This book constitutes the thoroughly refereed post-workshop proceedings of the 25th International Workshop on Security Protocols, held in Cambridge, UK, in March 2017. The volume consists of 16 thoroughly revised invited papers presented together with the respective transcripts of discussions.  The theme of this year's workshop was multi-objective security and the topics covered included security and privacy, formal methods and theory of security, systems security, network security, software and application security, human and societal aspects of security and privacy, security protocols, web protocol security, and mobile and wireless security.