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Epic Poem Writeup

Affinity 2019 - crypto 500 - 25 solves

Alicja sent text for her friend translator Bob. Because Alicja likes privacy, she encrypted text with key. Bob translate the text and sent back to her also in encrypted form. Can you find the key?

Guessing and getting the flag

Since the challenge asked to find the key, I first use the flag format. The flag starts with AFFCTF{. I guessed that the cryptosystem is just a simple xor cipher.

By xoring AFFCTF{ with enc2, I get some readable plaintext: Litwo! . I searched the plaintext in google, and guessed the further plaintext assuming the plaintext is from here. Xor it back with enc2 to get the key.

I get the flag:

AFFCTF{M4nY_t1m3_PaD_1$_b@d__!!!}

exploit driver code: solve.py

Original problem: enc1, enc2