KEY EQUIVOCATION AND NOMINAL UNICITY POINT

Suppose we have an alphabet of $6$ letters ABCDEF. Suppose these letters appear

in messages uniformly at random $($i$.$e$.$ independently, with equal probability$).$

Consider a general monoalphabet cipher on this alphabet, with key chosen uni$-$

formly at random.

Compute the key equivocation for ciphertexts of length $3,6,$ and $12.$

Compute the nominal unicity point for this cipher. Why is this result of no

practical use?