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),...