以子之矛，攻子之盾

yǐ zǐ zhī máo , gōng zǐ zhī dùnyizizhimao,gongzizhidun

1. lit. 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
2. fig. to attack an opponent using his own devices
3. hoist with his own petard

Study it in Yanamino