MCU-PLUS-SDK-AM243X: SA2UL SHA API Usage and Examples

Bryce Mitchell

Hello,

I am looking at the documentation for the usage of the SA2UL APIs for SHA hashing, as well as the examples in the SDK, and I am not sure of the correct usage. In the documentation here:

AM243x MCU+ SDK: SA2UL (ti.com)

The output buffer given to SA2UL_contextProcess is the size of the resulting hash (e.g. 512 bits or 64 bytes). However in the examples provided in the SDK (e.g. examples\security\crypto\sa2ul_sha\crypto_sha.c), the output buffer is the same size as the input buffer, and the resulting hash is found in gSa2ulCtxObj.computedHash. Which is the intended behavior?

Is it really necessary to include a buffer of the same size as the input even if it's not used when computing the SHA hash? Currently this is the only way I am able to get it to work, but it is wasteful when computing the hash of a large buffer as I have to allocate twice the space for it.

Thank you

over 1 year ago

0 Aakash Kedia over 1 year ago

TI__Mastermind 26145 points

Hi Bryce Mitchell,

In case of pktDMA used with the SHA engine, it will copy the data from src location put it in the SHA engine and put the same data into the destination location.

https://software-dl.ti.com/mcu-plus-sdk/esd/AM243X/latest/exports/docs/api_guide_am243x/SECURITY_SA2UL_MODULE_PAGE.html#Dma_flow

The SHA context will preserve the SHA value.

For better understanding -

Here DMA acts as a copy engine while computing the SHA in parallel. In this architecture, disabling the DMA is not supported, however, in case you want to preserve memory why not give src and destination as same volatile memory so nothing changes in your software and still you get the SHA in your context.

I hope this helps.

Best Regards,
Aakash

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MCU-PLUS-SDK-AM243X: SA2UL SHA API Usage and Examples