Request for AES CBC support in mbedtls version 3.1.0

[sandeepacharya2]

Suggested enhancement

I am looking at supporting odd block sizes such as 17, for this i would need MBEDTLS to support the CBC mode in functions such as mbedtls_aes_cmac_prf_128

Justification

This is needed to support features such as UWB FiRa STS generation as per the FiRa specification version 2.0

Mbed TLS needs this because it can be thereby used in applications such as UWB for Crypto

[gilles-peskine-arm]

I'm sorry, I don't understand the feature you're requesting. Mbed TLS does support AES-CBC. The AES block size is always 16, and I don't know what number could be called “block size” and could be 17. I'm not familiar with FIRa, can you point to the precise specification?

[sandeepacharya2]

@gilles-peskine-arm AES-CBC for odd block sizes which are not multiples of 16, must support the XOR operation after the first block.
Similar to AES ECB mode, there needs to be a function to handle AES-CBC similar to mbedtls_aes_cmac_prf_128

[gilles-peskine-arm]

I'm sorry, I still don't understand what you're asking for. The block size of AES-CBC is 16, it isn't a configurable parameter. Can you please give us a precise specification? Note that we don't have access to FIRa specifications that are behind a paywall.