Computer Security (1)

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1. What problems does security solve.

Ans: security mainly addresses four types of requirements

: Hash algorithm Digital Signature

// Confidentiality: symmetric/asymmetric encryption DES AEs/RSA // Authentication/authentication: hash algorithm (MD5 sha1) // Integrity: hash algorithm (MD5 sha1) // Undeniable: Digital Signature

2. Password

Password in life: letter encryption and inverted writing...

In general, password can be defined for any rule, but a general password must have a high security level;

The basic skills commonly used by computers are: change the password to the password product password (the first two are duplicated)

3. Composition of cryptographic techniques: algorithm + key

4. symmetric encryption/asymmetric encryption

For symmetric encryption, there is only one key.

For non-pair encryption, the encryption key is called the private key, and the decryption key is called the Public Key (as shown in the figure below ).

5. Application of symmetric encryption: des/AES

Des: Data Encryption Standard (DES) is a block password encrypted using a 56-bit symmetric algorithm.

Disadvantage: The key length is 56 and can be cracked by brute force.

AES: Advanced Encryption Standard (AES). The block length of AES is fixed to 128 bits, and the key length can be 128,192 or 256 bits. keys used during encryption are generated by the Rijndael key generation scheme. because the length of the key is longer and the length of the key is not fixed, the Advanced Encryption Standard has become one of the most popular algorithms in symmetric key encryption.

The advantage of symmetric encryption is that the speed and efficiency of encryption and decryption are highly applicable to the big data era.

The disadvantage is that it is low in security and can be decrypted as long as the key is intercepted.

6. Application of asymmetric encryption: RSA

RSA: RSA is an asymmetric encryption algorithm. RSA was proposed in 1977 by Ronald Rivest, Adi sarmore (Adi Shamir), and Leonard Adleman. Both of them were working at the Massachusetts Institute of Technology. RSA is the combination of the first letters of the three surnames.

The RSA algorithm is difficult Based on factorization: the difficulty of Factorization large integers determines the reliability of the RSA algorithm. In other words, the more difficult it is to decompose a large integer, the more reliable the RSA algorithm is.

Another important mathematical basis for the publication of an algorithm is the difficulty of calculating the discrete logarithm based on a large prime number;

The RSA Public/Private Key must be at least bits in length and several times of symmetric encryption;

Asymmetric encryption features high security.

The disadvantage is that encryption and decryption speed is extremely low, and it is not suitable for applications in the current big data era.

7. Confidential sessions of traditional computers:

Use symmetric encryption to encrypt the original text and perform asymmetric encryption on the encryption key.

In general, the advantages and disadvantages of symmetric/asymmetric encryption are complementary, which solves the actual application problems.