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Digital Certificates

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Digital certificates

OpenSSL is also an excellent tool for creating Certificate Authorities and generating digital certificates. In this part we will see how we can create a Certificate Authority, generate requests for digital certificates and issue those digital certificates. On most of this commands, we are going to use the openssl.cnfarrow-up-right file. This openssl.cnf file is usually distributed with the Openssl distribution.

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Create a certification authority

To create our own Certificate Authority (CA) we will create a folder structure that contains a series of CA information.

mkdir private certs newcerts crl

Next we create two files that serve as a database for storing some of CA's supporting information:

touch index.txt

echo '01' > serial

And we will create the application for the certificate itself based on a set of characteristics:

  • We will use the OpenSSL configuration file (it will come with your OpenSSL installation)

  • The output will be generated in an X.509 structure

  • We specify what a set of extensions will contain

  • We specify where the key pair and certificate will be stored

  • We specify that the certificate will be generated for a period of 5 years (1825 days)

Use this command (parts of the command, depend on the configuration present in openssl.cnf, namely the -extensions):

And then request the necessary information:

After this, the certificate will be produced.

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Verify the generated digital certificate

We can check the generated (self-signed) digital certificate by viewing the X.509 structure.

This is the structure of the certificate:

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Generate a digital certificate request

Let's now start operating the CA as if it were a real CA. One of the important steps is that when someone tries to request a certificate from a CA they need to create a Certificate Signing Request (CSR). So we are going to create that.

In this specific case we chose not to protect the private key with a password (-nodes), which is not recommended in a production environment. On the other hand, the request will be made for one year (365 days).

Then supply the request information:

We can verify the request using the following command:

Check the request that is about to be made:

Before issuing the certificate (signing it with its own private key), a CA must check the contents of the CSR.

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Issuance of the digital certificate

This step is important because it is performed by a CA to issue a digital certificate to an entity that requests it. To generate this digital certificate, the previously generated CSR must be used.

This is the issuance process:

To confirm that the certificate was issued correctly, we can view it using the command we saw earlier:

And look at the certificate data:

This book in this linkarrow-up-right also contains detailed instructions on how to create your own private CA.

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Revocation of digital certificates

One of the functions of a CA is also to maintain information about the digital certificates it issues. Whenever a certificate, for whatever reason, is no longer valid, it must be revoked. One of the ways to revoke and communicate this revocation to "third parties" is through a Certificate Revocation List (CRL).

To revoke a certificate, using OpenSSl, we can do the following:

And the proper certificate gets revoked:

The certificate is thus revoked and to switch to the CRL the following must be done:

To view the certificates that are part of the CRL, we can do the following:

Look at the revocationlist of the CA:

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