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Home arrow Computer Science arrow A Practical Guide to TPM 2.0
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TSS.Net and TSS.C++

Windows 8 and TPM 2.0 were released before there were standards for TPM programming. To fill this gap, Microsoft developed and open sourced two libraries that let application programmers develop more complicated TPM-based applications than CNG or virtual smart cards allowed.

TSS.Net and TSS.C++ provide a thin veneer over TPM 2.0 for both managed code (such as C#) and native code (C++) applications. Both libraries allow applications to be built for a real TPM device (on TBS) or a TPM simulator (over a TCP/IP network connection.)

Although the TSS.Net and TSS.C++ libraries are low level, the authors have made every effort to make programming the TPM easy. For instance, here is a complete program for obtaining random numbers from the TPM:

void GetRandomTbs()

{ // Create a TpmDevice object and attach it to the TPM. Here you

// use the Windows TPM Base Services OS interface. TpmTbsDevice device;

if (!device.Connect()) {cerr << "Could not connect to the TPM device"; return;}

// Create a Tpm2 object "on top" of the device. Tpm2 tpm(device);

// Get 20 bytes of random data from std::vector<BYTE> rand = tpm.GetRandom(20);

// Print it out.cout << "Random bytes: " << rand << endl; return;}

All of these interfaces work, but of course some, such as TBS, are specific to the Windows OS. If you want to write programs that are portable to other OSs, you are better off with one of the others. For TPM 1.2, TSS was the interface with the broadest OS adoption. The next section considers an application that was written using TSS to take advantage of advanced TPM functions.

Wave Systems Embassy Suite

Wave Systems has written software to a TPM-specific interface, rather than to a higher-level interface such as PKCS #11. It needed to be done that way, to take advantage of the TPM's attestation capabilities. Because these capabilities aren't addressed in any other crypto-coprocessor, they aren't available in standard interfaces such as PKCS #11. Wave Systems uses the TCG TSS interface implemented in TrouSerS to talk to the TPM, manage the TPM owner password, create attestation identity keys (AIKs), and attest to those values via a standard called Trusted Network Connect, which communicates back to an administrative server. This server notices when PCR values have changed, and it can send alerts to IT staff when that happens. Some PCRs (like 0, which represents the BIOS firmware) should not change, unless the BIOS of a device has been upgraded, an event that IT should be aware of. TSS 1.2 was available for Windows, Linux, Solaris, BSD, and even the MAC OS. TSS 2.0 will be a good selection for the same reasons, if you want to be able to port your code to other OSs.

TSS 2.0 has been designed specifically with the aim of making programming TPM 2.0 as easy as possible. It is designed in layers so that at the lowest level, direct access to the TPM is still possible. Common design patterns that use a cryptographic coprocessor are made particularly easy to use at the highest application level programming interface. However, there are still some ground rules that every application developer should remember when developing applications that use a TPM.

 
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