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It's not everyday you get a text from a dead friend, especially if you saw them being executed by guillotine, which is why D.S.I North Daniels was a bit sceptical when his ancient Nokia Cityman 1320 recieved a text (ding!) from Jane Stephen's number. Double-checking proved that it was the real deal, especially since it had Jane's trademark cipher applied to it:

Jane's Note

Text Copy

helpivfbghnkjdoaqriegotpsjqtmkprksyubqlnusxlcotwmrhrminmnvctvdsexouvusjwwvtlpfduocefwqfpwxgxqgnohmptkuqliwyhyrvmxvsduwrnsyziiwzazxtjafujyjvkovaxtzbbcbnwapkkcxqdboceghwyzdfadegyucpezhidjghvixrwqjefyxlsfrklytgiumrh

Unfortunately, North hadn't met Jane for 7 years, so he couldn't remember how the cipher worked. However, after a bit of a struggle, he managed it. Marvellous...

"Hang on, that's not right - it's complete nonsense!"

North read and reread the message, but it still failed to make any sense. Maybe he'd missed something. Jane's research on border communications made her doubt security, so she was very cautious about sending messages, so she tended to go one extra step. "Hmmm..."

North's eyes lit up, and after a quick bash on his laptop, he sprinted out of his room, and sprained his ankle on the 12th floor, so getting to the police station would take a little longer...

What is Jane's completely decoded message?

Hints

1. I've inserted a new tag - Geography

2. After some digging around in his office, I found this note in North's desk. It seemed as though he'd decoded the passage completely, and was trying to find some sort of message by picking words out:
Note with HintsText Copy = helpivfbghnkjdoaqriegotpsjqtmkprksyubqlnusxlcLOVINGrminmnvctvdsexouSONGSwvtlpfduocefwqfpwxgxqgnMAKINGuqliwyhyrvmxvsduwrnsyziiwzazxtjafujyjvkovaPINTScbnwapkkcxqdbocOCCUPYdfadegyucpezhidjghvixrwqjeTRIALSrklytgiumrh

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    $\begingroup$ I'm making substantial progress with this (I think) with an Excel-aided manual approach, but I regularly end up in dead ends and I'm currently trying to fathom a letter sequence that seems unworkable... Where have I gone wrong with rot13(QBVAT GEVOHAR TRG FNQ EBBG ERQF PR...)? $\endgroup$
    – Stiv
    Aug 3, 2020 at 22:21
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    $\begingroup$ The first two words are correct, so the ones before must be - well done! I agree it gets horrendous the more you decode, especially as it's "nonsense", so I'm adding a few "checkpoints" as hints. In the meantime, make sure nothing else trgf in the way of you solving it! ;-) $\endgroup$
    – Oliver
    Aug 4, 2020 at 14:23

2 Answers 2

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Complete answer

To continue on from @Phylyp's work - they were first to realise the encoding mechanism for the message:

"Every time a letter is repeated in the original plaintext, the letter is replaced by the next letter in sequence.

For example, the first time the letter 'e' is in the message, it is represented by 'e' itself. The next time 'e' appears in the plaintext, it is replaced by 'f' instead, then by 'g' for the third occurrence, and so on."
-- @Phylyp

Using a very manual approach to the decoding, assisted by some Excel formulae which allowed me to keep tabs on the current possibilities for each letter, I have now fully decoded the initial message (punctuation mine):

Help, I've been kidnapped! Go to:

PEOPLE, NOISY, PANEL, TOXIC, LOVING, REGIME, PASTA, RAVES, SONGS, WORKED, CRIB, CAPE, FLOOD, SLAM, MAKING, NIGHTS, DOING, TRIBUNE, GETS, DART, TONED, OCEAN, JUDGES, PINTS, TOKEN, MAJOR, MONKS, OCCUPY, TOYS, BOXING, SPOON, OFFICE, LIGHT, TRIALS, MODELS, FLAGS.

