Bill Allombert on Sun, 09 Dec 2007 20:16:46 +0100

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Re: FFELT: how to recover the field?

On Sun, Dec 09, 2007 at 05:03:52PM +0100, Bill Allombert wrote:
> On Sun, Dec 09, 2007 at 04:15:46PM +0100, Jeroen Demeyer wrote:
> > Hello list,
> > 
> > Given a FFELT x in characteristic p, I would like to compute a p-th root 
> > of x.  The most obvious way to do this is to compute x^(p^(n-1)), where 
> Why are sqrtn(x,p) and x^(1/p) less obvious ?
> > p^n is the cardinality of the field.  However, how can I recover p and n 
> > given only the FFELT?  Obviously, it suffices to get the polynomial 
> > defining the finite field (i.e. the argument given to ffgen()).  I tried 
> > x.mod, but that doesn't work.
> I think x.mod should be made to work, but I did not implement it because
> I was not sure whether x.mod should return a polynomial with t_INT or
> t_INTMOD coefficients (mod p).

Done in CVS.

I decided to return t_INT coefficient, since that closer to the internal
representation and .mod is a member function.