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I'm needing some help deciphering the following puzzle:

Oi xmt gcilk vwf-cciruk Lhoyqz ccig spkb mfyt; Rnbrl uakoj tbbu gw bkgd, Wgqnb ddmu p zfoim; Viec kfs lllsmt, ywfy dg zdoc, Dtfl fu xggu, Ii qjr tstfz wjd-cwtovb Pdgm lgf.

Xrb Ifg, lfhtei lbiwfr lmvp Hdo Tfz rdahp nuyqbdw, Mtfrid aic ngzok xxhyl kinr ncde Ipbn Mm effrw im dbilp: Oi xmt gcilk vwf-cciruk H ntgzmr-gsdtf zgfkweru Oku Cghd Lxf Gdvakxai Jrdry Smobua.

Bnfshm rfo Llw, uhfo Emvbiglw Uobdjdg iakxa lnj cbn, N houpzffai ak fdpp Pop a vytlvbhoc gq hgj; Nieajl vgh Hdo, xmev Drwiys Kyms ufyr qiqobm, Umv fz fgk lsy ytj sgquc Eviut bjebt.

Fgmbly ytj Nbnlposesd Pgp mdyf mltmmiru okuki, Ahrvrhcv drs zbrgajdf Okamosej qjr ndo; Gja knsj Jdj Vbixih Ii tnb fgahfo mlddv Cebwllxcej qjr Trpdrip Wdqj g bdwx.

Iplt uyt D idxu Xfz, Pfxi gj D ds? Ll J wrvn g Jmtvxihd D gaadj falos a syph; Ck A zfdb a Cwvr Fgu B igglj ca vp wdah, Tbt ctbo C udr L mjvr Tov, Idxu et vegvu.

We were also given three clues:

  • Hint 1: SO, YOU LIKE TO PLAY CASTLEVANIA?
  • Hint 2: Thomas Shelby
  • Hint 3: Balaur.
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    $\begingroup$ Hi, and welcome to Puzzling.SE! Could you provide a source for this puzzle, please? $\endgroup$
    – Brandon_J
    Feb 7, 2019 at 20:19
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    $\begingroup$ Sure! This is actually for a dungeons and dragons campaign I'm in. Our game master gave us this riddle with the prize being an inspiration point for solving it. $\endgroup$ Feb 8, 2019 at 0:05

2 Answers 2

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Plaintext

In the bleak mid-winter Frosty wind made moan; Earth stood hard as iron, Water like a stone; Snow had fallen, snow on snow, Snow on snow, In the bleak mid-winter Long ago.
Our God, heaven cannot hold Him Nor earth sustain, Heaven and earth shall flee away When He comes to reign: In the bleak mid-winter A stable-place sufficed The Lord God Almighty Jesus Christ.
Enough for Him, whom Cherubim Worship night and day, A breastful of milk And a mangerful of hay; Enough for Him, whom Angels Fall down before, The ox and ass and camel Which adore.
Angels and Archangels May have gathered there, Cherubim and seraphim Thronged the air; But only His Mother In her maiden bliss Worshipped the Beloved With a kiss.
What can I give Him, Poor as I am? If I were a Shepherd I would bring a lamb; If I were a Wise Man I would do my part, Yet what I can I give Him, Give my heart.
In the Bleak Mid-Winter by Christina Rossetti

Cipher

Quagmire 3 with a mixed alphabet derived from the keyword CENTURION and a repeating key of EUSUNTDRACUL

Solve path

Identify the cipher as polyalphabetic by finding that the letter frequency is visibly flat, or that its Index of Coincidence is 4.1% which is very close to the "random" value of 3.8%. Identify the cipher as a periodic cipher using either the Kasiski test or the Index of Coincidence.

The Kasiski test searches the text for long repetitions and finds common factors among the distances between them. The long repetition Oi xmt gcilk vwf-cciruk (216) and the short ones ej qjr (48) and ruoku (204) together suggest a common factor of 12.

The Index of Coincidence can be used to detect the period, but it generally isn't done by hand because of the amount of computing and tabulation required. There are two different ways to apply it. Briefly, the Kappa IoC counts the distances between repetitions of individual letters, and finds the most frequent distances. The Kullback test writes the text in rows of width N, reads down the N columns, and takes the average of the plain IoC of each column. The test is repeated for various values of N and the highest result indicates the period. Both tests indicated a period of 12.

