The4th Workshopon Information Security Applications(WISA2003)wassp- sored by the following Korean organizations and government bodies: the Korea Institute of Information Security and Cryptology (KIISC), the Electronics and Telecommunications Research Institute(ETRI), andthe Ministryof Information and Communication (MIC). The workshop was held in Jeju Island, Korea – ring August 25-27, 2003. This international workshop provided ample technical sessions covering a large spectrum of information security applications. Subjects covered included network/mobile security, electronic commerce security, digital rights management, intrusion detection, secure systems and applications, bio- trics and human interfaces, public key cryptography, and applied cryptography. The program committee received 200 papers from 23 countries (representing most geographic areas where security and applied cryptography research is c- ductedthroughouttheworld).Eachsubmittedpaperwaspeer-reviewedbythree program committee members. This year, we had two tracks: long and short p- sentation tracks. We selected 36 papers for the long presentation track and 34 papers for the short presentation tracks. This volume contains revised versions of papers accepted for the long presentation track. We would like to note that getting accepted to both tracks was an achievement to be proud of, given the competitive nature of WISA this year. Papers in the short presentation track were only published in the WISA preproceedings as preliminary notes; ext- dedversionsofthesenotesmaybepublishedbyfutureconferencesorworkshops.