Rolf Oppliger 
Secure Messaging on the Internet [PDF ebook] 

This book offers a comprehensive understanding of secure Internet messaging, and brings together all the relevant and critical information needed to use Open PGP and S/MIME-compliant software. It explores the conceptual and technical approaches followed by the developers of both Open PGP and S/MIME, and gives a thorough treatment of the latest and most-effective technologies for secure messaging.Ideal for security and network managers, as well as professional system and network administrators, this easy-to-understand book is a complete guide to Open PGP, S/MIME, Web-based and gateway solutions, certified mail, delivery platforms, and instant messaging.