system: You are an expert security code reviewer. You will be shown a source code file along with a multiple-choice question listing several function or class names from that file. Your task is to identify which one contains the specified CWE vulnerability.

OUTPUT FORMAT: Respond with the single letter of the correct option, wrapped in \boxed{...}. Example: `\boxed{B}`. Output the boxed letter ONLY -- no explanation, no other text.

user: ```python
import socket
import struct
import sys
import threading
import json
import time
import ssl

PORT = 1234
HEADER_LENGTH = 2
ime = ""


def setup_SSL_context():
  #uporabi samo TLS, ne SSL
  context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
  # certifikat je obvezen
  context.verify_mode = ssl.CERT_REQUIRED
  #nalozi svoje certifikate
  context.load_cert_chain(certfile=ime+'.pem', keyfile=ime+'key.pem')
  # nalozi certifikate CAjev (samopodp. cert.= svoja CA!)
  context.load_verify_locations('server.pem')
  # nastavi SSL CipherSuites (nacin kriptiranja)
  context.set_ciphers('AES128-SHA')
  return context

def receive_fixed_length_msg(sock, msglen):
    message = b''
    while len(message) < msglen:
        chunk = sock.recv(msglen - len(message))  # preberi nekaj bajtov
        if chunk == b'':
            raise RuntimeError("socket connection broken")
        message = message + chunk  # pripni prebrane bajte sporocilu

    return message


def receive_message(sock):
    header = receive_fixed_length_msg(sock,
                                      HEADER_LENGTH)  # preberi glavo sporocila (v prvih 2 bytih je dolzina sporocila)
    message_length = struct.unpack("!H", header)[0]  # pretvori dolzino sporocila v int

    message = None
    if message_length > 0:  # ce je vse OK
        message = receive_fixed_length_msg(sock, message_length)  # preberi sporocilo
        message = message.decode("utf-8")

    return message


def send_message(sock, message):
    encoded_message = message.encode("utf-8")  # pretvori sporocilo v niz bajtov, uporabi UTF-8 kodno tabelo

    # ustvari glavo v prvih 2 bytih je dolzina sporocila (HEADER_LENGTH)
    # metoda pack "!H" : !=network byte order, H=unsigned short
    header = struct.pack("!H", len(encoded_message))

    message = header + encoded_message  # najprj posljemo dolzino sporocilo, slee nato sporocilo samo
    sock.sendall(message)


# message_receiver funkcija tece v loceni niti
def message_receiver():
    global ime
    while True:
        if ime != "":
            msg_received = receive_message(sock)
            try:
                message = json.loads(msg_received)
                source, destination, message, time = message.values()
                if source.upper() != ime.upper():
                    print(time + " <" + source + "> " + message)  #izpis
            except:
                 pass

#prijava
while ime == "":
    ime = input("Vpiši ime: ")


# povezi se na streznik
print("[system] connecting to chat server ...")
my_ssl_ctx = setup_SSL_context()
sock = my_ssl_ctx.wrap_socket(socket.socket(socket.AF_INET, socket.SOCK_STREAM))
sock.connect(("localhost", PORT))
print("[system] connected!")

# zazeni message_receiver funkcijo v loceni niti
thread = threading.Thread(target=message_receiver)
thread.daemon = True
thread.start()



# pocakaj da uporabnik nekaj natipka in poslji na streznik
print()
while True:
    try:
        destination = ""
        user_input = input("")
        message_format = {
            "source": "",
            "destination": destination.strip(),
            "message": user_input,
            "time": time.strftime("%H:%M:%S")
        }
        json_message = json.dumps(message_format)

        send_message(sock, json_message)
    except:
        print("<system> ERROR: Wrong input!")

```

Which of the following functions or classes contains a `CWE-327: Use of a Broken or Risky Cryptographic Algorithm` vulnerability?

  A) message_receiver
  B) setup_SSL_context
  C) send_message
  D) receive_fixed_length_msg
Answer: B