ST STM32L0x3 User Manual

AES hardware accelerator (AES) RM0367
444/1043 RM0367 Rev 7
output data block Cx. The ECB encryption continues in this way until the last complete
plaintext block is encrypted.
Figure 92 illustrates the electronic codebook (ECB) decryption.
Figure 92. ECB decryption
To perform an AES decryption in the ECB mode, the secret key has to be prepared by
collecting the last-round encryption key (which requires to first execute the complete key
schedule for encryption), and using it as the first-round key for the decryption of the
ciphertext. This preparation is supported by the AES core.
In ECB decrypt mode, the 128-bit ciphertext input data block C1 in the AES_DINR register
first goes through bit/byte/half-word swapping. The keying sequence is reversed compared
to that of the ECB encryption. The swap result I1 is processed with the AES core set in
decrypt mode, using the formerly prepared decryption key. The decryption result goes
through bit/byte/half-word swapping, then is stored in the AES_DOUTR register as 128-bit
plaintext output data block P1. The ECB decryption continues in this way until the last
complete ciphertext block is decrypted.
Figure 93 illustrates the cipher block chaining (CBC) encryption mode.
Figure 93. CBC encryption
In CBC encrypt mode, the first plaintext input block, after bit/byte/half-word swapping (P1’),
is XOR-ed with a 128-bit IVI bitfield (initialization vector and counter), producing the I1 input
data for encrypt with the AES core, using a 128- key. The resulting 128-bit output block O1,
after swapping operation, is used as ciphertext C1. The O1 data is then XOR-ed with the
MSv19106V2
Decrypt
AES_KEYRx (KEY)
AES_DINR (ciphertext C1)
AES_DOUTR (plaintext P1)
Swap
management
DATATYPE[1:0]
DATATYPE[1:0]
Swap
management
Decrypt
AES_KEYRx (KEY)
AES_DINR (ciphertext C2)
AES_DOUTR (plaintext P2)
Swap
management
DATATYPE[1:0]
DATATYPE[1:0]
Swap
management
input
output
Legend
I1 I2
O1 O2
Block 1 Block 2
MSv19107V2
Block cipher
encryption
AES_KEYRx (KEY)
AES_DINR (plaintext P1)
AES_DOUTR (ciphertext C1)
Swap
management
DATATYPE[1:0]
DATATYPE[1:0]
Swap
management
Block cipher
encryption
AES_KEYRx (KEY)
AES_DINR (plaintext P2)
AES_DOUTR (ciphertext C2)
Swap
management
DATATYPE[1:0]
DATATYPE[1:0]
Swap
management
AES_IVRx (init. vector)
input
output
Legend
XOR
I1
I2
O1
O2
Block 1 Block 2
IVI
P1'
P2'

ST STM32L0x3 Specifications

General

Brand	ST
Model	STM32L0x3
Category	Microcontrollers
Language	English