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<h1 class="topictitle1">How SSL works</h1>
<div><p>SSL is actually two protocols. The protocols are the record protocol
and the handshake protocol. The record protocol controls the flow of the data
between the two endpoints of an SSL session.</p>
<p>The handshake protocol authenticates one or both endpoints of the SSL session
and establishes a unique symmetric key used to generate keys to encrypt and
decrypt data for that SSL session. SSL uses asymmetric cryptography, digital
certificates, and SSL handshake flows, to authenticate one or both endpoints
of an SSL session. Typically, SSL authenticates the server. Optionally, SSL
authenticates the client. A digital certificate, issued by a Certificate Authority,
can be assigned to each of the endpoints or to the applications using SSL
on each endpoint of the connection. </p>
<p>The digital certificate is comprised of a public key and some identifying
information that a trusted Certificate Authority (CA) has digitally signed.
Each public key has an associated private key. The private key is not stored
with or as part of the certificate. In both server and client authentication,
the endpoint which is being authenticated must prove that it has access to
the private key associated with the public key contained within the digital
certificate. </p>
<p>SSL handshakes are performance intensive operations because of the cryptographic
operations using the public and private keys. After an initial SSL session
has been established between two endpoints, the SSL session information for
these two endpoints and applications can be cached in secure memory to speed
up subsequent SSL session enablements. When an SSL session is resumed, the
two endpoints use an abbreviated handshake flow to authenticate that each
has access to unique information without using the public or private keys.
If both can prove that they have access to this unique information, then
new symmetric keys are established and the SSL session resumes. For TLS Version
1.0 and SSL Version 3.0 sessions, cached information will not remain in the
secure memory for greater than 24 hours. In OS/400<sup>®</sup> V5R2 and subsequent releases
or i5/OS™,
you can minimize SSL handshake performance impacts on the main CPU by using
cryptographic hardware.</p>
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<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzainconcepts.htm" title="SSL concepts includes supplemental information, providing some basic building blocks for the Secure Sockets Layer (SSL) protocols.">Concepts</a></div>
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<div class="relinfo"><strong>Related information</strong><br />
<div><a href="../rzahu/rzahurzahu4abunderstanddc.htm">Digital certificate concepts</a></div>
<div><a href="../rzajc/rzajcoverview.htm">Cryptographic hardware</a></div>
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