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Home arrow Computer Science arrow A Practical Guide to TPM 2.0
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TPM Administration and WMI

Windows exposes many common TPM administrative tasks through GUI tools and through a scriptable and remote programming interface called Windows Management Instrumentation (WMI). This interface lets an administrator switch on TPMs, clear them, disable them, and so on. It transparently supports both TPM 1.2 and TPM 2.0.

The Platform Crypto Provider

Most Windows programs use cryptography through a set of interfaces called Cryptography Next Generation (CNG). CNG provides a uniform library for performing both software-based and hardware (such as High Security Module) based cryptography. Windows 8 lets you specify the TPM as a key protector for a subset of TPM-supported cryptography by specifying use of the Platform Crypto Provider. The Platform Crypto Provider has been extended to include a few specific TPM-like behaviors, such as quoting and key certification.

Virtual Smart Card

Windows 8 further extracts the TPM to behave like a smart card in any and all cases where a smart card can be used. This includes both enterprise and web logon.

Applications That Use TPMs

Table 4-1 lists applications that are currently available that use the TPM, along with the interface they use and the OS on which they run. All these work with TPM 1.2. Some of them, as noted, also work with TPM 2.0.

Table 4-1. Applications and SDKs That Use TPMs, by Interface and OS

Table 4-1. (continued)

As the table demonstrates, many applications use TPMs. There are even some large companies that use them. [1] BitLocker is one of the most widely used of these programs that use extended capabilities of the TPM. Wave Systems Embassy Suite is another. Often, conflicting management software requires multiple TPM programs to be used on the same system.

With a 1.2 TPM, there was a single storage root key (SRK), which had to have an authorization that was shared by all applications using the TPM. Unfortunately, there was not unanimity in how to create the SRK—it could be created without needing any authentication, needing only a well-known secret of 20 bytes of 0, or needing the hash of a well-known secret for its password. Additionally, there was an owner authorization that was somewhat sensitive, because it was used to reset the dictionary attack mechanism as well as reset the TPM or create an attestation key (thought by some to be privacy sensitive).

Unfortunately, the owner authorization was also used to authorize allocation of non-volatile RAM space, which meant applications that needed to allocate nonvolatile RAM space had to know it. But if a different application took ownership of the TPM and set the owner authorization to a random number, protected by a back-end management function, it was unknown even to the end user. Some applications did this. If applications did not know how to coordinate with that back-end management application, they could not function.

The result was that the user was restricted to using a single suite of applications with the TPM, in order to allow all applications to have access to the authorizations they needed. In practice, this meant software that directly used the TPM had to be from the same developer as the management software used to set up the TPM.

This issue was somewhat mitigated when using only PKCS #11 or MS CAPI enabled applications, because they only required that there be a single application for managing the TPM; but they also couldn't use the higher functions of the TPM, such as attestation. This problem seems to be gradually disappearing. For example, Wave Systems software can manage TPMs for attestation and also for BitLocker.

TPM 2.0 still requires some coordination for authorization; but it lets you use multiple SRKs with the TPM, allowing completely separate applications to use the TPM with less coordination.

In researching applications that use the TPM, most of the use cases that come quickly to mind are supported by commercial software. However, some obvious use cases for software that uses a TPM, don't seem to exist in the marketplace.

  • [1] See Ellen Messmer, Network World (2010), “PwC Lauds Trusted Platform Module for Strong Authentication,” networkworld.com/news/2010/091510-trusted-platform- authentication.html.
 
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