When DES is used with a weak key K$,$ then EK $($EK $($p$))=$ p$.$

When we use a pair of keys K$1,$ K$2,$ with K$1=$ K$2,$ such that EK$1($EK$2($p$))=$ p$,$ then such keys are

known as semi$-$weak keysWhen DES is used with a weak key K$,$ then EK $($EK $($p$))=$ p$.$

When we use a pair of keys K$1,$ K$2,$ with K$1=$ K$2,$ such that EK$1($EK$2($p$))=$ p$,$ then such keys are

known as semi$-$weak keys