonating their own clients that are held by other firms. The protocol is designed so that the contributing firm is compensated only for those websites affecting its competitor’s clients and only those previously unknown to the receiving firm. Crucially, the protocol does not reveal to the contributing firm which URLs are needed by the receiver, as this is viewed as sensitive information by take-down firms. Using complete lists of phishing URLs obtained from two large take-down companies, our elliptic-curve-based implementation added a negligible average 5 second delay to securely share URLs.