I'm implementing arithmetics for elliptic curves over secp256r1 as a homework assignment.

For scalar multiplication, the assignment specifically specifies that $k$ is "any hexidecimal encoded integer" (for the multiplication $kP$).

How is multiplication defined for negative values of $k$? My best guess is that $k$ is calculated modulo #$E(\mathbb{F}_p)$, which in this case is $nh$ (the cardinality of the group of the points on the curve) as specified by SEC (in http://www.secg.org/download/aid-386/sec2_final.pdf). Is that correct?

If not, how is scalar multiplication defined for negative $k$'s?