01

No information about the cipher is provided

Plain text

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LHFKM GMRHC FLMMJ ULXFY JOUFC
FQFXF ZJOKP JOMMU LMRJT FFTBA
JYFFR JZFXG AWJCB ULXFI FFKRF
KPGKH RFWCF MTFRR LHFRI FMQFF
KFLWU JMUFC IOMMU FYCFF KWCYB
MFPQF CFHJG KHMJK FFPMJ PFWCY
BMMUF TMJQJ CVJOM GZMUF CFRRJ
TFMUG KHGAA FHLAH JGKHJ KLKPH
FMMUF TLCCF RMFPK JCTLA YMUFW
CYBMJ HCLBU YMFLT QJOAP PJMUG
RIOMM UFYXF LAAPF WGPFP LMMUF
RLTFM GTFMJ HJJKL KOLAA FLXFI
FRMJZ AOWVL HFKMI MUFRF WCFMW
JPFGR PJWOT FKMR

We have to solve the cipher. Considering the level and monoalphabetic substitution i.e each alphabet is replaced with other alphabet.

Quickly verifying my hypothesis by checking on quipquip I found the plaintext

Plain text

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AGENT ITS GREAT TO HAVE YOU HER E WEVE FOUND OUT THAT SOME EMPL OYEES OF EVIL CORP HAVE BEEN SE NDING SECRET 
MESSAGES BETWEE N EACH OTHER BUT THEYRE ENCRYP TED WERE GOING TO NEED TO DECRY PT THEM TO WORK OUT IF THERES 
SO METHING ILLEGAL GOING ON AND G ET THEM ARRESTED NORMALY THE C RYPTOGRAPHY TEAM WOULD DO THI S BUT THEYVE 
ALL DECIDED AT THE SAME TIME TO GO ON ANUAL LEAVE B EST OF LUCK AGENT B THE SECRET C ODE IS DOCUMENTS

Correcting spaces a bit, we get the text decrypted.txt

Plain text

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AGENT ITS GREAT TO HAVE YOU HERE WEVE FOUND OUT THAT SOME EMPLOYEES OF EVIL CORP HAVE BEEN SENDING 
SECRET MESSAGES BETWEEN EACH OTHER BUT THEYRE ENCRYPTED WERE GOING TO NEED TO DECRYPT THEM TO WORK 
OUT IF THERES SOMETHING ILLEGAL GOING ON AND GET THEM ARRESTED NORMALY THE CRYPTOGRAPHY TEAM WOULD 
DO THIS BUT THEYVE ALL DECIDED AT THE SAME TIME TO GO ON ANUAL LEAVE BEST OF LUCK AGENT B THE SECRET 
CODE IS DOCUMENTS

Hence the code we are looking for is DOCUMENTS

Alternatively, you may look up the video writeup by @hyperreality on puzzles 01-06, they were quite informative, given that I got stuck at 04
YouTube link