# Define the key to use for the XOR operation
key = "mysecretkey"

# Define the original message to be encrypted
message = "Hello, world!"

# Convert the key and message to binary format
binary_key = key.encode('utf-8')
binary_message = message.encode('utf-8')

# Perform the XOR operation on the binary message using the binary key
ciphertext = bytearray(len(binary_message))
for i in range(len(binary_message)):
  ciphertext[i] = binary_message[i] ^ binary_key[i % len(binary_key)]

# Print the resulting ciphertext
print(ciphertext)