I would be a terrible FBI cryptanalyst.
My solve rate is shit.

Oh I don’t think you’ve done too bad. I don’t see anyone complaining fella.

Wow, just wow. I truly believed it couldn’t be solved due to some convoluted path used and the message length being too short. Had to walk away from trying to solve it 5 years ago because it was consuming way too much of my time. Thought about it so many times since then, but was too afraid to dive back in. Turns out both of the observations I discovered (I probably wasn’t the first one to find them though) were significant: viewtopic.php?f=81&t=2625
I just couldn’t imagine the weird-ass 9 + 9 + 2 lines split. So in the end, the encoding path wasn’t all that convoluted, just, well, illogical.

Looking at the initial partial solve in the YouTube video, that lead to the correct solution — I would’ve missed it too. Just too many nonsense sequences, I would’ve chucked it. Definitely congrats on being so observant. And persistent. So many years, and it’s finally solved. I have to say, this thing has been bugging me for such a long time, I’m glad I can finally let it go for good. Thank you just for that!

I just realized I forgot to credit you for the period 19 discovery. I think you and Jarlve discovered the same phenomenon independently. I’ll mention it in the next video. If you want me to use your real name, PM it to me (or just post it here). Otherwise I’ll use your forum name. The period 19 repeating bigrams discovery really started a whole chain of events that led to this great success, so thank you very much!!

I would be a terrible FBI cryptanalyst.
My solve rate is shit.

Not sure what else you’ve worked on or just how low your batting average may be – but you guys hit a grand slam in the 7th game of a world series with this z340 solve. The z340 had to of been the most infamous un-cracked cipher going into last week.

I just realized I forgot to credit you for the period 19 discovery. I think you and Jarlve discovered the same phenomenon independently. I’ll mention it in the next video. If you want me to use your real name, PM it to me (or just post it here). Otherwise I’ll use your forum name. The period 19 repeating bigrams discovery really started a whole chain of events that led to this great success, so thank you very much!!

Dave, you had it solved 2 years ago, but I guess Zodiacs chosen wording was keeping you from getting over last hurdle to a key.
More Bigrams!

YouTube link to presentation below. Period 19 starts at about 19 minutes in video. Static picture capture from Youtube Video below Youtube video.

https://www.youtube.com/watch?v=3Hk__Hk5c9M&t=653s

[attachment=0]IMG_0108-3.jpeg[/attachment}

https://www.youtube.com/watch?v=3Hk__Hk5c9M

I just realized I forgot to credit you for the period 19 discovery. I think you and Jarlve discovered the same phenomenon independently. I’ll mention it in the next video. If you want me to use your real name, PM it to me (or just post it here). Otherwise I’ll use your forum name. The period 19 repeating bigrams discovery really started a whole chain of events that led to this great success, so thank you very much!!

Dave, you had it solved 2 years ago, but I guess Zodiacs chosen wording was keeping you from getting over last hurdle to a key.
More Bigrams!

YouTube link to presentation below. Period 19 starts at about 19 minutes in video. Static picture capture from Youtube Video below Youtube video.

https://www.youtube.com/watch?v=3Hk__Hk5c9M&t=653s

[attachment=0]IMG_0108-3.jpeg[/attachment}

https://www.youtube.com/watch?v=3Hk__Hk5c9M

Definitely on the right track but I believe the period 19 was throughout the entire cipher at that point starting with the 1st symbol.

The issue preventing a solve was the fact Z split it up into 3 sections.

Starting the period 19 with the 1st symbol but only for the first 9 lines.

Then starting again with the 1st symbol of the 10th line.

Then not using the period 19 for the last two lines choosing to reverse some of the words instead.

Tricky little demented bastard.

EDIT: I wonder if he decided to do this on the fly. Maybe he noticed that when he started the first string of the period 19 with the 1st symbol of the 1st line he liked how it landed neatly on the last symbol the first 17 by 9 section.

Maybe because of that he thought to start again with the 1st symbol of the 10th line and end neatly once again on the last symbol of the 2nd 17 by 9 section.

At this point, maybe with only two lines remaining he changed to simply reversing the some of the words.

I just realized I forgot to credit you for the period 19 discovery. I think you and Jarlve discovered the same phenomenon independently. I’ll mention it in the next video. If you want me to use your real name, PM it to me (or just post it here). Otherwise I’ll use your forum name. The period 19 repeating bigrams discovery really started a whole chain of events that led to this great success, so thank you very much!!

Dave, you had it solved 2 years ago, but I guess Zodiacs chosen wording was keeping you from getting over last hurdle to a key.
More Bigrams!

YouTube link to presentation below. Period 19 starts at about 19 minutes in video. Static picture capture from Youtube Video below Youtube video.

https://www.youtube.com/watch?v=3Hk__Hk5c9M&t=653s

[attachment=0]IMG_0108-3.jpeg[/attachment}

https://www.youtube.com/watch?v=3Hk__Hk5c9M

Definitely on the right track but I believe the period 19 was throughout the entire cipher at that point starting with the 1st symbol.

The issue preventing a solve was the fact Z split it up into 3 sections.

Starting the period 19 with the 1st symbol but only for the first 9 lines.

