[Cryptography] Network Security Part I

(1) Hub, Switch, Router, Gateway

Hub: like center
       it can not choose which directions to go

  Switch: choose which direction they send in the LAN

  Router: forward from LAN to LAN

  Gateway: can communicate between LAN and other networks


  Gateway vs Router:
           

from here

1. 概念上不是一回事。路由器是負責選擇資料包轉發路徑的裝置；而網關就是充當網絡出口的裝置，相當于上網要經過的關卡。這樣說來，網關就是路由器的一個子子產品而已。
     2. 事實上很多廠家的路由和網關都是一種裝置。叫法不同，是他們根據應用場景來的。
           

(2) Firewalls

special gateway
   protect from inappropriate access
           

(3) Network Protocols

data exchange between computers to communicate and share
           

(4) Network Layer Security

packet switching:
   messages are divided into fixed-size,numbered packets

IP sec:
   goals: secure traffic between two IP systems.
   保證在轉發的路上是安全的
           

(5) Transport Layer Security

SSL secure socket layer
 https: secure communications between browser and server
           

SSL

SSL:
   data exchange and encryption

 SSL session:
     between browser and server
     created by three-hand shake protocol

 SSL connection:
           

(6) IPsec VS SSL

(7) Network Security Threats