ACNS2009, the7thInternationalConferenceonAppliedCryptographyandN- work Security, was held in Paris-Rocquencourt, France, June 2-5, 2009. ACNS 2009 was organized by the Ecole Normale Sup erieure (ENS), the French - tional Center for Scienti?c Research (CNRS), and the French National Institute for Researchin Computer Science andControl(INRIA), in cooperationwith the InternationalAssociation for CryptologicResearch(IACR). The General Chairs of the conference were Pierre-Alain Fouque and Damien Vergnaud. Theconferencereceived150submissionsandeachsubmissionwasassignedto at least three committee members. Submissions co-authored by members of the Program Committee were assigned to at least four committee members. Due to thelargenumber ofhigh-qualitysubmissions, thereviewprocesswaschallenging andwearedeeplygratefulto the committeemembersandthe externalreviewers for their outstanding work. After meticulous deliberation, the Program C- mittee, which was chaired by Michel Abdalla and David Pointcheval, selected 32 submissions for presentation in the academic track and these are the articles that are included in this volume. Additionally, a few other submissions were selected for presentation in the non-archival industrial track. The best student paper was awarded to Ayman Jarrous for his paper "Secure Hamming Distance Based Computation and Its Applications," co-authoredwith Benny Pinkas. The review process was run using the iChair software, written by Thomas Baigneres and Matthieu Finiasz from EPFL, LASEC, Switzerland and we are indebted to them for letting us use their software. The programalso included four invited talks in addition to the academicand industrial tracks."