Trying out the

Playfair cipher

despite the fact that K4’s ciphertext is uneven.  Didn’t find much except the word “SCRY”. 

I’m starting to like the idea of an uneven fractionating cipher system followed by a transposition for the enciphering system used on K4.  The decryption would be the reverse, just to be clear.

Still, Playfair is not entirely unrealistic, especially if I’m wrong.