Toy cipher I made for a reddit challenge

From	Leo <usenet@gkbrk.com>
Newsgroups	sci.crypt
Subject	Toy cipher I made for a reddit challenge
Date	2021-09-27 21:15 +0000
Organization	A noiseless patient Spider
Message-ID	<sitca4$518$1@dont-email.me> (permalink)

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Hi sci.crypt,

Around 4 months ago, I posted a small challenge [1] to /r/codes. I
removed functionality from the cipher in successive steps in order to
make it easier to crack the full thing, but no one there seemed to
progress further than the first level.

[1]: https://old.reddit.com/r/codes/comments/nk0mcv/
cipher_challenge_with_multiple_levels/

So I figured I'd post some ciphertext here in case anyone finds it a
fun challenge. Normally the cipher supports a key and prepends a nonce
to messages, but I've left those empty in this post to make this
easier to approach.

Here is the ciphertext:

QVMEJ RZKGX BCQTQ LSJLZ MNBJV IKFER ZERNS OTCCT KSJSX GLEER 
NUPDB GVTDG PPAQG VLCAE ITZDB IVZUQ MIPYP CNUTC HRDTJ CIAYQ 
PRDNI BKGVG HNASG YTQIJ VHOGF EHOXA JHDHU HPSNW FCAJU PMHKM 
WDLHQ YQSFD CMAEB DLDQQ HAMKO KACRD DEVFD HELAC PXBJL JLPIB 
HPKQE BHFBS JHHPN BXOOY LUYFR RZURG SZZZG XIBYA RCWKD AGUYX 
VDRNB LBGAJ DPWDE IBPQM HMYTX KZCAY AVWHT TOVNB DKKTG NPIVL 
XQDXR FZVSH XJUZA NCJKC XDDEH YGXSJ GORGO WNTEA ZHGAO MVXUA 
YZUTW CKNBF PXCNB UYTUT YBTAG YEQWP HEFSC XCCXQ KSTIY SEJZE 
PPEFQ HLJKP VUDMP KTYBH BSUTT EPKIO BMGRU CSBFU AAWBM WWSDT 
IHBSX FYUTL UPMAR LXBSM SGXWS FQNGW XLIHR KZJMI NFFPC YNDWH 
GNQNE UYQXP JDYUU XNDGY UOELV CJJQG CRJYE VZMQR CECPT RJGRH 
FSZGH UIFYG CZBDW SJWTX GATCE ITGAL AURHE VOCSE NWVKC UYZYW 
BWRHV CZHKB CIURC YJTGI YVHVY FNWEV RKHBE SHMXN GDEXV IZJQV 
QKYNB NPSON SRTXP FWQTP ECAUR BYHAT UYDBS LRQHD DMQEH RTDJA 
RWFNQ DEEBZ CQJDS FHYMJ RFNLO KDNDJ GNCCB DGATV WIHZL DLMWX 
SGEGF FWEZL WQSJO PKYIL JVGGQ BBSCS QSMFS IDYTM QEHYY ULUSM 
JWNKP KGSPN HUFIR OZMDB AVMEH UXQCN CYHQL ZOJET LAGFL HXDFD 
JPSSY ZECAS QAYEM SNZGE RNIBD WQWHY VNXNN BIZIX UANLB SWEIT 
PEGCR IGQCK WMMDQ SQZPD AZFDS ELPCD XYWXZ LH

And the plaintext for it:

> Quentin Coldwater is a high school student from Brooklyn who along
> with best friends James and Julia attends an advanced school He
> loves a series of books called Fillory and Further which involve the
> children of the Chatwin family discovering a Narniaesque magical
> land called Fillory On the day of his Princeton interview Quentin is
> instead transported to Brakebills College for Magical Pedagogy the
> only school for magic in North America He passes the tests and
> interviews is accepted as one of twenty new students After beginning
> his studies at Brakebills it becomes apparent that magic is
> difficult and tedious to learn The curriculum involves learning many
> old and lost languages and innumerable hand positions Despite this
> Quentin and his classmates Penny and Alice are allowed to move up a
> year by compressing their first year of studies Penny fails the
> special exam and stays behind then later fistfights Quentin out of
> jealousy One day during class a bored Quentin tampers with a spell
> An otherworldly horror referred to as the Beast enters Brakebills
> eating a student before the faculty are able to drive it away

As for the challenge, try decoding the following ciphertext, encrypted
in exactly the same way.

