Encryption and decryption

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1. summary

Encryption is divided into One way encryption and Two way encryption

• One way encryption ： One way encryption is irreversible , After the ciphertext is generated, the original content cannot be obtained according to the ciphertext . Therefore, one-way encryption is often used to verify the integrity and originality of the content , Not for security . for example MD5 Algorithm

• Two way encryption ： Bidirectional encryption refers to the generation of ciphertext , It can be decrypted into plaintext . It is usually applied to secure transmission and permission Application . for example RSA Algorithm .

1.1 Introduction to bidirectional encryption

Bidirectional decryption can be roughly divided into Symmetric encryption and Asymmetric encryption
Symmetric encryption ： Encryption and decryption use the same secret key ,
Asymmetric encryption ： Encryption and decryption use different keys , Encryption uses Private key , Decryption use Public key , It has to be used in pairs .

1.1.1 Symmetric encryption

• advantage ： Symmetric encryption and decryption algorithms are faster , Suitable for encrypting large amounts of data .
• shortcoming ： Because encryption and decryption use the same key , Easy to crack , A large number of keys are needed to encrypt and decrypt different messages .

1.1.2 Asymmetric encryption

• advantage ： The public key is encrypted , The private key is decrypted . Or sign with the private key , Use public key to verify signature . High safety , Private key and public key are kept separately , No public key and key transmission .
• shortcoming ： Asymmetric encryption is very performance consuming , Very, very .
  At this point, we must talk about the role of public key and private key ：

Public and private keys must appear in pairs , Both can be used for encryption , But you must use the other party to decrypt . Different scenarios use different .

• Public key encryption , Private key decryption ： Ensure ciphertext transmission , Highlight confidentiality .
• Private key encryption , Public key decryption ： Sign and verify , Ensure that the signature has not been modified , Highlight reality .