just guessed the decryption recipe on one try. very very easy.

need to try more and more as a hint - image to txt -> decode -> decode

Nice!

How is one supposed to figure out the ROT13

Interesting challenge took me some time to get the last step.

Learn to use CyberChef. 3 recipes and solved.

Amazing!

cool :)

How is one supposed to know that there's ROT13 letter substitution?

CAREFUL, SPOILERS:

I highly recommend Cyberchef to do this one. You can use the function "Parse QR-Code" to solve the first step. For step 2 you need to decode it. Try and figure out which format uses an "=" sign to fill up triplets at the end. The last one to me is actually quite hard to find out, if you don't know what to do. But you can see that the position of the ":" and the "_" already kinda makes sense. Maybe the letters just need some rotation?

How do we get to know about double decrypts ?

I enjoy clever hints, but we really need to go by the unspoken rule of not sharing flags publicly. Severus did a pretty good job on this!

cyber chef was enough for me here (from qr code + from base64 + and rot13) and finally u get the flag

I pasted the encoded message into google and scrolled past all the "CTFlearn QR code answers" and one of the sites said rot13 decoder. thats how I figured it out.

use this https://www.dcode.fr/cipher-identifier