We present a polynomial time Monte-Carlo algorithm for finite simple black
box classical groups of odd characteristic which constructs all root
${\rm{SL}}_2(q)$-subgroups associated with the nodes of the extended Dynkin
diagram of the corresponding algebraic group.
We present a one sided Monte--Carlo algorithm which constructs a long root
$\sl_2(q)$-subgroup in $X/O_p(X)$, where $X$ is a black-box group and
$X/O_p(X)$ is a finite simple group of Lie type defined over a field of odd
order $q=p^k > 3$ for some $k\geqslant 1$. Our algorithm is based on the
analysis of the structure of centralizers of involutions and can be viewed as a
computational version of Aschbacher's Classical Involution Theorem.