Min-Shiang Hwang Cheng-Chi Lee Shin-Jia Hwang Cryptanalysis of the Hwang-Shi Proxy Signature Scheme. 131-134 2002 53 Fundam. Inform. 2 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=53&issue=2&spage=131 db/journals/fuin/fuin53.html#HwangLH02