# 網路與資訊安全概論第一次作業
> 姓名: 楊明寰
> 學號: 1103334
## Chap. 1
* Review Questions
* 1.3
* Passive attack:
1. Release of message contents
2. Traffic analysis (Analyze contents or behavior)
* Active attack:
1. Masquerade (By pretending to be somebody)
2. Replay (Capture user’s privacy info such as password and then retransmit the info to server)
3. Data Modification
4. Denial of service
* 1.4
1. Authentication (Assure that a communication is authentic)
2. Access Control (To make sure something has the right to access or not to another one)
3. Data Confidentiality (Protect transmitting data from passive attacks)
4. Data Integrity (Protect from being unauthorized modification from passive attacks)
5. Nonrepudiation (Make sure that sender or receiver cannot claim that didn’t receive the data)
6. Availability Service (Protect a system to ensure its availability)

* 1.7
1. Keyless (None of key is used during transmitting)
2. Single-Key
3. Two-Key (Use private and public key)

## Chap. 3
* Review Questions
* 3.8
Because there’s only 26 alphabets, we only need to try 1~25 place(s) then we would find the plain text.
* Home Reading
* what is Substitute Technique
It’s a technique to replace the word to another word to encrypt plain text to ciphertext. For example, Caesar cipher substitution.