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+            
+  <div class="section" id="encryption-library">
+<h1>Encryption Library<a class="headerlink" href="#encryption-library" title="Permalink to this headline">¶</a></h1>
+<div class="admonition important">
+<p class="first admonition-title">Important</p>
+<p class="last">DO NOT use this or any other <em>encryption</em> library for
+user password storage! Passwords must be <em>hashed</em> instead, and you
+should do that via PHP’s own <a class="reference external" href="http://php.net/password">Password Hashing extension</a>.</p>
+</div>
+<p>The Encryption Library provides two-way data encryption. To do so in
+a cryptographically secure way, it utilizes PHP extensions that are
+unfortunately not always available on all systems.
+You must meet one of the following dependencies in order to use this
+library:</p>
+<ul class="simple">
+<li><a class="reference external" href="http://php.net/openssl">OpenSSL</a></li>
+<li><a class="reference external" href="http://php.net/mcrypt">MCrypt</a> (and <cite>MCRYPT_DEV_URANDOM</cite> availability)</li>
+</ul>
+<p>If neither of the above dependencies is met, we simply cannot offer
+you a good enough implementation to meet the high standards required
+for proper cryptography.</p>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#using-the-encryption-library" id="id2">Using the Encryption Library</a><ul>
+<li><a class="reference internal" href="#initializing-the-class" id="id3">Initializing the Class</a></li>
+<li><a class="reference internal" href="#default-behavior" id="id4">Default behavior</a></li>
+<li><a class="reference internal" href="#setting-your-encryption-key" id="id5">Setting your encryption_key</a></li>
+<li><a class="reference internal" href="#supported-encryption-ciphers-and-modes" id="id6">Supported encryption ciphers and modes</a><ul>
+<li><a class="reference internal" href="#portable-ciphers" id="id7">Portable ciphers</a></li>
+<li><a class="reference internal" href="#driver-specific-ciphers" id="id8">Driver-specific ciphers</a></li>
+<li><a class="reference internal" href="#encryption-modes" id="id9">Encryption modes</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#message-length" id="id10">Message Length</a></li>
+<li><a class="reference internal" href="#configuring-the-library" id="id11">Configuring the library</a></li>
+<li><a class="reference internal" href="#encrypting-and-decrypting-data" id="id12">Encrypting and decrypting data</a><ul>
+<li><a class="reference internal" href="#how-it-works" id="id13">How it works</a></li>
+<li><a class="reference internal" href="#using-custom-parameters" id="id14">Using custom parameters</a></li>
+<li><a class="reference internal" href="#supported-hmac-authentication-algorithms" id="id15">Supported HMAC authentication algorithms</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#class-reference" id="id16">Class Reference</a></li>
+</ul>
+</div>
+<div class="custom-index container"></div><div class="section" id="using-the-encryption-library">
+<h2><a class="toc-backref" href="#id2">Using the Encryption Library</a><a class="headerlink" href="#using-the-encryption-library" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="initializing-the-class">
+<h3><a class="toc-backref" href="#id3">Initializing the Class</a><a class="headerlink" href="#initializing-the-class" title="Permalink to this headline">¶</a></h3>
+<p>Like most other classes in CodeIgniter, the Encryption library is
+initialized in your controller using the <code class="docutils literal"><span class="pre">$this-&gt;load-&gt;library()</span></code>
+method:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-&gt;</span><span class="na">load</span><span class="o">-&gt;</span><span class="na">library</span><span class="p">(</span><span class="s1">&#39;encryption&#39;</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Once loaded, the Encryption library object will be available using:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="default-behavior">
+<h3><a class="toc-backref" href="#id4">Default behavior</a><a class="headerlink" href="#default-behavior" title="Permalink to this headline">¶</a></h3>
+<p>By default, the Encryption Library will use the AES-128 cipher in CBC
+mode, using your configured <em>encryption_key</em> and SHA512 HMAC authentication.</p>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">AES-128 is chosen both because it is proven to be strong and
+because of its wide availability across different cryptographic
+software and programming languages’ APIs.</p>
+</div>
+<p>However, the <em>encryption_key</em> is not used as is.</p>
+<p>If you are somewhat familiar with cryptography, you should already know
+that a HMAC also requires a secret key and using the same key for both
+encryption and authentication is a bad practice.</p>
+<p>Because of that, two separate keys are derived from your already configured
+<em>encryption_key</em>: one for encryption and one for authentication. This is
+done via a technique called <a class="reference external" href="http://en.wikipedia.org/wiki/HKDF">HMAC-based Key Derivation Function</a> (HKDF).</p>
+</div>
+<div class="section" id="setting-your-encryption-key">
+<h3><a class="toc-backref" href="#id5">Setting your encryption_key</a><a class="headerlink" href="#setting-your-encryption-key" title="Permalink to this headline">¶</a></h3>
+<p>An <em>encryption key</em> is a piece of information that controls the
+cryptographic process and permits a plain-text string to be encrypted,
+and afterwards - decrypted. It is the secret “ingredient” in the whole
+process that allows you to be the only one who is able to decrypt data
+that you’ve decided to hide from the eyes of the public.
