Consider private key crypto-system has $3$ keys, $3$ plain-texts and $4$ cipher-texts:
$K=\{ k1,k2,k3 \}$
$M=\{m1, m2,m3 \}$
$C=\{c1,c2,c3,c4 \}$
In a valid encryption table find the key that maps two different messages to same cipher text:
- k1
- k2
- k3
- No key can map