A new crypto challenge!

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Type: Crypto
Description: Decrypt the cipher-text below to find the flag.

TGPRGWTADEKI HI3OYNODONAT ES4LOCIINTB} FC4LURSDTHO_ LO1IRYAEEIU_ AM{NOPBAVNT_

Format: Enter the flag with no spaces.  The flag looks like:

COMP3441{...}

So first thing’s first is to figure out a pat-wait I’ve seen this before…
It’s as if I’ve done this bef-oh.

Source: github.com/featherbear/…/interleave.py

I’ve once written a script to both encode and decode these sorts of ‘interleave’ ciphers.
(I’ve got no clue what they’re really called…)

Basically, you take the first letter of each word,
then take the second letter of each word, then take the third letter of each word, then take the fourth letter of each word, and keep going until you get the answer…

Let’s try that shall we?

TGPRGWTADEKI
HI3OYNODONAT
ES4LOCIINTB}
FC4LURSDTHO_
LO1IRYAEEIU_
AM{NOPBAVNT_

The first column spells out THEFLA.

TGPRGWTADEKI
HI3OYNODONAT
ES4LOCIINTB}
FC4LURSDTHO_
LO1IRYAEEIU_
AM{NOPBAVNT_

The second column spells out GISCOM.

TGPRGWTADEKI
HI3OYNODONAT
ES4LOCIINTB}
FC4LURSDTHO_
LO1IRYAEEIU_
AM{NOPBAVNT_

The third column spells out P3441{.

If we chuck those three phrases together… we get THEFLAGISCOMP3411{.
So rinse and repeat, until we finally get the answer: COMP3441{ROLLINGYOUROWNCRYPTOISABADIDEADONTEVENTHINKABOUTIT}

Easy!
(We disregard the _ characters, as they are just there for padding)

But, what does the answer mean?

“ROLLING YOUR OWN CRYPTO IS A BAD IDEA DONT EVEN THINK ABOUT IT”, huh!?

In essence; don’t try to come up with your own cryptographic method - because it’s probably dumb and simple to break.

… you might come up with a super fancy and weird encryption algorithm - only to realise that breaking it is simpler than creating it..

Actual smart people have spent many many hours working on the cryptographic algorithms that we use everywhere these days.
Yes, there are vulnerabilities in the implementation - but on the whole, it’s still better than something that I could come up with… :)