If it is a periodic polyalphabetic cipher, then there are 12 simple substitutions (alphabets) used in order, repeating throughout the cipher. Since the cipher is given with word spaces, punctuation, and capitalization intact, I opted to write a number above each letter in the cipher to indicate which alphabet it uses:

12 345 6789a bc1 234567 89abc1 2345 6789 abc1  23456 789ab c123 45 6789
Oi xmt gcilk vwf-cciruk Lhoyqz ccig spkb mfyt; Rnbrl uakoj tbbu gw bkgd,
.. ... ..... ...-...... ...... .... .... ....; ..... ..... .... .. ....,

I began by assuming that any single-letter capitalized word that didn't follow a period was the word I, and any single-letter lowercase word was a.

  abcdefghijklmnopqrstuvwxyz
1 ..........................
2 G.........................
3 ........C.................
4 ........D.................
5 ........A.................
6 ..........................
7 P.........................
8 ........H.................
9 ..........................
a ..........................
b ........D.................
c ..........................

 [...] abc1 23 4 56  78 9 abc1 2 3456789a b c1234 [...]
 [...] Pfxi gj D ds? Ll J wrvn g Jmtvxihd D gaadj [...]
 [...] .... a. i ..? .. . .... a ........ i ..... [...]

After a few choice assumptions of words like the and in, I noticed that three of the alphabets were identical to each other, and that the alphabet labeled "a" was the identity alphabet, which didn't change any letters. The identity alphabet also established that this was a Quagmire 3 system. I continued assuming words until my enciphering grid was full enough to chain out the alphabet and discover its keyword. With the alphabet recovered, all I had to do was read down the "C" column of the grid to find the repeating key, since "C" is the first letter of this alphabet.

To read more about solving a Quagmire 3, I recommend Solving Cipher Problems by Frank L. Lewis.

Other solve paths?

The hints don't seem to be much help with actually solving the cipher.

The hint about Castlevania seems like it would clue the cipher's repeating-key EU SUNT DRACUL, but the phrase used as a key would only be known if you had played and completed the 2010 game, and then watched the post-credits scene - or just watched it on Youtube, for whatever reason. Even so, guessing this key (and in fact, guessing the Quagmire 3 system too!) correctly doesn't help you very much when the Quagmire alphabet (CENTURION) is unknown... you don't even know which letter is the "index" letter under which the key letters are aligned.

The hint "Thomas Shelby" is the name of one of several Peaky Blinders characters who use a phrase from this poem ("in the bleak mid-winter") as a sort of catch-phrase. Anyone who is already familiar with the poem (or even just the line from the show) would recognize it by the pattern of word spaces and lengths and punctuation. Let's hope the dungeon master doesn't ask you for the cipher keywords, if you just tell him the poem.

I can't find any connection between the hint "Balaur" and the solution.

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  • $\begingroup$ The Balaur is a mythological creature. $\endgroup$ Jun 26, 2023 at 6:40
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Alright, here's a starting point:

The CAPS LOCK Castlevania hint indicates that we can likely find some of the following special words: Belmont, Vampire, Dracula, monster, etc. This could come in handy later. As for the other hints, The Balaur is a mythological creature similar to a dragon; Thomas Shelby is a family crime boss in a TV show. Not sure how that last one will fit.

Digging in:

if this isn't a monoalphabetic (see wikipedia for definition) cipher, then I'll likely be no help. I'll be looking strictly at monoalphabetic possibilities.

An interesting word:

cciruk. The necessary word pattern for this word is fairly limited. Our only possibilities are aahing eerily llanos oocyst oocyte oodles oogamy oogeny oohing oolite oolith oomiac oomiak oompah oomphs oorali ootids oozier oozily oozing "c" is likely a vowel of some sort, since llanos is a Spanish word.

This doesn't jive well with any other possibilities.

Something else discouraging is the "Mm" and the "Ii" - unless the author of the puzzle is deliberately throwing in fake words, this is probably polyalphabetic, in which case I can't help.

I'll see if I can find anything else.

Some possible clues:

Sypha, in the Castlevania series, took the pseudonym Cipher.

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  • $\begingroup$ Another thing the three clues have in common is rot13(Ebznavn). Tried this as a key, along with some of the words in part of your answer but no luck yet. $\endgroup$ Feb 7, 2019 at 21:13

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