<p>Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are cryptographic protocols that provide secure communications on the Internet for web browsing, e-mail, Internet faxing, instant messaging and other data transfers. There are slight differences between SSL and TLS, but they are largely the same.</p>
<p>TLS involves three basic phases:</p>
<ol type="1" class="MadCap1">
<li class="MadCap3" value="1"> Peer negotiation for algorithm support</li>
<li class="MadCap3" value="2">Key exchange and authentication</li>
<li class="MadCap3" value="3">Symmetric cipher encryption and message authentication</li>
</ol>
<p>During the first phase, the client and server negotiate cipher suites, which determine the ciphers to be used, the key exchange and authentication algorithms, as well as the message authentication codes (MACs). The key exchange and authentication algorithms are typically public key algorithms, or as in TLS-PSK pre-shared keys could be used. The message authentication codes are made up from cryptographic hash functions using the HMAC construction.</p>
