wàn néng yào shi
master key
skeleton key
passkey
yī bǎ yào shi kāi yī bǎ suǒ
One key opens one lock.
There is a different solution for each problem. (idiom)
gōng kāi yào shi
public key (in encryption)
sī rén yào shi
private key (in encryption)
xiàn zài shì guò qu yào shi
Today is the key to the past.