Symmetric encryption and asymmetric encryption

1、 Symmetric encryption

Symmetric encryption , That is, symmetric cryptographic coding technology is adopted , He is characterized by , Encryption and decryption use the same secret key .

The common symmetric encryption algorithms are DES、3DES、Blowfish、IDEA、RC4、RC5、RC6 and AES.

advantage ： Symmetric encryption algorithm is easy to use , The key is shorter , And it's hard to decipher .
shortcoming ：
1、 Symmetric encryption algorithms generally can not provide authentication of information integrity . It cannot verify the identity of the sender and receiver ;
2、 The management and distribution of symmetric keys is a potentially dangerous and cumbersome process . How to prevent secret key leakage is a difficulty .

2、 Asymmetric encryption

Asymmetric encryption , You need two keys , Public and private keys . Public key and private key appear in pairs .

usage ： If you encrypt data with a public key , Only the corresponding private key can be used to decrypt ; If you encrypt data with a private key , Then only the corresponding public key can be decrypted . Because encryption and decryption use two different keys , So this algorithm is called asymmetric encryption algorithm .

The typical application of asymmetric encryption is digital signature .

The common asymmetric encryption algorithms are ：RSA、ECC（ For mobile devices ）、Diffie-Hellman、El Gamal、DSA（ For digital signature ）.

3、 symmetry + Asymmetric

1、 The sender

1、 The original message uses symmetric encryption technology . The secret key of symmetric encryption （ Avoid confusion , Here it is called symmetric password ）. Generate from random numbers . Every time a request is made , Will regenerate a random number , Further reduce the risk of being cracked .

2、 Symmetric passwords are encrypted by asymmetric encryption . The public key is generated in the background , The matching private key is kept in the background . This produces an encrypted symmetric password . The front end sends it to the back end , The back end needs a matching private key to unlock .

2、 The receiving party

1、 The encrypted symmetric password will be decrypted with the matching private key , Get the real symmetric password .

2、 Use symmetric passwords , Decrypt encrypted message , Get the content of the original message .

advantage ：
1、 Because our symmetric password uses asymmetric encryption , therefore , Want to crack , You need to find the corresponding public key .
2、 Each request will regenerate a symmetric password , This increases the difficulty of cracking .

4、 summary

（1） Symmetric encryption uses the same key as decryption , So fast , But because of the need to transfer the key over the network , So the security is not high .
（2） Asymmetric encryption uses a pair of keys , Public and private keys , So it's safe , But encryption and decryption are slow .
（3） The solution is to encrypt the symmetric encryption key with the asymmetric encryption public key , And send it out , The receiver uses the private key to decrypt to get the symmetric encryption key , Then both sides can use symmetric encryption to communicate .