If you don't have access to a certificate authority (CA) for your organization and want to use OpenSearch for non-demo purposes, you can generate your own self-signed certificates using [OpenSSL](https://www.openssl.org/){:target='\_blank'}.
You can probably find OpenSSL in the package manager for your operating system.
On CentOS, use Yum:
```bash
sudo yum install openssl
```
On macOS, use [Homebrew](https://brew.sh/){:target='\_blank'}:
```bash
brew install openssl
```
## Generate a private key
The first step in this process is to generate a private key using the `genrsa` command. As the name suggests, you should keep this file private.
Private keys must be of sufficient length to be secure, so specify `2048`:
```bash
openssl genrsa -out root-ca-key.pem 2048
```
You can optionally add the `-aes256` option to encrypt the key using the AES-256 standard. This option requires a password.
## Generate a root certificate
Next, use the key to generate a self-signed certificate for the root CA:
Change `-days 30` to 3650 (10 years) or some other number to set a non-default expiration date. The default value of 30 days is best for testing purposes.
- The `-x509` option specifies that you want a self-signed certificate rather than a certificate request.
- The `-sha256` option sets the hash algorithm to SHA-256. SHA-256 is the default in later versions of OpenSSL, but earlier versions might use SHA-1.
Follow the prompts to specify details for your organization. Together, these details form the distinguished name (DN) of your CA.
## Generate an admin certificate
To generate an admin certificate, first create a new key:
```bash
openssl genrsa -out admin-key-temp.pem 2048
```
Then convert that key to PKCS#8 format for use in Java using a PKCS#12-compatible algorithm (3DES):
Follow the prompts to fill in the details. You don't need to specify a challenge password. As noted in the [OpenSSL Cookbook](https://www.feistyduck.com/books/openssl-cookbook/){:target='\_blank'}, "Having a challenge password does not increase the security of the CSR in any way."
Follow the steps in [Generate an admin certificate](#generate-an-admin-certificate) with new file names to generate a new certificate for each node and as many client certificates as you need. For example, you might generate one client certificate for OpenSearch Dashboards and another for a Python client. Each certificate should use its own private key.
If you generate node certificates and have `plugins.security.ssl.transport.enforce_hostname_verification` set to `true` (default), be sure to specify a common name (CN) for the certificate that matches the hostname of the intended node. If you want to use the same node certificate on all nodes (not recommended), set hostname verification to `false`. For more information, see [Configure TLS certificates]({{site.url}}{{site.baseurl}}/security-plugin/configuration/tls#advanced-hostname-verification-and-dns-lookup).
If you already know the certificate details and don't want to specify them interactively, use the `-subj` option in your `root-ca.pem` and CSR commands. This script creates a root certificate, admin certificate, two node certificates, and a client certificate, all with an expiration dates of two years (730 days):
You must specify the distinguished names (DNs) for all admin and node certificates in `opensearch.yml` on all nodes. Using the certificates from the sample script above, part of `opensearch.yml` might look like this:
If you compare this string to the ones above, you can see that you need to invert the order of elements and use commas rather than slashes. Enter this command to get the correct string:
For more information about adding and using these certificates in your own setup, see [Docker security configuration]({{site.url}}{{site.baseurl}}//opensearch/install/docker-security/), [Configure TLS certificates]({{site.url}}{{site.baseurl}}/security-plugin/configuration/tls/), and [Client certificate authentication]({{site.url}}{{site.baseurl}}/security-plugin/configuration/client-auth/).
After configuring your certificates and starting OpenSearch, run `securityadmin.sh` to initialize the security plugin. For information about how to use this script, see [Apply configuration changes]({{site.url}}{{site.baseurl}}/security-plugin/configuration/security-admin/).
For information on using your root CA and a client certificate to enable TLS for OpenSearch Dashboards, see [Configure TLS for OpenSearch Dashboards]({{site.url}}{{site.baseurl}}/dashboards/install/tls/).
