Generate a CA certificate - Classic Load Balancer| Alibaba Cloud Documentation Center

When you configure an HTTPS listener, you can use a self-signed CA certificate. This topic describes how to generate a CA certificate and use the CA certificate to sign a client certificate.

Generate a CA certificate by using Open SSL

Run the following commands to create a ca folder in the /root directory and then create four subfolders under the ca folder.
```
 $ sudo mkdir ca
 $ cd ca
 $ sudo mkdir newcerts private conf server
```
- newcerts is used to store the digital certificate signed by the CA certificate.
- private is used to store the private key of the CA certificate.
- conf is used to store the configuration files used for simplifying parameters.
- server is used to store the server certificate.

Create an openssl.conf file that contains the following information in the conf directory.

 [ ca ]
 default_ca = foo
 [ foo ] 
 dir = /root/ca
 database = /root/ca/index.txt
 new_certs_dir = /root/ca/newcerts
 certificate = /root/ca/private/ca.crt
 serial = /root/ca/serial
 private_key = /root/ca/private/ca.key
 RANDFILE = /root/ca/private/.rand
 default_days = 365
 default_crl_days= 30
 default_md = md5
 unique_subject = no
 policy = policy_any
 [ policy_any ]
 countryName = match
 stateOrProvinceName = match
 organizationName = match
 organizationalUnitName = match
 localityName = optional
 commonName      = supplied
 emailAddress    = optional

Run the following command to generate a private key.
```
$ cd /root/ca
 $ sudo openssl genrsa -out private/ca.key
```
The following figure is an example of the key generation.
Run the following command and input the required information according to the prompts. Press Enter to generate a csr file.
```
$ sudo openssl req -new -key private/ca.key -out private/ca.csr
```
Note Common Name is the domain name of the SLB instance.

Run the following command to generate a crt file:

$ sudo openssl x509 -req -days 365 -in private/ca.csr -signkey private/ca.key -out private/ca.crt

Run the following command to set the start sequence number for the private key, which can be any four characters.
```
$ sudo echo FACE > serial
```
Run the following command to create a CA key library:
```
$ sudo touch index.txt
```

Run the following command to create a certificate revocation list for removing the client certificate:

$ sudo openssl ca -gencrl -out /root/ca/private/ca.crl -crldays 7 -config "/root/ca/conf/openssl.conf"

The output is:

Using configuration from /root/ca/conf/openssl.conf

Sign the client certificate

Run the following command to generate a users folder under the ca directory to store the client key.
```
$ sudo mkdir users
```
Run the following command to create a key for the client certificate:
```
$ sudo openssl genrsa -des3 -out /root/ca/users/client.key 1024
```
Note Enter a pass phrase when creating the key. It is the password to protect the private key from unauthorized access. Enter the same password twice.
Run the following command to create a csr file for the client key.
```
$ sudo openssl req -new -key /root/ca/users/client.key -out /root/ca/users/client.csr
```
Enter the pass phrase set in the previous step and other required information when prompted.

Note A challenge password is the password of the client certificate. Note that it is not the password of the client key.

Run the following command to sign the client key.

$ sudo openssl ca -in /root/ca/users/client.csr -cert /root/ca/private/ca.crt -keyfile /root/ca/private/ca.key -out /root/ca/users/client.crt -config "/root/ca/conf/openssl.conf"

Enter y twice when prompted to confirm the operation.

Run the following command to convert the certificate to a PKCS12 file.
```
$ sudo openssl pkcs12 -export -clcerts -in /root/ca/users/client.crt -inkey /root/ca/users/client.key -out /root/ca/users/client.p12
```
Follow the prompts to enter the pass phrase of client key. Then enter the password used for exporting the client certificate. This password is used to protect the client certificate, which is required when you install the client certificate.
Run the following commands to view the generated client certificate:
```
 cd users
 ls
```