Application setup

AN3992

16/22

Doc ID 022369 Rev 3

4.7

Using the software implementation of AES chaining modes

This firmware example both encrypts and decrypts the memory contents of a contactless tag.

The plain text is read from the contactless tag and encrypted by using the AES hardware

included in the STM8L162M8 device. The cipher text is sent to the CR95HF through the SPI

bus and transmitted to the contactless tag.

The encryption and decryption keys are stored in the EEPROM data of the STM8L162M8

device.

Figure 9 presents the main functions.

Figure 9.

Application flow chart

MS19973V1

Start

END

Display on hyper terminal (1)

Initialize Contactless tag

Display on hyper terminal (2)

Display on hyper terminal (3)

Is a tag present?

No

Yes

Read 128 bits from tag

Display on hyper terminal (4)

Write the cypher text

Read the cypher text

Display on hyper terminal (5)

Decrypt

Encrypt

Is a tag present?

No

Yes