Nahamcon 2021
EAXY
We are given a hex like looking data, we upload the file to CyberChef,
From the challenge name we get a hint that it might be XOR, so we try to bruteforce XOR.
For most of keys you get a plaintext in which they have mentioned the index of the each character
for example,The word HELLO , here the letter H will have index 0, and letter E will have 1 and so on.
we write down all the indexes
Assemble them accordingly and we get the following string
666c61677b31366564666365356331323434336236313832386166366361623930646337397d
Which is just a hex string, unhex it and we get the flag
flag{16edfce5c12443b61828af6cab90dc79}
KEY | INDEX
key 30 - 32
key 31 - 5, 14, 21
key 32 - 15, 23,
key 33 - 18,
key 34 - 16, 17
key 35 - 12
key 36 - 6, 20, 27
key 37 - 35
key 38 - 22, 24
key 39 - 31, 36
key 61 - 2, 25, 29
key 62 - 19, 30
key 63 - 10, 13, 28, 34
key 64 - 8, 33
key 65 - 7, 11
key 66 - 0, 9, 26
key 67 - 3
key 6c - 1
key 7b - 4
key 7d - 37
key 30 - 32
key 31 - 5, 14, 21
key 32 - 15, 23