Firewall, VPN, WAN, and client are discussed as methods for strong encryption and security. A firewall protects networks from unauthorized access while allowing authorized communications. A VPN uses the public internet to provide remote or individual secure access to an organization's network. A WAN covers a broad area like across cities or countries. A client accesses remote server services over a network. References for further information are also provided.

1. How Encryption for Strong Security
Works
● Firewall
● VPN
● WAN
● Client

2. Firewall
● A firewall is a part of a
computer system or network
that is designed to block
unauthorized access while
permitting authorized
communications. It is a
device or set of devices that
is configured to permit or
deny network transmissions
based upon a set of rules
and other criteria.

3. VPN(Virtual private network)
● A virtual private network
(VPN) is a computer
network that uses a public
telecommunication
infrastructure such as the
Internet to provide remote
offices or individual users
with secure access to their
organization's network.

4. WAN(Wide Area Network)
● A wide area network
(WAN) is a computer
network that covers a
broad area (any
network whose
communications links
cross metropolitan,
regional, or national
boundaries).

5. Client
● A client is an application or
system that accesses a
remote service on another
computer system, known as
a server, by way of a
network.
● Client and server can run on
the same machine and
connect via Unix domain
sockets.

6. Reference
● Wikipedia
http://ja.wikipedia.org/wiki
● Google
http://www.google.co.jp