I have a current project that uses ECDH from this embedded library and was hoping to get your library to talk to it.

https://github.com/kmackay/micro-ecc

Ironically it uses different key sizes, exact opposite as your library.

Public Key (64 bytes)
Private Key (32 bytes)

I believe it's due to the way the github library defaulted. I am not familiar enough with the algorithm to know, in all the places you have a hard coded in size, how much would get corrupted by making the change and if the hash etc belongs to one of the key sizes.

Is it possible to wrap your sizes in a const () at the top, and make it easily changable ?