This paper proposes user authentication methods and encryption techniques that support reliable u-City user authentication services, based on biometric technology, (the use of face, vein, fingerprint, and iris recognition). Even in an advanced wire/wireless network environment, there remain the possibilities that personal confidential information may be exposed. Therefore, this paper proposes a method that prevents damage and effectively copes with security vulnerabilities, using an encryption method that applies to characteristics information twice, in addition to an authentication method based on biometric technology. The proposed user authentication technique randomly selects several biometric information items at the time of authentication, and applies more than two items of biometric information. In addition, the proposed encryption technique uses double encryption, utilizing the user's biometric characteristics information. This paper aims to guarantee an efficient and reliable user authentication service in a u-City environment, based on this methodology.