The Impossible Challenge

Date: 21, June, 2021

Author: Dhilip Sanjay S

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• We need a password to access the flag inside the zip file.

• So the password must be hidden. May be in that encoded text!

• P.S: Bruteforcing the password didn't work

Decoding

• Decode the text using Cyberchef:

qo qt q` r6 ro su pn s_ rn r6 p6 s_ q2 ps qq rs rp ps rt r4 pu pt qn r4 rq pt q` so pu ps r4 sq pu ps q2 su rn on oq o_ pu ps ou r5 pu pt r4 sr rp qt pu rs q2 qt r4 r4 ro su pq o5

Cyberchef

• So, what's infront of our eyes???

Zero Width Characters

• On pasting the title of the challenge in Cyberchef, we find some dotted characters. Those are called as zero width characters

Cyberchef

• Zero width Non-joiner

• Zero width Space

Zero width Identifiers

• Cyberchef

• Grammarly will underline the words even though if they have the right spelling!! (Because of those hidden characters)

Zero width tools

• Steganographr

• Unicode Steganography

• Zero width Fingerprinting

Flag

Unicode Steganography

• Use the password to extract the zip:

$ unzip Impossible.zip 
Archive:  Impossible.zip
[Impossible.zip] flag.txt password: 
  inflating: flag.txt                
$ cat flag.txt 
You have solved the Impossible Challenge! Here is your flag THM{REDACTED}

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References

• Null Byte Article