This book constitutes the refereed proceedings of the 13th Asian Computing Science Conference, ASIAN 2009, held in Seoul, Korea, in December 2009. The 7 revised full papers and 3 revised short papers presented together with 2 invited talks were carefully reviewed and selected from 45 submissions. Focusing on the theory and practice of information security and privacy, the papers include topics of deducibility constraints, symmetric encryption modes, dynamic security domains and policies, cryptography, formal verification of quantum programs, decision of static equivalence, authenticated message and proxy signature scheme.