Figure 4. Example of peripheral device authentication

Local Host

Peripheral or consumable

STSAFE-A120

I2C

1. Read certificate

X509 public key certificate

Verifies

peripheral’s public

key certificate

Generates

challenge

2. Generate signature

Signature

Verifies

signature

2.2

Applicative data storage

The STSAFE-A120 comes with 16 Kbytes of nonvolatile memory configurable by the customer for its application

data storage. These 16 Kbytes must be partitioned into zones with the appropriate access rights.

Some of the zones can be configured into secure one-way counters (decrementing) zones with associated data

space.

The access condition to the memory zones can be configured as well for each zone. The access condition can

be:

•

Free access

•

Host secure channel access

•

Entity authentication access

•

Host secure channel and entity authentication access.

2.3

Local envelope wrapping/unwrapping

The STSAFE-A120 offers a data wrapping service (cyphering and signing data) into a secure envelope. This

service is intended to be used by a host to store sensitive information in a non protected memory. This envelope

can be unwrapped (unciphered and verified) at anytime by the STSAFE-A120.

Figure 5. General principle of the wrapping/unwrapping key

Wrapping

Envelope

Unwrapping

Secret/plain text

Local envelope key

Secret/plain text MAC

Secret/plain text

Wrapping is the mechanism used to protect a secret or plain text (like connectivity keys or credentials). The

output of the wrapping is an envelope.

The envelope consists of the secret or plain text to be protected, encrypted with an AES key wrap algorithm. The

algorithm uses a local envelope key for a local envelope. The envelope also contains the MAC of the encrypted

key or plain text to authenticate the envelope.

Unwrapping is the mechanism used to decrypt the envelope and recover the secret or plain text.

STSAFE-A120

Product use cases

DS14609 - Rev 1

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