Although Dave Oranchak doesn't believe the Zodiac Killer used the scytale method of encryption in the recently decoded 340 cipher, this decryption tool does actually decode the message in the 340 cipher. If the Zodiac Killer responded to the prompt by Dr. Marsh and read Edgar Allan Poe's essay A Few Words on Secret Writing, he would have noticed that the first topic of discussion was the scytale cipher, which involves disguising a message by separation, avoiding the common left-to-right method of decryption. This is what the Zodiac Killer used in his 340 cipher. In further reading of A Few Words on Secret Writing, it became apparent that other encryption methods were discussed in addition to the scytale method, with the possibility existing that the Zodiac Killer may have adopted one of these techniques for his following 13-Symbol cipher on April 20th 1970. The most notable encryption methods discussed included separating the alphabet A to M, and N to Z, into two equal parts of 13 letters. Followed by a technique involving two concentric discs, akin to the Union Cipher Disk that held the number configurations of 000 and 888. These techniques show promise when we consider the design and structure of the 13-Symbol cipher. This has been covered in a much more extensive article, so it will not be covered any further here.
This reminded me of the statement by Dr. Marsh when he challenged Zodiac, who he contended "had not told the truth in his cipher messages to the Examiner, the Chronicle and the Vallejo Times-Herald". He claimed "Zodiac has not done this, because to tell the complete truth in relation to his name would lead to his capture". Did the Zodiac Killer read this passage in A Few Words on Secret Writing and get some ideas?
The reader who mailed Edgar Allan Poe from Stonington, Connecticut, failed to supply his name, but did begin by placing a letter S, followed by a horizontal dash, similar to the Zodiac Killer's introduction on April 20th 1970, The Zodiac Killer began the introduction to his 13-Symbol cipher by stating MY NAME IS ---------. The sender of the cryptograms to Poe only signed his name at the bottom of the intoductory letter by use of initials, concluding with "I am yours, respectfully S.D.L." Not wanting to shy away from the challenge of Dr. Marsh a second time, I couldn't help thinking that the Zodiac Killer may have rose to the challenge and given us the initials to his name (or fictitious initials), just like the sender of the cryptograms from Stonington, Connecticut. Another thing to note, is that Dr. Marsh laid down this challenge on October 22nd 1969, so 182 days had elapsed before the Zodiac Killer's third confirmed cryptogram arrived at the San Francisco Chronicle on April 21st 1970.
That answer could be "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is Fk, I'm crackproof", given to us in the Zodiac Killer's postcard five-and-a-half months later as a big hint to its decipherment. The 340 character cipher was split into rows of 9, 9 and 2 sections. The 13-Symbol cipher may have been split into 2. 2 and 9 sections, with the circled 8's beginning each section of the phrase. The letters K and M were already in place for a perfectly circular message, as highlighted in the October 5th 1970 communication by the Zodiac Killer, in which he supplied us with the phrase Fk I'm crackproof.