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misc-zero-width-characters.md

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Nothing In Between

  • Event: ForeverCTF
  • Problem Type: Misc
  • Point Value / Difficulty: Medium
  • (Optional) Tools Required / Used:

Steps​

Step 1

If you try to copy the flag and submit it, it won't work. But, if you copy the flag into something like vim (or this tool, or this tool or read the hint :) ) you will see that there are extra characters in there:

Step 2

Those characters are zero width characters that cannot be seen when printed. You can see that there are two of them that are alternating: 200B (zero width space) and 200C (zero width non-joiner). If you replace all the 200B characters with 0 and the 200C characters with 1, the hidden text will now look a lot like binary that's representing ASCII characters.

Step 3

When you convert the binary to ASCII (this tool is nice for that), you should get the real flag.