Initially, I went in a completely different direction by converting to a decimal and then mapping to a base64 number, but I learned more about Base64’s input scheme while solving this. Eventually I figured out the solution, it wasn’t mathematical, it required learning about Base64.
The Problem
The challenge is to map this:
49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d
To this Base64 value:
SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t
The Solution
The solution became clearer when I read hint at the bottom:
Always operate on raw bytes, never on encoded strings. Only use hex and base64 for pretty-printing.
I converted the hex string into raw bytes using binascii where I say the message:
I’m killing your brain like a poisonous mushroom
Charming. I then read the base64 library’s encode function which seemed to be using binascii as well. So I used that to convert to base64, and cleaned the result by converting it to a string.
The Code
import binascii
input = "49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d"
expected = "SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t"
# Convert the hex to bytes
bytes = binascii.a2b_hex(input)
print(bytes)
# => b"I'm killing your brain like a poisonous mushroom"
# Pass the bytes to base64
base64 = binascii.b2a_base64(bytes, newline=False)
print(base64)
# => b'SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t\n'
# Convert to a string
cleaned_result = base64.decode()
print(cleaned_result)
# => SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t
print(cleaned_result == expected)
# => True