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This question is from a CTF that a company (EY Cybersecurity) did almost a year ago. The original website is no longer available.

Can you decipher me?

QWNobyBxdWUgbmluZ3VlbSBudW5jYSBpcmEgZGVzY29icmlyIHF1ZSBMeTBpdnNwZjhuTlI2ejVnT
VdoUk1pMGl2QzFyT3kwaXZxMU02ejlDdm1wVHZzd2pLbnhZdmxIVHZzd2o2ejVrS202aXY0OFZOa 3cv ==

What I've done so far:

  1. I've concatenated the strings: "QWNobyBxdWUgbmluZ3VlbSBudW5jYSBpcmEgZGVzY29icmlyIHF1ZSBMeTBpdnNwZjhuTlI2ejVnT", "VdoUk1pMGl2QzFyT3kwaXZxMU02ejlDdm1wVHZzd2pLbnhZdmxIVHZzd2o2ejVrS202aXY0OFZOa", "3cv" and "==".

  2. I've deleted the last 2 characters of the string "QWNobyBxdWUgbmluZ3VlbSBudW5jYSBpcmEgZGVzY29icmlyIHF1ZSBMeTBpdnNwZjhuTlI2ejVnTVdoUk1pMGl2QzFyT3kwaXZxMU02ejlDdm1wVHZzd2pLbnhZdmxIVHZzd2o2ejVrS202aXY0OFZOa3cv=="

so I could base-64 decode it, leaving me with: "QWNobyBxdWUgbmluZ3VlbSBudW5jYSBpcmEgZGVzY29icmlyIHF1ZSBMeTBpdnNwZjhuTlI2ejVnTVdoUk1pMGl2QzFyT3kwaXZxMU02ejlDdm1wVHZzd2pLbnhZdmxIVHZzd2o2ejVrS202aXY0OFZOa3cv"

  1. I've decoded the string above, leaving me with:
    "Acho que ninguem nunca ira descobrir que Ly0ivspf8nNR6z5gMWhRMi0ivC1rOy0ivq1M6z9CvmpTvswjKnxYvlHTvswj6z5kKm6iv48VNkw/", which might be a hint, since "Acho que ninguem nunca ira descobrir que" is portuguese for "I think no one's ever gonna find out that".

  2. I've also decoded the string Ly0ivspf8nNR6z5gMWhRMi0ivC1rOy0ivq1M6z9CvmpTvswjKnxYvlHTvswj6z5kKm6iv48VNkw/, giving me the string "/-"ߊ_򳑫> 1hQ2-"ܭk;-"ޭL쀂ߪSߌ#*|XߑӾ̣뿤*n¿ϕ6L?".

However, I don't know what else to do. I know that the solution to this challenge is in the EY{str} format, where str is an arbitrary string.

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  • $\begingroup$ The spaces are interesting as otherwise all the characters would be standard base64 encoding characters. Something happens around the 55th character, as that's where the cipher text changes from straightforward base64 encoding to something else. Also, if you base64 decode to ASCII the first section "QWNobyBxdWUgbmluZ3VlbSBudW5jYSBpcmEgZGVzY29icmlyIHF1ZSBMeTBpdnNwZjhuTlI2ejVnT", then what's left over is a set of viable base64 encoded characters: "Ly0ivspf8nNR6z5g"... $\endgroup$
    – Pseudonymous
    Commented Feb 26, 2018 at 16:05
  • 1
    $\begingroup$ Hmmm the decoded string uses Korean characters for sure (I'm Korean). It also uses a Greek letter "phi" and an upsidedown question mark found in Spanish. I'm guessing some of the letters look Japanese/Chinese, but I'm not very familiar with unicode. $\endgroup$
    – Prince North Læraðr
    Commented Mar 7, 2018 at 23:34
  • $\begingroup$ I think it's a directory name, but I believe I'm never going to be able to know if I'm right. $\endgroup$
    – 2shy2sayHi
    Commented Mar 21, 2018 at 2:15

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