Use Openssl To Generate Private Key And Csr

  • Related Questions & Answers

Second one will have.csr extension, which is the CSR. Generate CSR from an existing Private Key. You may already have an existing key pair with you and you would like to use the same for requesting certificate. In this case, you can use below command: openssl req -key mywebsite.key -new -out mywebsite.csr.

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OpenSSL is a CLI (Command Line Tool) which can be used to secure the server to generate public key infrastructure (PKI) and HTTPS. This article helps you as a quick reference to understand OpenSSL commands which are very useful in common, and for everyday scenarios especially for system administrators.

Certificate Signing Requests (CSRs)

If we want to obtain SSL certificate from a certificate authority (CA), we must generate a certificate signing request (CSR). A CSR consists of mainly the public key of a key pair, and some additional information. Both these components are merged into the certificate whenever we are signing for the CSR.

While generating a CSR, the system will prompt for information regarding the certificate and this information is called as Distinguished Name (DN). The important field in the DN is the Common Name (CN) which should be the FQND (Fully Qualified Domain Name) of the server or the host where we intend to use the certificate with.

The next item in a DN is to provide the additional information about our business or organization. If we purchase an SSL certificate from a certificate authority (CA), it is very important and required that these additional fields like “Organization” should reflect your organization for details.

Use Openssl To Generate Private Key And Csr

Here is a general example for the CSR information prompt, when we run the OpenSSL command to generate the CSR.

We can also provide the information by non-interactive answers for the CSR information generation, we can do this by adding the –subj option to any OpenSSL commands that we try to generate or run.

Below is an example for the –subj option where we can provide the information of the organization where we want to use this CSR.

Generating CSRs

In this section, we will cover about OpenSSL commands which are related to generating the CSR. This CSR can be used to request an SSL certificate from a certificate authority.

Generate a Private Key and a CSR

If we want to use HTTPS (HTTP over TLS) to secure the Apache or Nginx web servers (using a Certificate Authority (CA) to issue the SSL certificate). Also, the ‘.CSR’ which we will be generating has to be sent to a CA for requesting the certificate for obtaining CA-signed SSL.

Below is the command to create a 2048-bit private key for ‘domain.key’ and a CSR ‘domain.csr’ from the scratch.

The ‘–newkey rsa:2048’ is the option which we are specifying that the key should be 2048-bit using the RSA algorithm. The ’ –nodes’ option is to specifying that the private key should not be encrypted with a pass phrase. The ‘-new’ option, indicates that a CSR is being generated.

Generate a CSR from an Existing Private Key

Use Openssl To Generate Private Key And Csr Free

Here we will learn about, how to generate a CSR for which you have the private key.

Below is the command to create a new .csr file based on the private key which we already have.

Generate a CSR from an Existing Certificate and Private key

Use Openssl To Generate Private Key And Csr Key

Here we can generate or renew an existing certificate where we miss the CSR file due to some reason. Here, the CSR will extract the information using the .CRT file which we have.

Use Openssl To Generate Private Key And Csr 1

Below is the example for generating –

Where -x509toreq is specified that we are using the x509 certificate files to make a CSR.

Generating a Self-Singed Certificates

Here we will generate the Certificate to secure the web server where we use the self-signed certificate to use for development and testing purpose.

Here, we generate self-signed certificate using –x509 option, we can generate certificates with a validity of 365 days using –days 365 and a temporary .CSR files are generated using the above information.

Viewing the Certificates Files

Please note that, CSR files are encoded with .PEM format (which is not readable by the humans). This is required to view a certificate. In this section, we can cover the OpenSSL commands which are encoded with .PEM files.

Viewing CSR Files Entires

The below command will be used to view the contents of the .CRT files Ex (domain.crt) in the plain text format.

Working with Private Keys

In this section, will see how to use OpenSSL commands that are specific to creating and verifying the private keys.

Public Key

Create a Private Key

Below is the command to create a password-protected and, 2048-bit encrypted private key file (ex. domain.key) –

Enter a password when prompted to complete the process.

Openssl generate csr san

Verify a Private Key

Private Key Definition

Below is the command to check that a private key which we have generated (ex: domain.key) is a valid key or not

If the private key is encrypted, you will be prompted to enter the pass phrase. Upon the successful entry, the unencrypted key will be the output on the terminal.

Symmetric Key

In this article, we have learnt some commands and usage of OpenSSL commands which deals with SSL certificates where the OpenSSL has lots of features. We will learn more features and usage in the future. I hope this article will help us to understand some basic features of the OpenSSL.