Embedded Security Subsystem
The Embedded Security Subsystem is nothing but a chip installed on the Thinkpads mainboard that can take care of certain security related tasks confirming to the TCPA standard. It was first introduced among the T23 models and is now under the name Embedded Security Subsystem 2.0 an integral part of most of the modern Thinkpads. The functions of the chip are bound to three main groups:
- public key functions
- trusted boot functions
- initialization and management functions
The purpose of the whole thing is to keep the users sensitive data out of range from software based attacks (like viruses, internet attacks etc.). One way the chip offers to achieve this is by providing storage for keys along with the neccessary functions to handle them within itself, so that a i.e. a private key never has to leave the chip (can't be seen to any piece of software). Besides this there are more complex topics covered by the functionality of the chip. If you want to find out more about it you can find good documents on the IBM Research TCPA resources page.
A linux driver is available, but it's converage of functionality is unknown so far.