RACTF 2020 Crypto - 05

 

05

DPKFC LISLA KWMDW ERUKW XPDID
BRADA TRTMO LKKGN YUEIE LDEOC
VRTUM FLCVG RBSVS DTHDK WMHOG
TAECO MWEYM ITWOS SEFKF BEAWK
SAEOK SRSNZ RNEOR LTHIS DWZCO
RQSRA MYVSI RIRGE CZIDR MMVCR
HGBYE WSLSO CWMBU LGKDA DELQU
BWKLF CMWGQ RYSPA EZBDA PIRGW
SQSFA CLUMA RVERU ILKBA ATNOF
CKWWA TCKKI IUSWD EIAPK SWSGO
HCFYM SDODS MUORA TDEKU NRRSG
NETHD WPHRG AEODL LOEFH BEOWC
QWNAO BRUWW CCHOS OLUAC CXPWA
BEAWA ROHAR O

The flag is the name of the person mentioned in the message

Now, I couldnt solve this challenge while the challenge was running, because I got stuck on 04, nevertheless, here’s a quick writeup

Checking out the cipher statistics, the results turn out to be

Length:336 IC:47 MIC:60 MKA:73 DIC:23 EDI:25 LR:7 ROD:46 LDI:569 NOMOR:124
NIC:51 PHIC:47 MPIC:48 BDI:218 SDD:131 CDD:222 SSTD:60
HAS_L:Y HAS_J:N DBL:Y SERP:N HAS_#:N HAS_D:N HAS_0:N
DIV_2:Y DIV_3:Y DIV_5:N DIV_25:N DIV_4_15:Y DIV_4_30:Y PSQ:N
A_LDI:606 B_LDI:630 P_LDI:600 S_LDI:609 V_LDI:621 PTX:488 RDI:554
(used maximum period of: 15)
------------------------------
    Winner is Bifid with 42 votes out of 100

    vote distribution:
    Bifid 42
    Trisquare 31
    Seriated_pfair 17
    Cmbifid 9
    Quagmire 1

The best vote based on statistical analysis hints towards Bifid Cipher. Referencing this video, I got to know about cool tools.

We can use Cryptocrack to crack the cipher.

It solves the cipher, giving out the key ZXUTVQPKINBMSWOYLERAHGDCF and the ciphertext

donnieiproposewemeetupindoveratelevenpmnextweekfortheexchangeyoushouldbeong
uardasibelievesomeofourmessagesmaybeencryptedhoweveritookextraprecautionwit
hthismessagebysendingmybestmancampbelltoyoutoinpersontodeliverthekeyinadvan
ceiwouldliketosamplesomeofthegoodssoitwouldbeidealifyoubringafewmenofyourow
ntoensurethefedscantgetinourwayrocco

Fixing spaces,

donnie i propose we meet up in doveratelevenpm next week for the exchange 
you should be on guard as i believe some of our messages may be encrypted 
however i took extra precaution with this message by sending my best man 
campbell to you to in person to deliver the key in advance i would like to
sample some of the goods so it would be ideal if you bring a few men of 
your own to ensure the feds cant get in our way rocco

We can see campbell is being referrenced here, so the flag is

CAMPBELL