How to generate an X509 public key certificate?

In a previous blog post I gave you a solution for generating a self-signed X509 certificate on Windows using the OpenSSL command line.

Now I will show you how to generate a self-signed X509 certificate on Unix/Linux using the OpenSSL command line.

The first step is to generate a RSA private key. To do so, we type the following command in the command line.key 1024

The above command generates a 2025 bit RSA key, but it can be configured to generate any bit size (512, 1024, 2025, etc). The -out option tells the OpenSSL command line tool which file to write the key and the other options are explained in the OpenSSL man page.

The next step is to create a public/private key pair.key -pubout -out public.key

The above command generates a public/private key pair, it is very important to remember that the private key stays private and should never be distributed. The public key is sent to the server.

Now we have to generate the self-signed certificate. The following command will do that:key -out cert.pem -days 3650

The above command generates a self-signed X509 certificate. The -new option requests a new certificate, the -x509 option tells the OpenSSL command line tool to use the RSA private key we just created. The -key option is used to specify the private key file we want to use and the -out option writes the certificate to cert. Finally the -days option sets the validity time of the certificate.

I hope that helped. If you want to learn more about this subject feel free to join my mailing list or to follow me on Twitter.

What is the X509 certificate format?

A certificate format is a file containing information about a certificate.

It contains the certificate's public key, the certificate's owner, and the validity period of the certificate. This is all of the data that a web browser (or any application that needs to make a secure connection) requires.

The format of the certificate file is called X.509. The most common form of X.509 certificate is PKCS#7, but other formats are also used.

How does a certificate work? A certificate can be stored in a digital file called an electronic certificate or a physical file called a paper certificate. A certificate contains information about the certificate's owner and validity.

A certificate contains a public key that is used to prove the identity of the owner. In the case of a certificate for a web server, the owner is the web server, and the validity period of the certificate is how long the certificate is valid. A web browser checks the certificate's expiration date to determine whether the certificate is still valid.

Certificate expiration is controlled by the CA that issues the certificate. In most cases, the CA sets a maximum validity period for each certificate it issues. When the certificate expires, the CA destroys the certificate and no longer trusts the certificate owner.

How do certificates work with an SSL connection? To use an SSL connection, a client program opens a socket connection to the web server and requests a web page. The client program sends the URL for the web page to the web server using HTTP GET or POST. The web server signs the request using its private key and returns the response to the client program.

In this example, the certificate from the web server is used to encrypt the response. If the certificate is valid, the server knows that the client is allowed to access the web page because the server trusts the certificate. If the certificate is not valid, the server does not know if the client is trusted or not.

The server signs the response with its private key and returns it to the client. The certificate is encrypted using the public key of the server certificate. The web browser then decrypts the certificate and uses the certificate's public key to decrypt the response. The response is sent back to the browser for the user to view.

When the certificate expires, the server certificate becomes invalid. The web browser no longer trusts the certificate and the web page will not load.

How to get an X509 digital certificate?

First, I don't know if the SSL/TLS protocol is only implemented in browsers, then it would be hard to use it in a desktop application.

Then I think that we can use OpenSSL to generate a self-signed certificate.

For Windows/Linux, OpenSSL has a simple command line example: openssl req -new -x509 -days 3650 -key privatekey.pem -out certificate.crt

Then, OpenSSL has a command line utility to generate certificates: openssl genrsa -aes256 -des3 -out privatekey.pem 2025 This creates a private key and creates a certificate request file containing the name of your domain (or any other name you wish). The key length can be 4096 or 128 (the default of the openssl genrsa command). Now we run:

Openssl req -new -key privatekey.csr And this creates an output file containing all the information required for a certificate. Now we can generate the signed certificate using a command like: openssl x509 -req -days 3650 -in certificate.csr -signkey privatekey.crt

This creates the signed version of your certificate which will be used by web browsers. So our final program does something like: OpenSSL::PKey::RSnew 2025. Certificate.new 2025 CertificateRequest.new 2025 certificatecreate( "mycertificate", # a string containing all the cert data. Self . Publickeyid )

Certificatecreate( "mycertificate", # a string containing all the cert data. Publickeyid ) certificatecreate( "mycertificate", # a string containing all the cert data.