Gibberish Solution

by Christopher Xue

FLAG: carlgauss

Seeing “aaaa” pop up, we guess that it represents the four letter word “flag”, and the cipher is a vigenere. So to decrypt, we must add a key to each letter using modular addition (a = 0, z = 25). It looks like this key has “flag” in it since adding “flag” to “aaaa” yields “flag”. We can just try using “flag” as the key, or we can also notice that the “aaaa”’s occur at positions 20 and 64 (counting only the letters, not the spaces or punctuation) which has gcd 4, implying the length of the key divides 4 and so the key is “flag”.

We add “flag” to the letters in order, and the plaintext is revealed to be “this blurb contains the flag. here is a meaningless line. another one. hello. the flag is carlgauss. more nonsensical lines.” Hence, the flag is “carlgauss”.