以子之矛，攻子之盾 yǐ zǐ zhī máo, gōng zǐ zhī dùn

yǐ zǐ zhī máo, gōng zǐ zhī dùn phrase use sb's spear to attack his shield (idiom, derived from Han Feizi 韓非子|韩非子); turning a weapon against its owner; to attack an opponent using his own devices
Domain: Modern Chinese 现代汉语 , Subdomain: Military
Notes: (CC-CEDICT '以子之矛，攻子之盾')