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# System prepended metadata

title: Cyber Security Final
tags: [class notes]

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# Cyber Security Final

### 1. 網路安全威脅與需求

### 2. 加密技術
>     對稱 
>     DES : permutation> LPT+RPT> 16bit round key> rejoin and permutation
>         key is too short, 雪崩效應, decrypty just unwind steps
>       
>     AES : substitude byte> shift row> mix column> add round key
>           128-bit data, 128/192/256-bit keys
>     非對稱 
>     RSA : based on exponentiation in a finite (Galois) field over integers modulo a prime
>     任挑兩個大質數p及q ，將pq相乘得n 且求n的尤拉商數ø(n)=(p-1)(q-1)，
>     selecting at random the encryption key e where 1<e<ø(n), gcd(e,ø(n))=1 
>     find decryption key d which e.d=1 mod ø(n) and 0≤d≤n ，令(e,n)為公開金鑰，公告周知，(d,n)為私密金鑰，謹慎保管。
>     ECC
    
    雜湊函數

    數位簽章 : draw the graph will help you understand
        MAC
        digital signatures provide the ability to: 
            1.verify author, date & time of signature
            2.authenticate message contents 
            3.be verified by third parties to resolve disputes
### 3. Classical Encryption: Ciphers ()
##### Caesar
<font color="#f00">[reference]</font> each letter by shifting Xth letter on 
<font color="#0f0">[break]</font> only have 26 possible ciphers, could simply try each in turn
##### Monoalphabetic
<font color="#f00">[referece]</font> rather than just shifting the alphabet, could shuffle (jumble) the letters arbitrarily
<font color="#0f0">[break]</font> human languages are redundant, calculate letter frequencies for ciphertext
##### Playfair
<font color="#f00">[reference]</font> a 5X5 matrix of letters based on a keyword fill in letters of keyword fill rest of matrix with other letters, I and J are in the same grid. 
<font color="#0f0">[break]</font>
##### Vigenere
<font color="#f00">[reference]</font> 對位移方式Ci=Pi+Ki (mod26) or 對照表
<font color="#0f0">[break]</font>
##### Autokey
<font color="#f00">[reference]</font> ideally want a key as long as the, Vigenère proposed the autokey cipher with keyword is prefixed to message as key message, 金匙不夠長，用明文來代替；這種加密方法叫做明文相依加密器，即加密方法因明文而易，最不易被破解。
<font color="#0f0">[break]</font>
##### Row Transposition
<font color="#f00">[reference]</font>write letters of message out in rows over a specified number of columns, then reorder the columns according to some key before reading off the rows
<font color="#0f0">[break]</font>
##### Rail Fence
<font color="#f00">[reference]</font> write message letters out diagonally over a number of rows, then read off cipher row by row
<font color="#0f0">[break]</font>
### 4. SSL (Secure Socket Layer) + HTTP = HTTPS --> Handshake protocol
    transport layer security service for application layer(https)
    originally developed by Netscape, subsequently became Internet standard known as TLS
    uses TCP to provide a reliable end-to-end service
    SSL has two layers of protocols - Change Cipher Spec Protocol & Record Protocol
    Handshake protocol: phase 1: establish connect, say hello to each other
                        phase 2: server authentification
                        phase 3: client authentificate
                        phase 4: change cypher suite and finish handshake 
    -->keys needed for Cipher Spec.<--
         Client write MAC secret key, 
         Server write MAC secret key,
         Client write secret key,
         Server write secret key,
         Client write IV,
         Server write IV
### 5. SET --> Dual Signature (Purchase Request - Customer & Merchant)
    is a communications protocol standard for securing credit card transactions over networks
    訂單產生將訂單與帳單hash完後串接在一起，再hash一次並做簽章銀行看不到訂單資訊 商家看不到帳單資訊, 
### 6. PGP --> 滿足了四個條件 
           --> final range

### 7. Session Key Exchange -> RSA , D-H , Fixed D-H, D-H
     RSA , 
     D-H , 
     Fixed D-H
### 8. POST - Quantum Cryptograph 
		1. 最接近向量問題
		2. Knapsack cryptosystem
###### tags: `class notes`