ST STM32L0x3 User Manual

RM0367 Rev 7 435/1043
RM0367 AES hardware accelerator (AES)
466
19.4.3 AES cryptographic core
Overview
The AES cryptographic core consists of the following components:
• AES algorithm (AEA)
• key input
• initialization vector (IV) input
The AES core works on 128-bit data blocks (four words) with 128-bit key length. Depending
on the chaining mode, the AES requires zero or one 96-bit initialization vector IV (and a 32-
bit counter field).
The AES features the following modes of operation:
• Mode 1:
Plaintext encryption using a key stored in the AES_KEYRx registers
• Mode 2:
ECB or CBC decryption key preparation. It must be used prior to selecting Mode 3 with
ECB or CBC chaining modes. The key prepared for decryption is stored automatically
in the AES_KEYRx registers. Now the AES peripheral is ready to switch to Mode 3 for
executing data decryption.
• Mode 3:
Ciphertext decryption using a key stored in the AES_KEYRx registers. When ECB and
CBC chaining modes are selected, the key must be prepared beforehand, through
Mode 2.
• Mode 4:
ECB or CBC ciphertext single decryption using the key stored in the AES_KEYRx
registers (the initial key is derived automatically).
Note: Mode 2 and mode 4 are only used when performing ECB and CBC decryption.
When Mode 4 is selected only one decryption can be done, therefore usage of Mode 2 and
Mode 3 is recommended instead.
The operating mode is selected by programming the MODE[1:0] bitfield of the AES_CR
register. It may be done only when the AES peripheral is disabled.
Typical data processing
Typical usage of the AES is described in Section 19.4.4: AES procedure to perform a cipher
operation on page 438.
Note: The outputs of the intermediate AEA stages are never revealed outside the cryptographic
boundary, with the exclusion of the IVI bitfield.
Chaining modes
The following chaining modes are supported by AES, selected through the CHMOD[1:0]
bitfield of the AES_CR register:
• Electronic code book (ECB)
• Cipher block chaining (CBC)
• Counter (CTR)

ST STM32L0x3 Specifications

General

Brand	ST
Model	STM32L0x3
Category	Microcontrollers
Language	English