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The Secure Sockets Layer (SSL) is a computer networking protocol that manages server authentication, client authentication and encrypted communication between servers and clients.

SSL uses a combination of public-key and symmetric-key encryption to secure a connection between two machines, typically a Web or mail server and a client machine, communicating over the Internet or an internal network.

Using the OSI reference model as context, SSL runs above the TCP/IP protocol, which is responsible for the transport and routing of data over a network, and below higher-level protocols such as HTTP and IMAP, encrypting the data of network connections in the application layer of the Internet Protocol suite. The "sockets" part of the term refers to the sockets method of passing data back and forth between a client and a server program in a network, or between program layers in the same computer.

The Transport Layer Security (TLS) protocol evolved from SSL and has largely superseded it, although the terms SSL or SSL/TLS are still commonly used; SSL is often used to refer to what is actually TLS. The combination of SSL/TLS is the most widely deployed security protocol used today and is found in applications such as Web browsers, email and basically any situation where data needs to be securely exchanged over a network, like file transfers, VPN connections, instant messaging and voice over IP.

How it works

The SSL protocol includes two sub-protocols: the record protocol and the "handshake" protocol. These protocols allow a client to authenticate a server and establish an encrypted SSL connection. In what's referred to as the "initial handshake process," a server that supports SSL presents its digital certificate to the client to authenticate the server's identity. Server certificates follow the X.509 certificate format that is defined by the Public-Key Cryptography Standards (PKCS). The authentication process uses public-key encryption to validate the digital certificate and confirm that a server is in fact the server it claims to be.

Once the server has been authenticated, the client and server establish cipher settings and a shared key to encrypt the information they exchange during the remainder of the session. This provides data confidentiality and integrity. This whole process is invisible to the user. For example, if a webpage requires an SSL connection, the URL will change from HTTP to HTTPS and a padlock icon appears in the browser once the server has been authenticated.

The handshake also allows the client to authenticate itself to the server. In this case, after server authentication is successfully completed, the client must present its certificate to the server to authenticate the client's identity before the encrypted SSL session can be established.

In practice, how is SSL used in today’s modern e-commerce enabled / online workflow and service society?

  • To secure online credit card transactions.
  • To secure system logins and any sensitive information exchanged online.
  • To secure webmail and applications like Outlook Web Access, Exchange and Office Communications Server.
  • To secure workflow and virtualization applications like Citrix Delivery Platforms or cloud-based computing platforms.
  • To secure the connection between an email client such as Microsoft Outlook and an email server such as Microsoft Exchange.
  • To secure the transfer of files over https and FTP(s) services such as website owners updating new pages to their websites or transferring large files.
  • To secure hosting control panel logins and activity like Parallels, cPanel, and others.
  • To secure intranet based traffic such as internal networks, file sharing, extranets, and database connections.
  • To secure network logins and other network traffic with SSL VPNs such as VPN Access Servers or applications like the Citrix Access Gateway.

All these applications have a number of shared themes:

  • The data being transmitted over the Internet or network needs confidentiality. In other words, people do not want their credit card number, account login,     passwords or personal information to be exposed over the Internet.
  • The data needs to remain integral, which means that once credit card details and the amount to be charged to the credit card have been sent, a hacker sitting in     the middle cannot change the amount to be charged and where the funds should go.
  • Your organization needs identity assurance to authenticate itself to customers / extranet users and ensure them they are dealing with the right organization.
  • Your organization needs to comply with regional, national or international regulations on data privacy, security and integrity.

How Does the SSL Certificate Create a Secure Connection?

When a browser attempts to access a website that is secured by SSL, the browser and the web server establish an SSL connection using a process called an “SSL Handshake” (see diagram below). Note that the SSL Handshake is invisible to the user and happens instantaneously.

Essentially, three keys are used to set up the SSL connection: the public, private, and session keys. Anything encrypted with the public key can only be decrypted with the private key, and vice versa.

Because encrypting and decrypting with private and public key takes a lot of processing power, they are only used during the SSL Handshake to create a symmetric session key. After the secure connection is made, the session key is used to encrypt all transmitted data.


  • Browser connects to a web server (website) secured with SSL (https). Browser requests that the server identify itself.
  • Server sends a copy of its SSL Certificate, including the server’s public key.
  • Browser checks the certificate root against a list of trusted CAs and that the certificate is unexpired, unrevoked, and that its common name is valid for the website that it is connecting to. If the browser trusts the certificate, it creates, encrypts, and sends back a symmetric session key using the server’s public key.
  • Server decrypts the symmetric session key using its private key and sends back an acknowledgement encrypted with the session key to start the encrypted session.
  • Server and Browser now encrypt all transmitted data with the session key.

Why Do I Need SSL?

One of the most important components of online business is creating a trusted environment where potential customers feel confident in making purchases. Browsers give visual cues, such as a lock icon or a green bar, to help visitors know when their connection is secured.