Correct
以子之矛，攻子之盾
/ yǐ zǐ zhī máo, gōng zǐ zhī dùn /
Strokes
Definition
lit. use sb's spear to attack his shield (idiom, derived from Han Feizi 韩非子); turning a weapon against its owner/fig. to attack an opponent using his own devices/hoist with his own petard
Example
Definition
set a person's own spear against his own shield—refute sb with his own argument