The ELF executable (rev3_32) we receive for this challenge takes a string as input, performs some operations on it and finally compares it to the following hardcoded string egzloxi|ixw]dkSe]dzSzccShejSi^3q. If the two strings match, the program prints a success message.

Let’s have a look at the encode function, which can be seen in the screenshot below:


What this function basically does is it takes each input character XOR 9 and subtracts 3 from the result. In order to obtain the decoded string, we just use a small Python script which reverts the encoding.

encoded = "egzloxi|ixw]dkSe]dzSzccShejSi^3q" 
decoded = ""

for c in encoded:
  dc = ord(c) + 3
  dc =  dc ^ 9
  decoded += str(chr(dc))


The decoded string is also our flag.