Re: What's the code for doing the reverse of this code over the altbn128 curve

[Aurel Page <aurel.page@normalesup.org>]

    This has nothing to do with the order of points, it simply
    identifies elements of F_p(w) that are in fact in F_p(i), and
    applies this to the coordinates of the points.
    
    Aurel

On 18/07/2025 16:12, Laël Cellier wrote:

Thank you, and this would work with any point having the correct order ? or would this work only with points having coordinate withing specific bounds ?

Dear Laël,

What you are looking for is ffinvmap:

? mapi = ffinvmap(map);
? twisti(pt) = [ffmap(mapi,pt[1]/w^2), ffmap(mapi,pt[2]/w^3)];
? pt3 = twisti(pt2);
? pt3 == pt
%15 = 1

Cheers,
Aurel