This book contains the proceedings of the 5th European Public Key Infrastr- ture Workshop: Theory and Practice, EuroPKI 2008, which was held on the NTNU campus Gloshaugen in Trondheim, Norway, in June 2008. The EuroPKI workshop series focuses on all research and practice aspects of public key infrastructures, services and applications, and welcomes original research papers and excellent survey contributions from academia, government, and industry. Simplyput, publickeysareeasiertodistributethansecretkeys.Nevertheless, constructing e?ective, practical, secure and low cost means for assuring auth- ticity and validity of public keys used in large-scale networked services remains both a technological and organizational challenge. In a nutshell, this is the PKI problem, and the papers presented herein propose new solutions and insight for these questions. This volume holds 16 refereedpapers including the presentationpaper by the invited speaker P. Landrock. In response to the EuroPKI 2008 call for papers, a total of 37 paper proposalswere received. All submissions underwenta thorough blind review by at least three PC members, resulting in a careful selection and revision of the accepted papers. The authors came from 10 countries: Belgium, Brazil, Canada, Finland, Germany, Japan, Malaysia, Norway, Spain, and the USA.Theacceptedpaperswereorganizedintothe topicalsessions: InvitedTalk, Certi?cates, Authentication, Practice, Signatures, Analysis, and Networks.