Indocrypt began in the year 2000 under the leadership of Bimal Roy and - docrypt 2005 was the sixth conference in this series. This series has been well accepted by the international research community as a forum for presenting high-quality cryptography research. This year a total of 148 papers were s- mitted for consideration to the Program Committee and after a careful review process, 31 were accepted for presentation. We would like to thank the authors of all submitted papers, including those that were accepted and those which, unfortunately, could not be accommodated. ThereviewingprocessforIndocryptwasverystringentandtheschedulewas- tremelytight.TheProgramCommitteemembersdidanexcellentjobinreviewing andselectingthepapersforpresentation.Duringthereviewprocess, theProgram Committee members were communicating using a review software developed by BartPreneel, WimMoreauandJorisClaessens.Weacknowledgethemforprov- ingthesoftware.ThesoftwarewashostedatI2R, Singaporeandwearegratefulto Feng BaoandJianyingZhouforallowingthat.Thisyear'sconferencewasdeeply indebtedto QiuYingofI2R, Singapore, who tookthe responsibilityofmainta- ing the review softwareand the server.Without his great cooperationIndocrypt 2005could nothavebeen possible.Inthis regardI wouldliketo acknowledgethe supportofTanmoyKantiDas, DibyenduChakrabarti, MridulNandi, Deepak- mar Dalai, Sumanta Sarkar and Sourav Mukhopadhyay for handling important administrativeissuesinthesubmissionandreviewprocessesaswellasforputting togethertheseproceedingsintheir?nalform.WearealsogratefultoPalashSarkar forhiscooperationandguidanceinIndocrypt2005. The proceedings include the revised versions of the 31 selected papers. Re- sions were not checked by the ProgramCommittee and the authors bear the full responsibility for the contents of the respective papers. Our thanks go to all the Program members and the external reviewers (a list of them is included in the proceedings) who put in their valuable time and e?ort in providing important feedbackto the authors.We thank V. KumarMurty ofthe UniversityofToronto for kindly agreeing to present the invited talk. The talk has been included in the proceedings.