system: You are an expert security code reviewer. You will be shown a source code file. Your task is to name the single function or class that contains the specified CWE vulnerability.

OUTPUT FORMAT: Respond with the exact function or class name (no parentheses, no qualifiers, no module prefixes), wrapped in \boxed{...}. Example: `\boxed{salted_hmac}`. Output the boxed name ONLY -- no explanation, no other text.

user: ```python
#!/usr/bin/env python
# -*- coding: utf-8 -*-


import tkinter as tk
from tkinter import ttk
import tkinter.simpledialog

import os
import paramiko
from glob import glob
from configparser import ConfigParser

__author__ = ['Enrico Giampieri', 'Nico Curti']
__email__ = ['enrico.giampieri@unibo.it', 'nico.curti2@unibo.it']


class _Config (ttk.Frame):

  _required_infos = [('CONNECTION', 'host'), ('CONNECTION', 'user'), ('CONNECTION', 'keyfile'),
                     ('REMOTE', 'base_dir'), ('REMOTE', 'done_subdir'), ('REMOTE', 'todo_subdir')]

  def __init__ (self, *args, **kwargs):

    super(_Config, self).__init__(*args, **kwargs)

    self._parser = ConfigParser()
    self._cfg_file = ''

    # try to load the first available .ini file in the
    # current path
    available_cfg = glob('*.ini')

    if available_cfg:
      self._cfg_file = available_cfg[0]
      self._parser.read(self._cfg_file)

    # add log
    self._winfos = tk.scrolledtext.ScrolledText(self, width=60, height=25)
    # add widgets
    self._wcfg = tk.Button(self, text='Load', command=self._cfg_cb)
    self._wscp = tk.Button(self, text='Keygen', fg='Red', command=self._set_pwd_cb)

    # widget on grid
    self._winfos.grid(column=0, row=2, columnspan=3, rowspan=4)
    self._wcfg.grid(column=1, row=0)
    self._wscp.grid(column=0, row=0)

    # widget values
    self._winfos.insert(tk.INSERT, self._template_log())


  def _cfg_cb (self):

    local = os.path.abspath('.')
    self._cfg_file = tk.filedialog.askopenfilename(initialdir=local, title='Select config file',
                                                   filetypes=(('cfg', '*.ini'),
                                                              ('all files', '*.*'))
                                                   )

    try:
      self._parser.read(self._cfg_file)
    except Exception as e:
      tk.messagebox.showerror('Error', e)
      return

    self._winfos.delete(1., tk.END)
    self._winfos.insert(tk.INSERT, self._template_log())


  def _template_log (self):
    '''
    Template of the log
    '''

    try:
      self._check_config()
      values = sum([[self._cfg_file], list(self.connection_params.values()), list(self.remote_params.values())], [])
    except ValueError:
      values = ('', ) * 7

    return 'config file: {0}\n\n'\
           '[CONNECTION]\n' \
           'host={1}\n' \
           'user={2}\n' \
           'keyfile={3}\n\n'\
           '[REMOTE]\n' \
           'base_dir={4}\n' \
           'done_subdir={5}\n' \
           'todo_subdir={6}\n\n'.format(*values)

  def _check_config (self):
    '''
    Check if the config file has the minimum required sections
    '''

    for section, key in self._required_infos:
      if not self._parser.has_option(section, key):
        raise ValueError('Key not found')

    return True

  def _set_pwd_cb (self):
    '''
    Set the password for the remote server and copy the password as remote key
    '''
    if not self._cfg_file:
      tk.messagebox.showerror('Error', 'No config file loaded!')
      return

    username = self._parser.get('CONNECTION', 'user')
    hostname = self._parser.get('CONNECTION', 'host')
    keyfile  = self._parser.get('CONNECTION', 'keyfile')
    password = tk.simpledialog.askstring('Password', 'Enter password:', show='\u2022', parent=self)


    if os.path.exists(keyfile):
      tk.messagebox.showwarning('Warning!',
                                'The keyfile already exists.')
      return

    # generate a new ssh key using ssh-keygen
    key = paramiko.RSAKey.generate(4096)
    key.write_private_key_file(keyfile)  # print private key
    pub_key = '{0} {1} {2}@{3}\n'.format(key.get_name(), key.get_base64(), username, hostname)

    try:

      ssh = paramiko.SSHClient()
      ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
      ssh.connect(hostname, port=22,
                  username=username,
                  password=password)

      # create .ssh dir
      stdin, stdout, stderr = ssh.exec_command('mkdir -p .ssh')
      if stdout.channel.recv_exit_status():    # status is not 0
        tk.messagebox.showerror('Error', str(e))
        return
      # append authorized_keys

      stdin, stdout, stderr = ssh.exec_command('echo "{}" >> .ssh/authorized_keys'.format(pub_key))
      if stdout.channel.recv_exit_status():    # status is not 0
        tk.messagebox.showerror('Error', str(e))
        return

      # create directories
      base_dir = self.remote_params['base_dir']
      stdin, stdout, stderr = ssh.exec_command('mkdir -p {}'.format(base_dir))
      if stdout.channel.recv_exit_status():    # status is not 0
        tk.messagebox.showerror('Error', str(e))
        return

      stdin, stdout, stderr = ssh.exec_command('mkdir -p {}/{}'.format(base_dir, self.remote_params['todo_subdir']))
      if stdout.channel.recv_exit_status():    # status is not 0
        tk.messagebox.showerror('Error', str(e))
        return

      stdin, stdout, stderr = ssh.exec_command('mkdir -p {}/{}'.format(base_dir, self.remote_params['done_subdir']))
      if stdout.channel.recv_exit_status():    # status is not 0
        tk.messagebox.showerror('Error', str(e))
        return

      ssh.close()

    except Exception as e:
      print(repr(e))
      tk.messagebox.showerror('Error', str(e))
      return

  @property
  def connection_params (self):
    '''
    Return the connection informations as dict
    '''
    return dict(host=self._parser.get('CONNECTION', 'host'),
                user=self._parser.get('CONNECTION', 'user'),
                keyfile=self._parser.get('CONNECTION', 'keyfile'),
                )

  @property
  def remote_params (self):
    '''
    Return the information of the remote host as dict
    '''
    return dict(base_dir=self._parser.get('REMOTE', 'base_dir'),
                done_subdir=self._parser.get('REMOTE', 'done_subdir'),
                todo_subdir=self._parser.get('REMOTE', 'todo_subdir'),
                )

  @property
  def config(self):
    return self._cfg_file

```

Name the function or class in this code that contains a `CWE-295: Improper Certificate Validation` vulnerability.
Answer: _set_pwd_cb