$4\mathrm{.}6$ Suppose the DES F function mapped every $32-$bit input $R,$ regardless of the value of

the input $K,$ to

a$.$ a $32-$bit string of zero, and

b$.R.$

Then:

What function would DES compute?

What would the decryption look like?

Hint: Use the following properties of the XOR operation:

$(Ao+B)o+C=Ao+(Bo+C)$

$4\mathrm{.}6/$ KEY TERMS, REVIEW QUESTIONS, AND PROBLEMS

$(Ao+A)=0$

$(Ao+0)=A$

$Ao+1=$ bitwise complement of $A$