How to Generate CSR using Openssl in Linux

Before Generating CSR ,let see what is Openssl.

It is nothing but a core library ,which is used for general purpose in cryptography,it is an open source product which work towards the implementation of SSL and TLS protocols.

Talking about openssl, some people called the certificates generated from openssl as "self signed certificate".

lets go towards now,creating CSR and private key using openssl command,

Just log in to any of your Linux box and run following command as root user replacing the required information as per your need .

[root@SVR home]# openssl req -new -newkey  rsa:2048 -nodes -sha256 -out domain_name.csr -keyout domain_name.key -subj "/C=US/ST=state/L=locality/O=organization/OU=organization unit Dept/CN=www.domain.com"

 You will get output like :

Then check whether ,all the information we have entered ,while creating CSR is proper ,by decoding the CSR from some online tool.

First do the cat to the csr file

[root@SVR home]# cat domain_name.csr

-----BEGIN CERTIFICATE REQUEST-----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-----END CERTIFICATE REQUEST-----

Now, to check whether ,you have entered the proper information while creating CSR, we need to check the content of the CSR,for this refer URL

http://www.linuxforeveryone.com/2015_01_01_archive.html


And if you want self signed certificate ,then we can use below openssl command
to get a Certificate using csr and private key we have just created. 
Use below command for this purpose.


openssl x509 -signkey domain_name.key -sha256  -in domain_name.csr -req -days 365 -out domain.crt

Where,

domain_name.key ===== is  private key.
domain_name.csr ===== is csr.
-days ===== Number of days of validity ,you want for your cert.