AN3992

Firmware description

Doc ID 022369 Rev 3

11/22

3.4

Key derivation and decryption mode

When this mode is selected, the AES hardware accelerator performs the decryption of a

128-bit cipher text using the provided 128-bit encryption key to compute the plain text. In the

example below, the cipher text is “22 F6 21 81 F8 AF C0 FE 03 36 B8 95 72 CB

D1 A8

" and the encryption key is "ultra-low power.". The plain text, computed by the AES

hardware accelerator, is "STM32L and STM8L".

Figure 5.

AES hardware accelerator: key derivation and decryption mode

0E E5 43 E4 6D 32 44 4D

35 6B 8D 05 4C 22 DF F4

Decryption Key=

"91 DF 30 53 7A E9 49 19

92 FF 8D F8 C4 9B B7 4D”

AES hardware accelerator

decryption mode

128-bit cipher text

CR95HF and STM8L

128-bit cipher text

MS19974V1