- 2020-06-28 06:51
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<> Basic concepts of network security

<> Introduction to network security

With the development of Internet , The rich information resources of network bring great convenience to users , But it also brings security problems . The essence of network security is to ensure the information security attribute on the network . Information security refers to the hardware of information system , Data in software and its system is protected , It's a computer science , network technique , A comprehensive discipline of communication and cryptography .

Network security includes physical security , Three levels of data information security and network transmission security .

Five basic elements of network information security ：

1. Confidentiality

2. Integrity

3. usability

4. Controllability

5. Auditability

<> Network security strategy and protection system

Network security protection policy refers to the rules that must be followed to ensure a certain level of security protection .

Realize network security , Generally, three kinds of measures are taken ：

1. Information security technology

2. Network security management

3. Network security and law

The current designated network security policy mainly includes five aspects ：

1. Physical security policy

2. Access control policy

3. Firewall policy

4. Information encryption policy

5. Network security management strategy

Network security system is a legal system of network security , Network security management system and network security technology system .

<> Data encryption technology

Password technology is the first thing we think about when we talk about information security , It is to study the transformation of the transmitted information to prevent the third party from stealing the information , Is the core of network security . Here are some common cryptography techniques

<> Classical encryption algorithm

1. Code encryption

An example of this algorithm can be seen ：

Plaintext ： Grandma's yellow dog cubs in three days

ciphertext ： Three days later, the county cabinet went out of the city to clean up

This method is simple and easy to use , But it can only convey the message of foreknowledge , Reuse is not safe .

2. Substitution encryption

This method is to make a rule , Replace each letter in clear text with another , A replacement encryptor is usually required . The famous Caesar shift code in history is this method , Use the first letter after each letter in the alphabet 3 Bit substitution .

Plaintext ：ABCDEFGHIJKLMNOPQRSTUVWXYZ

ciphertext ：defghijklmnopqrstuvwxyzabc

This method is more widely used than code encryption , But it's easy to find the law after using it many times .

3. Transposition encryption

This method does not hide clear text characters , Is to reorder the characters . for example ：

secret key ：6972430815

Plaintext ： Small Zhao take go black skin package hand over to Plum

0 1 2 3 4 5 6 7 8 9

ciphertext ： package Plum Zhao take black go Small to look for skin

6 9 7 2 4 3 0 8 1 5

4. One time cipherbook encryption

This method is based on a random key （key） Compose plaintext , And only once . This method 1882 By Frank · Miller （Frank Miller） find , And still in use today .

When encrypting , Shift or exclusive or calculate the letters in the message according to the numbers in the cipherbook , To encrypt messages . The only way to decrypt is to have the same passbook , Shift letters according to codebook , Or another exclusive or calculation .

Here is an example of bitwise XOR encryption and decryption ：

Encryption process clear text and password bitwise XOR

Plaintext ：101101011011

password ：011010101001

ciphertext ：110111110010

Bitwise XOR of ciphertext and password in decryption process

ciphertext ：110111110010

password ：011010101001

Plaintext ：101101011011

One time password Book encryption can only be used once , It must be at least as long as the encrypted file .

Traditional encryption methods have many limitations , So people came up with other encryption algorithms .

<> Symmetric encryption algorithm

The characteristic of symmetric encryption algorithm is that encryption and decryption use the same set of keys , That is, the encryption and decryption keys are symmetric , The security of symmetric encryption is determined by encryption algorithm and key length . Common encryption algorithms include AES,DES,3DES and IDEA wait . At present, the most used symmetric encryption algorithm is DES and 3DES, Used in individual systems IDEA,RC5 And other algorithms .

DES Algorithm encryption and decryption can use the same algorithm , But the order of the two keys is opposite , System security depends on the security of the key .

3DES In the algorithm , Use two or three keys to encrypt a packet three times , No decipherment has been found except the exhaustive method DES A shortcut to .

<> Asymmetric encryption algorithm

The characteristic of asymmetric encryption algorithm is that encryption and decryption use two different keys , That is, the encryption and decryption keys are asymmetric , Also known as public key cryptosystem PKC. Different from symmetric algorithm , Asymmetric cryptography algorithm will randomly generate two keys according to the digital relationship , A public key used to encrypt plaintext , A private key used to decrypt ciphertext . This method has high security , Key is easy to keep , But the amount of calculation is large , Slow encryption and decryption . The most common is RSA algorithm .

RSA Is the most famous double key cryptosystem , Can be used to encrypt data , It can also be used for digital signature .

RSA algorithm ： Sender wants to communicate , Using asymmetric encryption algorithm to generate a pair of keys , Public key and private key , The receiver encrypts the sender's public key when it receives it , Messages encrypted by the sender's public key can only be decrypted by the sender's own private key .

In the actual system , only need RSA In exchange DES secret key , But with DES To encrypt principal information .

In terms of hardware implementation ,RSA than DES Slow reduction 1000 times , In terms of software implementation ,RSA than DES Slow reduction 100 times .

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