Figure 103. Cbc Encryption And Decryption Principle - STMicroelectronics STM32WL5 Series Reference Manual

RM0453
Cipher block chaining (CBC) mode
Legend
In CBC mode the output of each block chains with the input of the following block. To make
each message unique, an initialization vector is used during the first block processing.
Note: For decryption, a special key scheduling is required before processing the first block.

Figure 103. CBC encryption and decryption principle

Plaintext block 1
initialization
vector
key
Encrypt
Ciphertext block 1
Plaintext block 1
initialization
vector
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
RM0453 Rev 5
AES hardware accelerator (AES)
Plaintext block 3
key
Encrypt
Ciphertext block 3
Plaintext block 3
key
Decrypt
Ciphertext block 3
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