Does anyone know if anyone has done an implementation of secq [*] in code? I'm pretty sure not, but asking just in case.

I can ( and probably will) just do it in python (literally just swap p and N), it'll let me play with algos but 100% useless for anything real. Needs optimised algorithms, even if you ignored constant time implementation.

[*] secq256k1 is a kind of 'mirror' version of the secp256k1 that we use in bitcoin. The curve group order of secq is the finite field order of secp and vice versa. It's some kind of very deep fact that such 'mirror pairs' of elliptic curves of prime order are much more common than you would expect by chance. Why care? It makes something similar to merkle trees be possible using curve points, which is remarkably powerful.