Yevgeniy Dodis Pil Joong Lee Dae Hyun Yum Optimistic Fair Exchange in a Multi-user Setting. 118-133 2007 conf/pkc/2007 Public Key Cryptography http://dx.doi.org/10.1007/978-3-540-71677-8_9 db/conf/pkc/pkc2007.html#DodisLY07