Re: ECC modelling

[Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>]

On Sat, Apr 02, 2011 at 06:33:27PM +0300, Eugene N wrote:
> Thank you very much, Bill
> 
> I will try to understand the scripts you provided (especially one with
> vectors, for i am new to gp syntax). This is very kind of you!
> 
> Unfortunately i installed the older version of pari and am now reinstalling
> the latest one (in mine ffgen was missing).

Ah yes, you need PARI 2.4.3.

> One more question: if i were to generate EC(GF(2^m)) random points, i would
> have to choose random x, solve an equation and obtain corresponding y.

you can use random(E) to get random points on the curve. There is also a function
ellordinate(E,x) which return the possible values for y.

> Does pari provides something for square roots in GF(2^m)?

Yes, you can use sqrt(). However for mathematical reason, you cannot use squareroots to
find ordinate of points on curves in characteristic 2, instead you have to
solve Artin-Shreier equations (see polrootsff).

Cheers,
Bill.