A trusted input technique in which switching is made between an OS environment unreliable in security and a BIOS reliable in security. Rapid switching to a secure environment, such as BIOS mode, upon request for secure input, is enabled. An OS environment of a user can be quickly resumed after the user completes the input of a cryptogram. The technique does not and will not have any influence on secure transaction architecture. The identification of a server is authenticated in a trusted secure environment, and thus it is possible to prevent such problem as “phishing” websites. The user cryptogram is present as plaintext only in a BIOS environment and server and as encrypted during intermediate transmission. Thus, it is impossible to be intercepted by any virus such as a “Trojan horse”.