The Zodiac Killer responded on November 8th 1969 by using the scytale method of decryption featured at the top of Poe's essay A Few Words On Secret Writing. Or should I say, it can be used to crack the 340 cipher encrypted message, that contained the wording "one in paradice" just like Edgar Allen Poe's poem to his dead wife entitled "To One In Paradise". The next method of encryption in Poe's A Few Words On Secret Writing involved splitting the alphabet A to M and N to Z (two sections of thirteen) mirroring the Zodiac's 13 character code which began with A and ended with M - and because of the distinct lack of characters in this code - it has been considered unsolvable using standard cryptographic methods.
The Zodiac seemingly didn't supply us with a key to this code in later communications, leading me to believe that the key or answer lies in the Edgar Allen Poe essay mentioned above. I believe the answer to the code is "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is....Fk, I'm crackproof, in which each element of the phrase is begun by each of the circled eights, thereby creating an infinite circular cipher (hence the circled 8's which represent infinity and a new beginning). The Zodiac Killer may have supplied us with the answer to the Z13 code in the 13-Hole postcard on October 5th 1970 in which he configured the punched holes in an arrangement of 10 to 3, pinpointing the position of the three eights, and supplying the answer of Fk, I'm crackproof. Using Edgar Allen Poe's reasoning in A Few Words On Secret Writing, I can now place five letters in the correct position within the 13 character code, albeit not to my complete satisfaction.