IDPIP INPZN EGLQZ JSQLX MVLFE RSBJV ZIOJJ MDPCD JQQRF VYZYV 
UAIAU XDHFT WXDWJ HYFOD OIVZZ VMORF SOXPA GOPUW MURKC EMKYR 
YPPCE IIIGL KUODI HZJCV DPRWU LMJDS NNPOR IRKKU AMWPR HQJNB 
WPWSE UEWAR LEDHD XOGOV RSOLE XQNSF BKUHI AKVAR JLLVX RKQOS 
EPSPR RVEZK KJHOM ATCDH GDGNA MCSRW IOAQO LCMOZ XWEOG EHVCQ 
QVOZC SELQD LXMXK UFNOT RGOOE QQWIF USQFN CCYNY QULVA VNUFR 
YQKOD DLCVH LWYB

-- 
Leo

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Thread

Toy cipher I made for a reddit challenge Leo <usenet@gkbrk.com> - 2021-09-27 21:15 +0000
  Re: Toy cipher I made for a reddit challenge Richard Heathfield <rjh@cpax.org.uk> - 2021-09-27 23:12 +0100
    Re: Toy cipher I made for a reddit challenge Leo <usenet@gkbrk.com> - 2021-09-27 22:32 +0000
    Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-09-28 00:51 +0200
      Re: Toy cipher I made for a reddit challenge Leo <usenet@gkbrk.com> - 2021-09-28 04:04 -0500
        Re: Toy cipher I made for a reddit challenge Richard Heathfield <rjh@cpax.org.uk> - 2021-09-28 11:29 +0100
        Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-09-28 21:11 +0200
          Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-09-29 00:00 +0200
            Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-09-30 23:07 +0200
              Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-01 22:29 +0200
                Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-10-02 04:20 +0200
                Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-10-02 12:18 +0200
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-02 13:28 +0200
                Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-10-02 16:25 +0200
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-02 17:25 +0200
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-02 12:28 +0200
                Re: Toy cipher I made for a reddit challenge Leo <usenet@gkbrk.com> - 2021-10-02 10:42 -0500
                Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-10-02 18:13 +0200
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-03 12:27 +0200
                Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-10-03 18:02 +0200
                Re: Toy cipher I made for a reddit challenge Stefan Claas <spam.trap.usenet@gmail.com> - 2021-10-03 09:23 -0700
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-03 21:32 +0200
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-18 08:52 +0200
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-18 19:24 +0200
                Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-10-19 00:47 +0200
            Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-17 17:17 +0200
              Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-10-17 20:05 +0200
                Re: Toy cipher I made for a reddit challenge Leo <usenet@gkbrk.com> - 2021-10-25 17:18 -0500
                Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-10-26 20:03 +0200
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-27 19:49 +0200
                Re: Toy cipher I made for a reddit challenge Leo <usenet@gkbrk.com> - 2021-10-27 17:15 -0500
                Re: Toy cipher I made for a reddit challenge Max <maxturv26@gmx.net> - 2021-10-28 12:51 +0200
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-28 13:33 +0200
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-10-31 22:17 +0100
                Re: Toy cipher I made for a reddit challenge Richard Heathfield <rjh@cpax.org.uk> - 2021-10-31 22:38 +0000
                Re: Toy cipher I made for a reddit challenge Leo <usenet@gkbrk.com> - 2021-10-31 18:42 -0500
                Re: Toy cipher I made for a reddit challenge "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-10-31 19:30 -0700
                Re: Toy cipher I made for a reddit challenge wizzofozz <oxxxxxxxxxxxs@gmail.com> - 2021-11-01 21:40 +0100

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