[U-Boot] U-Boot RSA en/decryption

[Or Yochanan]

Hello,

This is my first message to the U-Boot mailing list, so please go easy on
me if my syntax is flawed.. ;)

I need to use RSA decryption on my U-Boot, for a specific task i have. In
order to do so - I'd like to use some of the RSA code that have been added
to lib (instead of porting some other encryption code into my environment).

After going over the RSA code, I came to conclusion that the portion of the
code that performs RSA verification using an RSA key (*rsa_verify_key*) is
exactly what I need, since I don't intend to use FIT nor add anything to DT
(it seems like an overkill for my requirements).

However, I fail to understand how to use the RSA's data structures
correctly. Specifically, *rsa_public_key* input parameter requires
arguments that aren't clear to me. I searched online, yet couldn't find any
reference code to parse i.o. to understand what is required from this
struct..

So my main questions are regarding the rsa_public_key struct that is also
mentioned on the documentation:
1. There's a requirement for bot *num-bits*, and *r^2* - how comes? From
what I understand, r^2 can be calculated using num-bits - so currently I
suspect that I got it wrong?
2. What is *n0inverse*? I didn't find anything on the web that explains
this argument, nor did I find anything that resemble the calculation (-1 /
N[0] mod 2^32).

If there's a possibility to better explain these arguments, or even better
- provide a usage example, I'd be grateful.

Thanks in advance,
--
Or