# Trusted Platform Module

Trusted Platform Module (TPM) is an international standard for a secure cryptoprocessor, which is a dedicated microprocessor designed to secure hardware by integrating cryptographic keys into devices.

In practice a TPM can be used for various different security applications such as secure boot and key storage.

TPM is naturally supported only on devices that have TPM hardware support. If your hardware has TPM support but it is not showing up, it might need to be enabled in the BIOS settings.

## Drivers

TPM drivers are natively supported in modern kernels, but might need to be loaded:

    # modprobe tpm

Depending on your chipset, you might also need to load one of the following:

    # modprobe tpm_atmel tpm_bios tpm_infineon tpm_nsc tpm_tis

## Usage

TPM is managed by `tcsd`, a userspace daemon that manages Trusted Computing resources and should be (according to the TSS spec) the only portal to the TPM device driver. `tcsd` is part of the trousersAUR AUR package, which was created and released by IBM, and can be configured via `/etc/tcsd.conf`.

To start tcsd and watch the output, run:

    # tcsd -f

or simply start and enable `tcsd.service`.

Once `tcsd` is running you might also want to install tpm-toolsAUR which provides many of the command line tools for managing the TPM.

Some other tools of interest:

- tpmmanager — A Qt front-end to tpm-tools

  http://sourceforge.net/projects/tpmmanager || tpmmanagerAUR

- openssl_tpm_engine — OpenSSL engine which interfaces with the TSS API

  http://sourceforge.net/projects/trousers || openssl_tpm_engineAUR

- tpm_keyring2 — A key manager for TPM based eCryptfs keys

  http://sourceforge.net/projects/trousers || tpm_keyring2AUR

- opencryptoki — A PKCS#11 implementation for Linux. It includes drivers and libraries to enable IBM cryptographic hardware as well as a software token for testing.

  http://sourceforge.net/projects/opencryptoki || opencryptokiAUR

### Basics

Start off by getting basic version info:

    $ tpm_version

and running a selftest:

    $ tpm_selftest
     TPM Test Results: 00000000

### Securing SSH Keys

There are several methods to use TPM to secure keys, but here we show a simple method based on simple-tpm-pk11-gitAUR.

First, create a new directory and generate the key:

    $ mkdir ~/.simple-tpm-pk11
    $ stpm-keygen -o ~/.simple-tpm-pk11/my.key

Point the config to the key:

    ~/.simple-tpm-pk11/config

    key my.key

Now configure SSH to use the right PKCS11 provider:

    ~/.ssh/config

    Host *
        PKCS11Provider /usr/lib/libsimple-tpm-pk11.so

It's now possible to generate keys with the PKCS11 provider:

    $ ssh-keygen -D /usr/lib/libsimple-tpm-pk11.so

Note: This method currently does not allow for multiple keys to be generated and used.

## References

- TPM on Wikipedia
- Embedded Security Subsystem on Thinkwiki
- TPM Fundamentals (PDF)

Categories:

- Security
- Other hardware