STSAFE-A110 datasheet(17/36 Pages) STMICROELECTRONICS

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STSAFE-A110

Pairing with a local host

To protect and authenticate the link between the STSAFE-A110 and the local host, some

secure channel protocols using symmetric cryptography have been put in place, namely the

host secure channel.

Figure 9. Host and Admin secure channels

The host secure channel protocol protects the link between a local host and the STSAFE-

A110 chip; it constitutes a kind of pairing. It is based on a set of four mechanisms using two

symmetric keys, the so-called host keys. These keys are used to MAC the commands (C-

MAC) and respective responses (R-MAC). They are also used to encrypt the commands

and their respective response to avoid eavesdropping.

3.1

Host secure channel setup use case

In order to execute some specific commands requiring a C-MAC, the local host needs to

generate a Host MAC key and a Host cipher key. It puts these keys into the STSAFE-A110’s

Host key slots.

The PUTATTRIBUTE command is used to input the keys into the STSAFE-A110. It is a free

command until the slots are populated.

The DELETEKEY command deletes the keys. This command requires the Admin secure

channel.

Command flow

This use case assumes that the slots are empty, and cannot be implemented a second time

without first deleting the keys present in the slots.

This operation shall be performed in a secure environment, such as the customer

manufacturing plant.

The local host requests the STSAFE-A110 to generate a 128-bit random to be used as

the host C-MAC key.

The local host requests the STSAFE-A110 to generate a 128-bit random to be used as

the host cipher key.

The local host sends the PUT ATTRIBUTE command for the “Host key slot” attribute,

together with the two generated keys (forming a 256-bit payload).

The STSAFE-A110 chip stores the keys into their respective slots and returns a

successful response.

The local host stores the host C-MAC & cipher keys to a secure area.

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