i've been messing around with classical cryptography and ended up making a two-page puzzle called nachtlorn.

i initially made it for some friends, then tried throwing it at a few AI models, including local qwen models. none of them managed to recover the intended answer. some picked up on interesting patterns, though whether those actually led anywhere is another question.

i'm curious how people here would approach it, and whether the construction holds up to someone who actually knows their cryptanalysis.

a few things worth mentioning:

• it's a reversible cipher, not a hash.
• underlying plaintext is in english.
• there's a definite answer, although i'd consider an explanation of how you recovered it more important than simply guessing the right word.
• formatting is intentional.

i'm deliberately leaving out the mechanism for now. if people get stuck, i'll add progressively more revealing hints in spoilertext, so anyone who wants to attempt it blind still can.

i'd also appreciate criticism of the design itself. particularly whether it's genuinely difficult, unnecessarily convoluted, or simply missing information a solver would reasonably need.

i also have an exact TXT transcription, including the original spacing and indentation, if anyone wants to work with the ciphertext programmatically. just ask and i'll drop it in the comments.

code, external references, and collaborative attempts are all welcome.

please spoilertext any potential solutions.

Jack.B

Part of a trail — built to be solved, not to stump you. The reward is a scene.

The first sign was between the places. The second was the shape of an absence. The third is a weight.

Keyed Vigenère. The key is a single word: the word the second sign ends on. (Those who solved the second already hold it.)

TIWHB YWESC RRNXW IWVRV LEGDS BTAAT OLBNI AOVJR NXTIW THNPO GSVBQ QTISX JCWNP LXUGV EOGGE CGKOG LBNPO XKSHP HOODC UKWHB FHFJI AWAIE QZESF SGJMN HLLRV LISVW VIRIT SARKK HULLR GCEDS RAQXF JFH

158 letters. Standard tabula recta. English plaintext.

Previous sign → [INCOLLA QUI IL LINK DEL TUO POST N.2 SU r/ciphers]

Here is the cipher typed out:

VSWIW PGT HVS DCT WYLUGCW JBWZ IWPI OVSK HMTHTQFYJ AWZY

IH EGZPMKE ATS WNENA CB GIHXUSM HPGPW IHWY BWTL NF NBUN

VJAVWBZLZ VD GDRZ GPMQFMRK OH WRPQC CLYF MFBZMUMTG AYHNFS

135 125

For context, this is a favicon for my website, from far off it looks like a B and kind of like a D. Inside the image is a hidden message, and i want to see if anyone can actually figure it out, its very easy.

5670646F6F20756C73736F68207772207A647570207873206272787520697272672028776B7568682920474554204F4E204D592057415645204C454E475448
(the answer, requires some research but will become a number)

[Challenge] Can you crack this keyed 6×6 Polybius cipher?

I've encrypted a short English sentence using a keyed 6×6 Polybius square. Can you recover the original plaintext without any hints?

Ciphertext

q 9fo zrhv tx8

How it works

The square contains all 26 English letters (A–Z) and the 10 digits (0–9).

1. I constructed a keyed 6×6 square using a secret keyword. The keyword determines the arrangement of the symbols.
2. I encrypted each plaintext character by finding its row and column in the keyed square.
3. Instead of keeping the coordinates as coordinate pairs, I mapped each pair back to the character occupying the same position in the standard square.
4. I preserved the original spaces.

The standard square uses the symbols in sequential order, filled row by row:

A B C D E F
G H I J K L
M N O P Q R
S T U V W X
Y Z 0 1 2 3
4 5 6 7 8 9

There is no transposition step involved.

Your challenge

• Recover the original English sentence.
• If possible, explain how you derived it.

I'm interested in how far you can get using cryptanalysis alone, without hints from me.

Good luck!

P.D.: this should be unsolvable, if it wasn't for the spaces, idk

The first sign was between the places. The second isn't a line — it's a small story. Solve it and you get a moment, not a motto.

Keyed Vigenère. The key is a single word: what the bell leaves behind.

SBOYF MXZMM IYNVS VRSAE ISVOW GQTHM OXBQW GWYSA VLWZZ SSUXZ MMSLJ ISZOX UGWAT PRPGM LTPJG VLWAP GBPHK QRRJC WFWEX UGWGC YHOWX LPPWU CTWWQ MGUET APRPG

125 letters. Standard tabula recta. The third sign follows this one.

First sign → https://www.reddit.com/r/codes/s/3KpkjcXo8N

The Sator Square doesn't change when you transpose it — I think it's a working cipher. Verifiable demo inside

I reverse-engineered a mechanism out of the Sator Square's structure, and I want people to stress-test it.

The square (SATOR / AREPO / TENET / OPERA / ROTAS) is invariant under transposition: swap its rows and columns and you get the identical square. My claim: the square embodies that operation, and the operation is a transposition cipher.

- Encrypt: write a 25-letter text across the rows of a 5×5 grid, read the ciphertext out down the columns.

- Decrypt: write the ciphertext down the columns, read the plaintext across the rows.

Demonstration — the opening of Genesis 1:3 in the Latin Vulgate, first 25 letters, spaces removed:

DIXITQUEDEUSFIATLUXETFACT

Written across the rows, read down the columns, the ciphertext is:

DQUTTIUSLFXEFUAIDIXCTEAET

Run it backward and the verse comes back letter-for-letter. No substitutions, nothing added, nothing left over. You can verify the whole thing by hand in two minutes — please do.

Full write-up with the grids and an interactive version you can run yourself:

https://muse.ai/s/the-jessim-theory-xnxm6xnxyxapinth/uRqAXorK715J9-J90a-OJOY62xngl91oMNn8zVjv_mQ

What I'm claiming: the mechanism is real and reproducible. What I'm not claiming: that this proves anyone in antiquity actually used it — that would need historical evidence I don't have.

Two questions for this sub:

1. Has anyone seen this specific formulation before — the square as the fixed point of the transpose, used as a cipher for outside texts? I know the Pater Noster anagram literature; this is a different operation.

2. Where does the mechanism break? Edge cases, longer texts, chaining grids — push on it.

The claim statement and paper were timestamped (OpenTimestamps, Bitcoin-anchored) on October 27, 2026, before posting this.

— Jessica J. Trofholz