What next? Note that these 36 extra words at the end of the message:

separate nicely into triplets. Moreover, each group of 3 words is a valid representation of a location in the London area using what3words.com. Our triplets are:

PEOPLE.NOISY.PANEL,
TOXIC.LOVING.REGIME,
PASTA.RAVES.SONGS,
WORKED.CRIB.CAPE,
FLOOD.SLAM.MAKING,
NIGHTS.DOING.TRIBUNE,
GETS.DART.TONED,
OCEAN.JUDGES.PINTS,
TOKEN.MAJOR.MONKS,
OCCUPY.TOYS.BOXING,
SPOON.OFFICE.LIGHT,
TRIALS.MODELS.FLAGS.

On a map, they appear thus:

enter image description here

Now what? Well, note that in each case:

the precise square indicated on the map by the three-word triplet contains the name of a location or business. In message order these are:

Surepass
Turner Parade
Manor House Station
Angel Station
Rowans Tenpin Bowl
Yogahaven Richmond
Culpeper Community Garden
Highbury Garden
Urban Kings Gym
Rotherfield Primary School
Copenhagen Primary School
Hanover Primary School

So what does Jane want North Daniels to do?

Take the starting letter of each of the locations, insert the results into the original message and it reads in full:

Help, I've been kidnapped! Go to ST MARY CHURCH

Quick, North! Go, go, go!

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  • $\begingroup$ Bravo - well done for getting this far! $\endgroup$
    – Oliver
    Aug 4, 2020 at 15:55
  • $\begingroup$ Second edit - ROT13(Jbj, tbbq wbo sbe fcbggvat gur JungGuerrJbeqf yvax. Gur ybpngvbaf ner fvtavsvpnag gubhtu...) $\endgroup$
    – Oliver
    Aug 4, 2020 at 16:16
  • $\begingroup$ @Oliver Yup, just realised and got it nailed down I think! $\endgroup$
    – Stiv
    Aug 4, 2020 at 16:18
  • $\begingroup$ Well done @stiv! A well deserved tick $\endgroup$
    – Oliver
    Aug 4, 2020 at 16:24
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    $\begingroup$ @Oliver Thanks - that was tough work decoding, but a really nicely put together puzzle and it was great to see it all come together step by step. Well done yourself! :) $\endgroup$
    – Stiv
    Aug 4, 2020 at 16:28
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I can't solve the entire message, but here's a start. I'm happy for someone else to take this idea forward in their own answer.

The encoding works - at least in part - like this:

Every time a letter is repeated in the original plaintext, the letter is replaced by the next letter in sequence.

For example, the first time the letter 'e' is in the message, it is represented by 'e' itself. The next time 'e' appears in the plaintext, it is replaced by 'f' instead, then by 'g' for the third occurrence, and so on.

Using this idea, the message starts to be decoded as shown below (first line is cipher text, second line is decoded, with uppercase letters showing substitutions):

helpivfbghnkjdoaqriegotp...
helpivEbEEnkIdNaPPEDgotO...

i.e. Help, I've been kidnapped. Go to...

Unfortunately for me, I've not been able to make any more progress after that, and it doesn't help being on a mobile either!

I have a suspicion that this bit of the puzzle:

Jane's research on border communications made her doubt security, so she was very cautious about sending messages, so she tended to go one extra step.

indicates that there's some further decoding required beyond what I've outlined above. So, if this helps, please use this and have at it!

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    $\begingroup$ Great work - you're on the right track, just keep going! $\endgroup$
    – Oliver
    Jul 24, 2020 at 18:21
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    $\begingroup$ You could write a program to do the decryption for you, because the message is quite long, but it's gets less reliable the more you decrypt $\endgroup$
    – Oliver
    Jul 25, 2020 at 21:17
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    $\begingroup$ While the coding is unique the decoding is ambiguous. The first 'f' could be an 'f' or a shifted 'e'. You need to decide form context. $\endgroup$
    – Florian F
    Jul 26, 2020 at 11:31
  • $\begingroup$ Exactly my point, but put much better! $\endgroup$
    – Oliver
    Jul 30, 2020 at 11:11

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