Recall the meet$-$in$-$the$-$middle attack on double DES discussed in this chapter. Assuming that chosen plaintext is available, this attack recovers a $112-$bit key with about the same work needed for an exhaustive search to recover a $56-$bit key, that is$,$ about $255.$

If we only have known plaintext available, not chosen plaintext, what changes do we need to make to the double DES attack?

What is the work factor for the known plaintext version of the meet$-$in$-$the$-$middle double DES attack?