Bill Allombert on Sun, 09 Dec 2007 17:36:51 +0100 |
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Re: FFELT: how to recover the field? |
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). In the mean time, you can use n=poldegree(charpoly(0*a)). You can get p using x.p. Thanks for your input, Bill.