Self-Hosted Crypto

Challenge

Solution

Convert content from file encrypted to Hex

Then convert to Decimal, so I get an array of numbers

115 121 110 116 136 78 108 111 65 113 108 86 113 64 65 46 62 46 138 10

And here is the pseudocode from the file giving by challenge

After reading, I wrote a short python script to calculate.

list = [115, 121, 110, 116, 136, 78, 108, 111, 65, 113, 108, 86, 113, 64, 65, 46, 62, 46, 138, 10]

out = []
for number in list:
    number = number - 13
    out.append(number)

print(*out)

It just minus each number by 13, then convert them to ASCII and get the flag.
Flag

flag{A_b4d_Id34!1!}

Original writeup (https://github.com/TwentySick/CTF/tree/main/2022/HackPack%20CTF/reverse_engineering/self-hosted_crypto).