Kudos Dave, guys. Real deal. Amazing job.
“Nobody called him Arthur.”
WOWOWOWOW
Congratulations to Dave Oranchak, Jarlve and Sam.
Incredible! Thanks to the 340 I have (for better or worse) turned into a serious crypto enthusiast over the last few years, following closely everyone here on the board. It has been a companion during late nights and long quarantine days and lunch hours at work. This solution feels totally right, and to echo others here – is clear, fits the timeline, the language, etc. It’s basically self-confirming in it’s plaintext details. It is a simple transposition with a couple of quirks and misspellings – just enough to keep codebreakers off the scent.
To take nothing away from the crew – it almost leaves me surprised it was not cracked earlier – but of course I can see too that there were rock solid leads like period 19 that just took time to fully suss out. Almost hilarious that it begins with "I" and has plaintext words of "Life" and "Death".
I have been working (a bit obsessively) on the 340 for the last few years using pen and paper of a sort. I am really excited to look at my own work in the light of the solution. I might post some of that work too if I notice anything interesting, curious or useful. Off the bat I can say I feel like I was onto the last two lines being separate from the previous parts of the text… As well as the sense that the text was fairly repetitive…Can’t wait to dig in again with this new perspective!
Cheers again!
Thanks everyone for the positive sentiment.
Quicktrader true to form. <3
daikon, very nice to hear from you one more time! You are a legend.
A few months ago, I had a discussion with Dave on Reddit (with a different screen name) in which I said math alone wasn’t going to solve the 340, it’s going to take a psychological solve. The next thing you know, Dave’s making choices because things like gas chamber are appearing in possible solutions.
I like to think that’s my small part in all of this. 
It’s certainly not the math.
I’ve been reading a lot of the articles and comments on various sites about this. If I have to read even ONE MORE "Ted Cruz" or "Ovaltine" joke, I’m going to start throwing things!!!
LOL.
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I don’t believe in monsters.
Congratulations to those who deciphered the 340.
A couple of odd choices (or perhaps errors) Z made based on solution observations
It would appear that he either a. Did not independently factor a substitution for the letter K or b. Decided to use the fully colored in circle for both K and V. This seems like an odd error to make seeing as it was the only such letter throughout and assuming he would have made a key for every letter in the plaintext.
Secondly when thinking of frequency most of the commonly frequent letters in the english alphabet were properly substitution coded to allow variance. As in E had 6 substitution variables, A had 5 etc. Based on this though it seems odd that the letters C and H only had 1 single symbol substitution despite appearing at a higher frequency. The H especially being seen 20 times and only ever substituted with the + symbol.
Not sure the significance but to me these seem like choices rather than errors, perhaps to fit some other information hidden here in the untransposed cipher or plaintext.
Congratulations to Dave,Sam and Jarl! Amazing work! Been fiddeling with the Zodiac webtoy, Zkdecrypto and lurking these forums WAY too many hours during the years since the Zodiac movie came out, 07 was it? Will was strong, but mind weak. 
What a relief, now i can sleep!
If the sob is still out there and not in hell may be he will respond with a fresh letter…
was there anything significant about the crossed-out letter? What did it turn out to be?
Good question!
It turned out being the 15th letter which is the "i" in "having". The early part – "I hope you are having"
Looks like zodiac had a normal forwards "k" (which is "A" in the key) there before his correction – which he then changed to the backwards "k" which is the letter "i" in the key.
If the sob is still out there and not in hell may be he will respond with a fresh letter…
He’s in all the papers again, must be delighted if he’s still alive. Or uneasy.
was there anything significant about the crossed-out letter? What did it turn out to be?
Good question!
It turned out being the 15th letter which is the "i" in "having". The early part – "I hope you are having"
Looks like zodiac had a normal forwards "k" (which is "A" in the key) there before his correction – which he then changed to the backwards "k" which is the letter "i" in the key.
Thank you! A simple goof…but I can see why he wouldn’t want to mess with a do-over.
“…they may be dealing with one or more ersatz Zodiacs–other psychotics eager to get into the act, or perhaps even other murderers eager to lay their crimes at the real Zodiac’s doorstep.“ L.A. Times, 1969
INCREDIBLE WORK! I am so thrilled to read about the solve!!
I have one question … looking at the undeciphered version … there was a lot of talk at one time thinking that it should/could be solved by somehow looking at it in 4"quadrants" so to speak. Each "quadrant" having the word "BY" in plaintext. And it also looked like one should possibly fold the cipher in half given the hyphens at the ends of the lines in almost the middle of the page. Did this turn out to be of any use when working on the solve? Did either of those things play into it? Do all the "B"’s and "Y"’s decode to the same letters? If so – what letters?
Is there possibly a second ‘solve’ that can be done using the 4 quadrant ‘theory’ as it were?
Amazing find, congrats to the team. I’m not sure if it was explained in the video how you managed to get the first hit on ‘gas chamber’ etc.. Were you manually inputting those 600K transpositions and looking at the results (yikes!), or was the computer doing that to some extent? Also, I think it was mentioned that ZK Decrypto is able to mostly solve it right away once the proper order was obtained, but you had to manually ‘crib’ those words in. Do I have that right, and if so, why didn’t your program figure it out right off?
Excuse my ignorance, not a cipher guy. But damn amazed at all this.
Amazing find, congrats to the team. I’m not sure if it was explained in the video how you managed to get the first hit on ‘gas chamber’ etc.. Were you manually inputting those 600K transpositions and looking at the results (yikes!), or was the computer doing that to some extent? Also, I think it was mentioned that ZK Decrypto is able to mostly solve it right away once the proper order was obtained, but you had to manually ‘crib’ those words in. Do I have that right, and if so, why didn’t your program figure it out right off?
Excuse my ignorance, not a cipher guy. But damn amazed at all this.
Jarlve’s AZdecrypt codebreaking software has a "batch" mode, where you can stuff all the ciphers into a single file. Then you just tell the software to go through all the ciphers in the file and try to solve them. The first results AZdecrypt found for the transposition that was correct for the first 2 sections was:
EHOPE YOU ARE HE SING IST TORRA ENN TRYING
TO CATCH METH AFTAINT MT ON THE TS SHOT WHICH
BRINGS UP ALS IN TABS IT ME NAME OF AR HEED
OR THE GAS CHAMBER BECA ATE IT WILD VENT
ME ROLER A DICE AI I THE VS SHEN BECAUSE
TOO WHA SEEN TIGHT DESERTS WORS ROS ME THERE
EVERYONEED HE HAS NOTHING THEN THEY HE ACH
PARADICT IS THEY ALREARE AND NORDER THER
AMEO EARRE AND BECAUITE IS YOT TV HAT MR
NEWE ITLE NEVER IND BAEYN NEIA AT A HOE CDR
PET
Phrases I found interesting at the time are in boldface.
I didn’t get a clean solve until I isolated the first 9 lines, locked in "gas chamber", "hope you are", and "trying to catch me", and then asked AZdecrypt to do a search for the key that produces the best-scoring plaintext. And then the correct one was found!
