J. Alex Halderman, Brent Waters. Harvesting verifiable challenges from oblivious online sources. In Peng Ning, Sabrina De Capitani di Vimercati, Paul F. Syverson, editors, Proceedings of the 2007 ACM Conference on Computer and Communications Security, CCS 2007, Alexandria, Virginia, USA, October 28-31, 2007. pages 330-341, ACM, 2007. [doi]
Abstract is missing.