MIS Week One 总结

ＤＡＹ　1 -----Distributed System

• what is distributed system?
  “One in which components located at networked computers communicate and co-ordinate their actions only by passing messages.”

• Issue with distributed systems

  1. Concurrency
     a . Tasks could get out of order.
     b. Tasks could require the same resources.
     c. Tasks could “starve” other tasks.

  2. No global clock
     a. No easy way to know which event happened first.
     b. No easy way to assign “priority”.

  3. Independent failures
     a. Each component could fail.
     b. Different failures could have different consequences.

• Byzantine Generals(两个蓝色的攻击一个红色的，只有一起攻击才能赢)

• Dining Philosophers(哲学家围在一桌吃饭)

• Models of distributed computing

  1. Physical models —Abstract away details show only the machines and how they communicte.

  2. Architectural models— What entities communicate? How do they communicate? What roles/responsibilities do they have? Where are they placed physically?

  3. Fundamental models

ＤＡＹ　３

• Key Management----首先面临的问题是非对称加密虽然安全但是浪费时间。

  - session key——用一个非对称加密方法传送对称加密的密钥
  
  - 可信任的第三方（KDC）——If we trust a "third party" to generate keys we communicate with them to get the session key.Now we only need to establish a secure asymmetric connection to trusted party.
  

  

3. 认证

• 双重加密——First with the private key of the sender.Second with the public key of the receiver.
• digital signing——Authentication without encryption

4. 中间人能够在非对称加密交换密钥时做文章

5. SSL/TLS:

• Protocol must:
  a. Exchange and check certificate of website
  b. Asymmetric RSA/Diffie-Hellman send session key
  c. Symmetric for encoding session