AES-128-CTR using SAES through MCUboot is slower than software on STM32H533 — is this expected?

[parato]

Hello,

I am evaluating cryptographic performance for a secure boot using a NUCLEO-H533RE board and the OEMiRoT example from STM32CubeH5.

I compared two AES-128-CTR implementations:

• Software: mbedtls_aes_crypt_ctr().
• Hardware-backed: bootutil_aes_ctr_encrypt() using SAES.

The mean encryption times are:

Input size	Software	SAES-backed implementation
32 bytes	10.55 µs	29.46 µs
256 bytes	76.70 µs	222.88 µs
1024 bytes	303.50 µs	886.02 µs

 

For an academic comparison, is it accurate to describe this result as “software AES-CTR versus SAES ECB with software CTR and driver protection overhead”?

 

Thank you!