write up ctf by ariafatah

ariaf.my.id/ctf_aria/cryptography/M_substitution1.html


soal

A second message has come in the mail, and it seems almost identical to the first one.
Maybe the same thing will work again.
Download the message here.

hint

  • Try a frequency attack
  • Do the punctuation and the individual words help you make any substitutions?

solve

wget https://artifacts.picoctf.net/c/181/message.txt

cat message.txt
# ZWDg (gejfw djf zacwpfx wex dqar) afx a wscx jd zjicpwxf gxzpfbws zjicxwbwbjv. Zjvwxgwavwg afx cfxgxvwxm hbwe a gxw jd zeaqqxvrxg hebze wxgw wexbf zfxawbybws, wxzevbzaq (avm rjjrqbvr) gnbqqg, avm cfjtqxi-gjqybvr atbqbws. Zeaqqxvrxg pgpaqqs zjyxf a vpitxf jd zawxrjfbxg, avm hexv gjqyxm, xaze sbxqmg a gwfbvr (zaqqxm a dqar) hebze bg gptibwwxm wj av jvqbvx gzjfbvr gxfybzx. ZWDg afx a rfxaw has wj qxafv a hbmx affas jd zjicpwxf gxzpfbws gnbqqg bv a gadx, qxraq xvybfjvixvw, avm afx ejgwxm avm cqasxm ts iavs gxzpfbws rfjpcg afjpvm wex hjfqm djf dpv avm cfazwbzx. Djf webg cfjtqxi, wex dqar bg: cbzjZWD{DF3LP3VZS_4774ZN5_4F3_Z001_4871X6DT}

tool

  • https://www.quipqiup.com/ alt text
    picoCTF{FR3QU3NCY_4774CK5_4R3_C001_4871E6FB}
    

manual

# ...

flag

picoCTF{FR3QU3NCY_4774CK5_4R3_C001_4871E6FB}