Figure 88. Ecb Encryption And Decryption Principle - STMicroelectronics STM32WLEx Reference Manual

RM0461
Note: The chaining mode may be changed only when AES is disabled (bit EN of the AES_CR
register cleared).
Principle of each AES chaining mode is provided in the following subsections.
Detailed information is in dedicated sections, starting from
chaining modes (ECB,
Electronic codebook (ECB) mode
Legend
ECB is the simplest mode of operation. There are no chaining operations, and no special
initialization stage. The message is divided into blocks and each block is encrypted or
decrypted separately.
Note: For decryption, a special key scheduling is required before processing the first block.
CBC).

Figure 88. ECB encryption and decryption principle

Plaintext block 1
key
Encrypt
Ciphertext block 1
Plaintext block 1
key
input
output
key
scheduling
Ciphertext block 1
Encryption
Plaintext block 2
key
Encrypt
Ciphertext block 2
Decryption
Plaintext block 2
key
Decrypt Decrypt
Ciphertext block 2
RM0461 Rev 5
AES hardware accelerator (AES)
Section 21.4.8: AES basic
Plaintext block 3
key
Encrypt
Ciphertext block 3
Plaintext block 3
key
Decrypt
Ciphertext block 3
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