DAY 1

Here is the challenge description:

Output of the start.txt is as follows:

🔹 Step 1: Binary → ASCII

Each group of 8 bits represents one ASCII character.

Example:

00110101 → 53 (decimal) → '5' 00111001 → 57 → '9' 00110011 → 51 → '3'

Doing this for the entire sequence converts the binary into a readable ASCII string:

59334e6b6531637a624747774e664f474644533138334d4639685a48597a546a64664d6a41794e583033d

So after Step 1, we have a hex-looking string (characters 0–9 and a–f).

🔹 Step 2: ASCII → Hex decoding

That ASCII output is actually hexadecimal.

Hex pairs represent bytes:

59 → 'Y' 33 → '3' 4e → 'N' 6b → 'k' 65 → 'e' 31 → '1' 63 → 'c' 7a → 'z' ...

Decoding the entire hex string gives:

Y3NkezVlbGNvbWVfOGFDS180MF9hZHYzTjdfejAyNX0=

Now this clearly ends with = — a big hint 👀
That means…

🔹 Step 3: Base64 decoding

The string is Base64-encoded.

Decoding it produces:

csd{W3lc0m3_8aCK_70_adv3N7_2025}