SPIRIT1 datasheet(42/94 Pages) STMICROELECTRONICS

42 / 94 page

Block description

SPIRIT1

42/94

Doc ID 022758 Rev 3

Two output modes are available: buffered or not buffered (high output impedance, about 100

Ω). The latter mode is the default one.

The TS function is available in every operating mode. When enabled, the internal logic

allows the switching on of all the necessary circuitry.

To enable the TS function, the user must perform the following operations:

●

Set to 1 the TS bit in the ANA_FUNC_CONF[0] register

●

Program as “Analog” (00) the GPIO_MODE field in the GPIO0_CONF register (other

fields are neglected)

●

Optionally, enable the buffered mode (the EN_TS_BUFFER bit in the PM_CONFIG[2]

As the TS function requires the internal bias circuit operation, the overall current

consumption in STANDBY, SLEEP, and READY modes is increased by 400 µA.

8.11

AES encryption co-processor

The SPIRIT1 provides data security support as it embeds an advanced encryption standard

(AES) core which implements a cryptographic algorithm in compliance with NIST FIPS 197.

Three registers are available to use the AES engine of SPIRIT1:

●

AES_KEY_IN [15:0]: R/W type register (128-bit), used to provide the key to use

●

AES_DATA_IN [15:0]: R/W type register (128-bit), used to provide the input to the AES

engine

●

AES_DATA_OUT [15:0]: R type register (128-bit), used to retrieve the output of the AES

operation.

The core processes 128-bit data blocks using 128-bit keys.

The AES can be accessed in any of the SPIRIT1 operation modes.

To turn on the AES engine, the AES_ON bit in the ANA_FUNC_CONF[0] register must be

set.

Once the AES engine is on, it processes the operations according to the commands sent.

The SPIRIT1 engine provides 4 different operations:

Encryption using a given encryption key (AES Enc command). In this operation, the

MCU puts the encryption key into the AES_KEY_IN[15:0] register and the data to

encrypt into the AES_DATA_IN[15:0]. The MCU sends the AES Enc command and

when the AES_EOP (end of operation) is issued, the MCU can retrieve the data

encrypted from AES_DATA_OUT[15:0]

Decryption key derivation starting from an encryption key (AES Key command). In this

operation, the MCU puts the encryption key into AES_DATA_IN[15:0]. The MCU sends

the AES Key command and when the AES_EOP (end of operation) is issued, the MCU

can retrieve the decryption key from AES_DATA_OUT[15:0]

Data decryption using a decryption key (AES Dec command). In this operation, the

MCU puts the decryption key into the AES_KEY_IN[15:0] register and the data to

decrypt into AES_DATA_IN[15:0]. The MCU sends the AES Dec command and when

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