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History of TPM 2.0 Specification Development

The specification made slow but steady progress for several years, with features being debated, added, and deleted. David Grawrock of Intel was the chair of the specification committee; under his leadership, the group selected the major features of the design and settled on a basic feature set and high-order design. At this point, the committee decided to change all the structures to allow for algorithm independence in the specification— this is called algorithm agility. All the authentication techniques were unified with a technique originally called generalized authorization and now called enhanced authorization (EA). This increased the flexibility of authorization while simultaneously reducing the cost of the implementation and reducing the cognitive difficulty of understanding the specification. All objects and entities use the same authentication techniques. Many discussions took place regarding the problems created by having algorithm flexibility while still allowing a user to determine precisely what algorithms were used, both by a given key and also to protect the key, so the overall security of any key held by the TPM could be determined.

When Grawrock left the chairmanship due to changing responsibilities at Intel, Microsoft contributed a full-time editor, David Wooten, and HP took over the chairmanship. It was decided at this point that the specification should be compilable, which drove Wooten to create an emulator while writing the specification. A compilable specification has the advantage of much-reduced ambiguity: if there is doubt about how the specification is supposed to work, it can be compiled into an authoritative emulator. Additionally, the generalized authentication structure was moved from Polish notation (such as used in a TI calculator) to Reverse Polish notation (such as used in an HP calculator), which made implementing the specification easier (but made understanding the specification harder). The committee decided to add multiple key hierarchies to accommodate different user roles.

Wooten worked tirelessly to develop an implementation of the specification and provided strong leadership that drove the specification to its current feature set. When HP's Graeme Proudler stepped down from the chairmanship, David Challener of Johns Hopkins Applied Physics Laboratory formed a joint chairmanship first with Julian Hammersly of AMD, and later with Ari Singer of DMI. Kenneth Goldman (of IBM) took over the editorship from David Wooten after the first release, reprising a role he held for many years with the TPM 1.2 specification.

As new members joined the group over the years and began trying to understand the specification, some of them, notably Will Arthur and Kenneth Goldman, dove deep into the specification line by line. They submitted many bug and readability fixes to the TPM Work Group, and most of those resulted in changes to the specification that enhanced its consistency and readability. Even with these changes, it still is not easy reading, which led to the original impetus for this book.

Summary

The TPM specification has been developed twice. The first time, it developed from 1.1b to 1.2, evolving to incorporate capabilities as they came to be known to the specification committee. This feature-creep form of evolution made the final specification very complicated. In the second generation, TPM 2.0, after the cryptographic weaknesses of SHA-1 caused the need for a change, the architecture was redesigned from scratch— resulting in a much more integrated and unified design. The next chapter introduces the cryptographic concepts that will be used throughout the rest of the book. A good high-level understanding of these is imperative for you to understand TPM 2.0.

 
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