Vicente Benjumea Javier Lopez José A. Montenegro José M. Troya A First Approach to Provide Anonymity in Attribute Certificates. 402-415 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2947&spage=402 2004 conf/pkc/2004 Public Key Cryptography db/conf/pkc/pkc2004.html#BenjumeaLMT04