Collusion attack on a multi-key secure video proxy scheme

In ACM Multimedia'2002, a video proxy scheme was proposed for secure video delivery. In the scheme, a video is cached in proxies in encrypted form so that it remains non-disclosed even if the proxies are compromised. The proxies re-encrypt the video before its distribution, and different clients would receive different keys for the protected video. In this paper we present a security analysis on the scheme and show that the scheme is subject to collusion attack. Two or more clients working together can find out video server's secret keys and hence compromise the system. The countermeasure to the collusion attack is presented.