In this article you’ll find how to generate CSR (Certificate Signing Request) using OpenSSL from the Linux command line, without being prompted for values which go in the certificate’s subject field.
For this task you can use your favorite tool to generate certificates and keys. The commands below use openssl. Create a root certificate and private key to sign the certificate for your services: $ openssl req -x509 -sha256 -nodes -days 365 -newkey rsa:2048 -subj '/O=example Inc./CN=example.com' -keyout example.com.key -out example.com.crt.
Below you’ll find two examples of creating CSR using OpenSSL.
In the first example, i’ll show how to create both CSR and the new private key in one command.
And in the second example, you’ll find how to generate CSR from the existing key (if you already have the private key and want to keep it).
To generate the missing public key again from the private key, the following command will generate the public key of the private key provided with the -f option. $ ssh-keygen -y -f /.ssh/idrsa /.ssh/idrsa.pub Enter passphrase: The -y option will read a private SSH key file and prints an SSH public key to stdout. The public key part is redirected to the file with the. Private key generate public key.
Both examples show how to create CSR using OpenSSL non-interactively (without being prompted for subject), so you can use them in any shell scripts.
Use the following command to create a new private key 2048 bits in size example.key
and generate CSR example.csr
from it:
Option | Description |
---|---|
openssl req | certificate request generating utility |
-nodes | if a private key is created it will not be encrypted |
-newkey | creates a new certificate request and a new private key |
rsa:2048 | generates an RSA key 2048 bits in size |
-keyout | the filename to write the newly created private key to |
-out | specifies the output filename |
-subj | sets certificate subject |
Use the following command to generate CSR example.csr
from the private key example.key
:
Option | Description |
---|---|
openssl req | certificate request generating utility |
-new | generates a new certificate request |
-key | specifies the file to read the private key from |
-out | specifies the output filename |
-subj | sets certificate subject |
The magic of CSR generation without being prompted for values which go in the certificate’s subject field, is in the -subj
option.
-subj arg | Replaces subject field of input request with specified data and outputs modified request. The arg must be formatted as /type0=value0/type1=value1/type2=…, characters may be escaped by (backslash), no spaces are skipped. |
The fields, required in CSR are listed below:
Field | Meaning | Example |
---|---|---|
/C= | Country | GB |
/ST= | State | London |
/L= | Location | London |
/O= | Organization | Global Security |
/OU= | Organizational Unit | IT Department |
/CN= | Common Name | example.com |
You’ve created encoded file with certificate signing request.
Now you can decode CSR to verify that it contains the correct information.