我在用Python写一个简单的密码程序（Python新手，加密更新），用户帐户和密码保存在字典中的文件中。我用Fernet模块加密密码。添加用户工作正常，但当我试图解密密码时，我得到 cryptography.fernet.InvalidToken 错误，所以问题应该与密钥有关，虽然我看不出我做错了什么
代码片段：

def generate_master_key():
    my_key_file = "/path/to/passwordfile"
    if os.path.exists(my_key_file):
        with open(my_key_file, 'rb') as myfile:
            master_key = myfile.read()
    else:
        master_key = Fernet.generate_key()
        with open(my_key_file, 'wb') as myfile:
            myfile.write(master_key)
    return master_key
    del master_key

PASSWORDS = json.load(open('accounts'))
key = generate_master_key()
cipher_suite = Fernet(key)

def encrypt(s):
    return cipher_suite.encrypt(base64.encodestring(bytes(s, encoding="ascii")))

def decrypt(token):
    return cipher_suite.decrypt(base64.encodestring(bytes(token, encoding="ascii")))

def add_user():
    print('What is the name of the account you would like to add?')
    account = input()
    print('What is the password of {}?'.format(account))
    pw = getpass.getpass()
    PASSWORDS[account] = encrypt(pw).decode('ascii')
    json.dump(PASSWORDS, open('accounts', 'w'))

def get_password():
    account = sys.argv[1]
    if account in PASSWORDS:
        pyperclip.copy(decrypt(PASSWORDS[account]))
        print('Password for {} copied to clipboard'.format(account))
    else:
        print('There is no account named {}'.format(account))

字符串