October 18, 2013

Why do we need SSL certificates?

What is SSL/TLS?

Secure Sockets Layer (SSL) and its successor Transport Layer Security (TLS) are cryptographic protocols designed to provide secure connection between a server and a client, typically a web server and a browser or a mail server and a mail client.

SSL protocol defines the structure of the data transfered and the procedure to establish an encrypted connection, it also makes sure of the integrity of the data.

Normally, data is sent between browsers and web servers in plain text, which is vulnerable to eavesdropping. SSL allows sensitive information such as credit card numbers, user names and passwords, personal details to be transmitted securely.

SSL is used on a daily basis. Internet users recognize secure connection in browsers by a padlock icon next to the website address or a green address bar that comes with extended validation certificates. SSL secured websites also begin with https.

What is an SSL certificate

An SSL certificate consists of a public and a private key. Those two keys are used to establish a secure connection. The certificate contains information about the issuer, subject, which is the identity of the website owner, and the validity of the certificate.

Certificate Authority

SSL certificates are signed by Certificate Authority (CA), after verifying identity of an applicant. Depending on the certificate type Certificate Authority might require different forms of validation. For domain validated certificate ownership of the domain has to be proven. In case of Extended validation certificates require verification of the legal, physical and operational existence of the requesting entity, as well as it has exclusive right to use the domain.

All Internet browsers are capable of interacting with secured websites using SSL protocol. Many Certificate Authorities have their root certificates embedded in browsers so your web browser automatically trusts them. They will sign an entity’s certificate using their trusted root certificate (or an intermediate of it) to create a "chain of trust" so the browser will trust the entity’s certificate.

A Certificate Authority will need a Certificate Signing Request to sign your SSL certificate.

Certificate Signing Request

To get a certificate you need to generate a Certificate Signing Request (CSR) which contains all information that will be included in your certificate such as your organization name, domain name, locality and country. It also contains the public key that will be included in your certificate. A private key is usually created at the same time that you create the CSR.

The following command will generate a 2048-bit RSA private key with a CSR.

$ openssl req -new -newkey rsa:2048 -nodes -keyout <em>server.key</em> -out <em>server.csr</em>
...
<span class="output">Country Name (2 letter code) [AU]:</span> <em>PL</em>
<span class="output">Common Name (e.g. server FQDN or YOUR name) []:</span> <em>shellycloud.com</em>
...

Created CSR server.csr can be sent to a Certificate Authority of your choice, to sign your certificate. Make sure to keep your private key secret and safe. The certificate created with a particular CSR will only work with the private key that was generated with it. So if you lose the private key, the certificate will no longer work.

Secure connection with a SSL certificate

When a browser attempts to access a website that is secured by SSL, the browser and the web server establish a secure connection using a process called SSL Handshake. This process is responsible for specifying encryption methods and keys that will be used for the remainder of the communications. SSL Handshake is transparent to the end user and happens instantaneously.

SSL Handshake uses asymmetric cryptography as well as the symmetric cryptography. Asymmetric cryptography uses two separate keys, one public and one private. Public key is used for encryption or verification of a digital signature. Private key is used for decrypting or creating digital signature. Symmetric cryptography uses the same key for both encryption and decryption.

SSL Handshake uses your certificate's public and private key, and a session key which is generated during that process. Asymmetric cryptography takes more processing power, therefore your public and private key are used only to create a symmetric session key.

SSL Handshake

  1. Browser makes a request to a secure page with https.
  2. Web server sends its SSL Certificate, its public key.
  3. Browser ensures that the certificate is valid, was issued by a trusted Certificate Authority and that its common name is valid for the website that it is connecting to. If the browser trusts the certificate it creates a symmetric session key using server's public key and sends it back.
  4. Symmetric session key is decrypted with the private key and web server sends back an acknowledgment encrypted with the session key to start the encrypted session.
  5. Web server and browser encrypts all transmitted data with the session key.

Why you should use SSL?

One of the most important factors of creating a successful on-line business is trust of customers. One of the way to accomplish this is by securing your website with SSL Certificates, making sure that all your customer data, logins, passwords, personal information, are transmitted safely between your web server and user browsers.

Installing SSL certificates

Installing an SSL certificate will vary depending on the type of the web server. In case of Nginx web server installation will look as follows:

  1. Copy SSL certificate and key to your Nginx server
  2. Configure Nginx Server Block
    server {
      listen                    443 ssl;
      server_name               www.example.com;
      ssl_certificate           /path/to/www.example.com.crt;
      ssl_certificate_key       /path/to/www.example.com.key;
      ssl_protocols             SSLv3 TLSv1 TLSv1.1 TLSv1.2;
      ssl_ciphers               'recommended ciphersuite, see below'
      ssl_prefer_server_ciphers on;
      ssl_session_cache         shared:SSL:50m;
      ...
    }
  1. Confirm that your Nginx configuration is correct and reload your server
  # nginx -t
  nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
  nginx: configuration file /etc/nginx/nginx.conf test is successful

  # /etc/init.d/nginx reload
  [ ok ] Reloading nginx configuration: nginx.
  1. Verify your website using SSL testing suite

Recommended ciphersuite

Using the proper ciphersuite is very important. Specifying SSL protocols and used ciphers ensures that SSL attacks like CRIME, LUCKY13, BEAST are mitigated. We encourage to use Mozilla recommended cipersuite.

Shelly Cloud users

If your a Shelly Cloud user, adding an SSL certificate to your application will be as easy as issuing one command with shelly utility.


Read one of our other articles - How does our CSS architecture look like after getting rid of Bootstrap

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