The secret code behind the CIA's Kryptos puzzle is up for sale

I've spent a fair amount of time on K4, and my conclusion is that it's simply a poor puzzle. At this point 24 of 97 characters have been revealed, and yet there's seemingly still not enough information pointing to how the known plaintext corresponds to the ciphertext. Over the decades everything reasonable has been tried and eliminated, which means the solution is likely to be unreasonable.

I have discovered a truly marvelous solution to this code, which this text box is too small to contain.

And the secret key is: puppy