RHCE first operation

1.at Configure in 5 Hours later, , take "This is a at task" write in root Home directory at_test In file

2.crontab To configure , Every Saturday , Sunday 9 Half past six ,14 spot Remind me to go RHCE course write in root Home directory cron_test In file

3. On two Linux Upper Department chrony service ： requirement ： The first one synchronizes the time from Alibaba cloud server , The second synchronizes the time from the first

4. What is symmetric encryption , What is asymmetric encryption , What are the encryption algorithms of symmetric encryption , What encryption algorithms are needed for asymmetric encryption

Symmetric encryption It means that both encryption and decryption use the same key , The asymmetric key is a pair of keys It consists of public key and private key

Symmetric key Compared with asymmetric key encryption, it is faster , But the security is not as good as asymmetric key  , Asymmetric keys ensure a certain degree of security  , But the identity of the other party cannot be confirmed , There are also risks .

Symmetric encryption algorithm ：DES encryption 、 Information verification code 、AES encryption 、 triple ·DES

Encryption algorithm of asymmetric encryption ：RSA、Elgamal、 Knapsack algorithm 、Rabin、D-H、ECC Elliptic curve encryption algorithm