Rating:
After checking the given files we made a script that gave the flag.
```python
from itertools import cycle
# Given ciphertext file
ciphertext_file = "ct"
# Read the ciphertext
with open(ciphertext_file, "rb") as f:
ct = f.read()
# We know the flag starts with "uiuctf{"
known_plaintext = b"uiuctf{"
# XOR the first 7 bytes of ciphertext with the known plaintext to get the key
partial_key = bytes(ct_byte ^ pt_byte for ct_byte, pt_byte in zip(ct[:7], known_plaintext))
# The key is 8 bytes long, we can deduce the 8th byte by XORing the 8th byte of the ciphertext with the 8th character of the flag
# Here we assume the 8th character of the flag is the first character after '{' which could be any valid character, we will brute-force it
for i in range(256):
potential_key = partial_key + bytes([i])
decrypted_flag = bytes(ct_byte ^ key_byte for ct_byte, key_byte in zip(ct, cycle(potential_key)))
if decrypted_flag.startswith(b"uiuctf{") and decrypted_flag.endswith(b"}"):
print(decrypted_flag.decode())
break
```
Flag: `uiuctf{n0t_ju5t_th3_st4rt_but_4l50_th3_3nd!!!!!}`
