Problem $5(1$ point$).$ An adversary analyzes a sequence of $($ciphertext$)$ characters, which is encrypted by Vigenere Cipher, using Kasishi$$s method. In addition, it knows the key length is at least $2.$ If it can find a sub$-$string $$edlt$,$ which is repeated twice in the sequence, and the distance between the two repeated sub$-$strings is $12,$ what are the possible key length of this Vigenere Cipher?

$2$