I’ve been looking for a likely candidate to try out decrypting my potentially un-superenciphered Kryptos K4 strings.

Is it foursquare?

I don’t really know, it makes more sense than bifid (can’t use transposition) and more likely than playfair (insertion of null characters with doubles) plus it gives the chance to have 2 keywords and it’s a matrix based substitution cipher.

I’ll give it a shot with the plaintext break BERLIN.