Then starting again with the 1st symbol of the 10th line.

Then not using the period 19 for the last two lines choosing to reverse some of the words instead.

Tricky little demented bastard.

EDIT: I wonder if he decided to do this on the fly. Maybe he noticed that when he started the first string of the period 19 with the 1st symbol of the 1st line he liked how it landed neatly on the last symbol the first 17 by 9 section.

Maybe because of that he thought to start again with the 1st symbol of the 10th line and end neatly once again on the last symbol of the 2nd 17 by 9 section.

At this point, maybe with only two lines remaining he changed to simply reversing the some of the words.

This will be debated for years on how he did it.

I’m sure it’s been pointed out since, but the Z408 was also divided into 3 sections – even more obviously. I wonder if this type of three-part division is common in codemaking or if this is something peculiar to Zodiac?

It,s really not that hard.

1. come up with your plaintext, 340 characters.

2 divide it up in three chunks, 2 of them 153 characters long, 1 34 characters

3. take 1 gridded paper,17 columns, 9 rows.

4. fill in your plaintext in the columns, top to bottom, downwards the nine rows, starting in the upper left corner and then countinue left for all 17 columns (9×17=153)

5. Take another identical gridded paper, draw a "staircase" from upper left corner, under row 1, make it 2 columns long, then one row down, all the way down.

6. Just move over your text from the first paper, but read and copy it in horizontal, from left to right. the top row should look just like it does on your first paper.

7. here’s the trick, on the following lines, when you copy over your previously written horizontal rows of text (which should look like jibberish), start at the "staircase"
i:e two columns to the right compared to row one,

8. fill in your text that you have on your 2nd row on the first paper, when you filled the row, you’ll have to take your last two letters and place them in the empty space
in front of the "staircase" on the same row.

9. repeat for all the rows, starting at the staircase you drew. for every row there’s two more letters that has to be moved from the end of the line to in front of the staircase.
(0 for row 1, 2 for row 2, 4 for row 3 and so on.)

Now you filled out the first part, 153 letters and it only took like 15 minutes.

Do the second and third part, then of course you have to encipher the whole thing with the 340 key. make a mess of the 2nd and 3rd part, while you’re at it!

Then wait 51 christmasses for reply.

https://imgur.com/a/TiphxRW

This is just me sitting at home and passing time since i got a mild case of the corona virus, In no way do I mean to be disrespectful by making light of the serious and tragic subject matter, it just so happened that my plaintext in my experiment turned out to be a letter to Santa inspired by the actual ciphertext. I really just wanted to see if i could figure out some method the 340 came to be. Im sure it’s possible to do in a more, and even less sophisticated way. (My initial method was to write 19 columns, 9 rows of plaintext (figuring a lot of gridded papers are typicaly 19-20 columns) and then write that over to 17 columns and that way achieve the "move two over" , but that did only work out partially…maybe i,m thick. Sorry also, if theres any mistakes!

My appoligies if I accidentaly offended someone, in hindsight maybe this is not the place for "humorous" stuff. Peace! /Hoek

Hello doranchak do you think that z May have not really known how hard this was cipher was going to be to crack or maybe that law-enforcement did receive other keys to it considering he had kind of talked about current topics The TV show and what was talked about on the TV show with the gas chamber ? Thank you

People solved extremely hard codes during WWII, such as Enigma, so I can imagine Z would have thought "well if they can crack something like that, surely they can crack something like this!"
The difference may have been that his code didn’t get attacked using anywhere near the same amount of resources that were devoted to breaking WWII era codes.
Perhaps if Zodiac had invaded Poland, the code would have been defeated sooner…

Enigma! Love it.
Correct me if I’m wrong (also, I’m no expert whatsoever) but theoretically Enigma was much easier to break, because the Allies knew its general working and layout. That is, they didn’t have to guess a transposition as you did.
Also, Enigma had a weak point, that no letter could be encoded as itself (though I can’t remember what was the practical advantage for the Allies about that). (Edit: I think the whole process started with narrowing down the solutions by eliminating each letter as encoded by itself).
Human mistakes and laziness helped a lot as well: messages sent with the positions of the previous day, unimaginative starting positions, and the ubiquitous tag at the start of daily meteo transmissions.
The real challenge for Enigma decoders was to find positions and keys, everyday, in a short time, with limited computational resources.
I guess Zodiac should have known how hard his code was to break, e.g. compared to Enigma. You had to find out the rules, that was the hardest part.

HIndsight…

Looking at this now, it see a diagonal cluster. Coincidence?? Asking genuinely.

At the time I did this…I certainly didn’t notice. viewtopic.php?f=81&t=856

My appoligies if I accidentaly offended someone

I don’t think you have (or will).

Then wait 51 christmasses for reply.

HIndsight…

Looking at this now, it see a diagonal cluster. Coincidence?? Asking genuinely.

At the time I did this…I certainly didn’t notice. viewtopic.php?f=81&t=856

I was trawling through old posts/threads (2013) regarding this so just gonna add the links for those. Just for reference as part of this journey and those are the two threads where you posted the above message T.

viewtopic.php?f=81&t=856
viewtopic.php?f=81&t=964

Fantastic work!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Kudos for the amazing work!!!