7 - TPM Command Message Overview

Abstract

This chapter describes Trusted Platform Module (TPM) Command Message Blocks that help in understanding the various forms of TPM command input and output messaging. The TPM essentially has three levels of command authorization—namely, no authorization, single authorization, and two authorizations. The level of authorization depends on the number of TPM entities referenced within the command message being sent to the TPM. All TPM command input and output messages have a common header; and depending on the command, it can add information to the respective headers. In context to non-authorized TPM command category, these types of messages do not reference any particular type of TPM entity. The TPM determines the level of authorization by virtue of the message parameter defined as the authorization tag and by defining the possible values this type of parameter can hold. The generic header information contains the authorization tag, the parameter size, and the command code. All TPM input message blocks, regardless of authorization level, have this header information in common.