This volume contains the papers presented at the International Workshop on Mathematical Methods, Models and Architectures for Computer Network Se- rity(MMM-ACNS2003)heldinSt.Petersburg, Russia, duringSeptember21 23, 2003.TheworkshopwasorganizedbytheSt.PetersburgInstituteforInformatics and Automation of the Russian Academy of Sciences (SPIIRAS) in cooperation with the Russian Foundation for Basic Research (RFBR), the US Air Force - search Laboratory/Information Directorate (AFRL/IF) and the Air Force O?ce of Scienti?c Research (AFOSR), the O?ce of Naval Research International Field O?ce (USA), and Binghamton University (SUNY, USA). The ?rst international workshop of this series, MMM-ACNS2001, May 21 23, 2001, St. Petersburg, Russia, hosted by the St. Petersburg Institute for - formatics and Automation, demonstrated the keen interest of the international researchcommunityinthetheoreticalaspectsofcomputernetworkandinfor- tion security and encouraged the establishment of an on-going series of brennial workshops. MMM-ACNS2003 provided an international forum for sharing original - search results and application experiences among specialists in fundamental and applied problems of computer network security. An important distinction of the workshop was its focus on mathematical aspects of information and computer networksecurityandtheroleofmathematicalissuesincontemporaryandfuture development of models of secure computing."