The advance of IT and the Internet makes it easy to transmit andshare data with friends and colleagues using intermediatesystems, such as USB flash drive, email, and file hosting service.Because they involve security risks, people often secure datawith access control mechanisms to counteract threats. There aretwo approaches: file-based and server-based. In the former case,a file is encrypted or password-protected. It requires a secure wayto deliver secret information, including encryption key orpassword, to the parties. In the latter case, users are highlydependent upon the service and administration, and can trust itcompletely. Public-key cryptography solves these problems. It isan asymmetric cryptography system assuring the confidentiality,authenticity, and non-repudiability. However, it is limited to oneto-one encryption between two users and unsuitable for sharingthe same secret information among multiple people.
展开▼
