Table 137. Initialization Of Aes_Ivrx Registers In Ccm Mode; Figure 123. Ccm Mode Authenticated Encryption - ST STM32WL5 Series Reference Manual

RM0453
CCM processing
Figure 123
example). This mode is selected by writing 100 into the CHMOD[2:0] bitfield of the AES_CR
register.
(1) Init
AES_IVRx (CTR0)
mask
AES_IVRx (First block B0)
Encrypt
AES_KEYRx (KEY)
(2) Header
AES_DINR (associated
data block B1)
Swap
management
DATATYPE[1:0]
Encrypt
AES_KEYRx (KEY)
Legend
input
output
XOR
The data input to the generation-encryption process are a valid nonce, a valid payload
string, and a valid associated data string, all properly formatted. The CBC chaining
mechanism is applied to the formatted plaintext data to generate a MAC, with a known
length. Counter mode encryption that requires a sufficiently long sequence of counter blocks
as input, is applied to the payload string and separately to the MAC. The resulting ciphertext
C is the output of the generation-encryption process on plaintext P.
AES_IVRx registers are used for processing each data block, AES automatically
incrementing the CTR counter with a bit length defined by the first block B0.
shows how the application must load the B0 data.
Note: The AES peripheral in CCM mode supports counters up to 64 bits, as specified by NIST.
Register
Input data
describes the CCM implementation within the AES peripheral (encryption

Figure 123. CCM mode authenticated encryption

Counter
increment (+1)
AES_KEYRx (KEY)
AES_DINR (plaintext P1)
Swap
management
AES_DINR (associated
data last block Bu)
Swap
management
DATATYPE[1:0]
Encrypt
AES_KEYRx (KEY)

Table 137. Initialization of AES_IVRx registers in CCM mode

AES_IVR3[31:0]
B0[31:0]
Block 1
AES_IVRx (CTR1)
Encrypt
S1
DATATYPE
[1:0]
DATATYPE
[1:0]
Swap
management
AES_DOUTR (ciphertext C1)
B
u+1
Encrypt
AES_KEYRx (KEY)
AES_IVR2[31:0]
B0[63:32]
RM0453 Rev 1
AES hardware accelerator (AES)
(3) Payload
AES_IVRx (CTRm)
Counter
increment (+1)
AES_KEYRx (KEY)
AES_DINR (plaintext
last block Pm )
DATATYPE
Swap
[1:0]
management
DATATYPE
[1:0]
(ciphertext last block Cm)
AES_KEYRx (KEY)
AES_DINR (CTR0)
S0
Encrypt
AES_DOUTR
AES_KEYRx (KEY)
Table 137
AES_IVR1[31:0] AES_IVR0[31:0]
B0[95:64]
Block m
Encrypt
Sm
Swap
management
AES_DOUTR
B
r
Encrypt
MAC (T)
(EncTAG)
(4) Final
MSv42152V2
B0[127:96]
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