+After one key is used to encrypt data, that same key provides the <strong>only</strong>
+means to decrypt it, so not only must you chose one carefully, but you
+must not lose it or you will also lose access to the data.</p>
+<p>It must be noted that to ensure maximum security, such key <em>should</em> not
+only be as strong as possible, but also often changed. Such behavior
+however is rarely practical or possible to implement, and that is why
+CodeIgniter gives you the ability to configure a single key that is to be
+used (almost) every time.</p>
+<p>It goes without saying that you should guard your key carefully. Should
+someone gain access to your key, the data will be easily decrypted. If
+your server is not totally under your control it’s impossible to ensure
+key security so you may want to think carefully before using it for
+anything that requires high security, like storing credit card numbers.</p>
+<p>Your encryption key <strong>must</strong> be as long as the encyption algorithm in use
+allows. For AES-128, that’s 128 bits or 16 bytes (charcters) long.
+You will find a table below that shows the supported key lengths of
+different ciphers.</p>
+<p>The key should be as random as possible and it <strong>must not</strong> be a regular
+text string, nor the output of a hashing function, etc. In order to create
+a proper key, you must use the Encryption library’s <code class="docutils literal"><span class="pre">create_key()</span></code> method</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// $key will be assigned a 16-byte (128-bit) random key</span>
+<span class="nv">$key</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">create_key</span><span class="p">(</span><span class="mi">16</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>The key can be either stored in your <em>application/config/config.php</em>, or
+you can design your own storage mechanism and pass the key dynamically
+when encrypting/decrypting.</p>
+<p>To save your key to your <em>application/config/config.php</em>, open the file
+and set:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$config</span><span class="p">[</span><span class="s1">&#39;encryption_key&#39;</span><span class="p">]</span> <span class="o">=</span> <span class="s1">&#39;YOUR KEY&#39;</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>You’ll notice that the <code class="docutils literal"><span class="pre">create_key()</span></code> method outputs binary data, which
+is hard to deal with (i.e. a copy-paste may damage it), so you may use
+<code class="docutils literal"><span class="pre">bin2hex()</span></code>, <code class="docutils literal"><span class="pre">hex2bin()</span></code> or Base64-encoding to work with the key in
+a more friendly manner. For example:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// Get a hex-encoded representation of the key:</span>
+<span class="nv">$key</span> <span class="o">=</span> <span class="nb">bin2hex</span><span class="p">(</span><span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">create_key</span><span class="p">(</span><span class="mi">16</span><span class="p">));</span>
+
+<span class="c1">// Put the same value in your config with hex2bin(),</span>
+<span class="c1">// so that it is still passed as binary to the library:</span>
+<span class="nv">$config</span><span class="p">[</span><span class="s1">&#39;encryption_key&#39;</span><span class="p">]</span> <span class="o">=</span> <span class="nb">hex2bin</span><span class="p">(</span><span class="o">&lt;</span><span class="nx">your</span> <span class="nx">hex</span><span class="o">-</span><span class="nx">encoded</span> <span class="nb">key</span><span class="o">&gt;</span><span class="p">);</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="supported-encryption-ciphers-and-modes">
+<span id="ciphers-and-modes"></span><h3><a class="toc-backref" href="#id6">Supported encryption ciphers and modes</a><a class="headerlink" href="#supported-encryption-ciphers-and-modes" title="Permalink to this headline">¶</a></h3>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">The terms ‘cipher’ and ‘encryption algorithm’ are interchangeable.</p>
+</div>
+<div class="section" id="portable-ciphers">
+<h4><a class="toc-backref" href="#id7">Portable ciphers</a><a class="headerlink" href="#portable-ciphers" title="Permalink to this headline">¶</a></h4>
+<p>Because MCrypt and OpenSSL (also called drivers throughout this document)
+each support different sets of encryption algorithms and often implement
+them in different ways, our Encryption library is designed to use them in
+a portable fashion, or in other words - it enables you to use them
+interchangeably, at least for the ciphers supported by both drivers.</p>
+<p>It is also implemented in a way that aims to match the standard
+implementations in other programming languages and libraries.</p>
+<p>Here’s a list of the so called “portable” ciphers, where
+“CodeIgniter name” is the string value that you’d have to pass to the
+Encryption library to use that cipher:</p>
+<table border="1" class="docutils">
+<colgroup>
+<col width="24%" />
+<col width="18%" />
+<col width="28%" />
+<col width="31%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">Cipher name</th>
+<th class="head">CodeIgniter name</th>
+<th class="head">Key lengths (bits / bytes)</th>
+<th class="head">Supported modes</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>AES-128 / Rijndael-128</td>
+<td>aes-128</td>
+<td>128 / 16</td>
+<td>CBC, CTR, CFB, CFB8, OFB, ECB</td>
+</tr>
+<tr class="row-odd"><td>AES-192</td>
+<td>aes-192</td>
+<td>192 / 24</td>
+<td>CBC, CTR, CFB, CFB8, OFB, ECB</td>
+</tr>
+<tr class="row-even"><td>AES-256</td>
+<td>aes-256</td>
+<td>256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, ECB</td>
+</tr>
+<tr class="row-odd"><td>DES</td>
+<td>des</td>
+<td>56 / 7</td>
+<td>CBC, CFB, CFB8, OFB, ECB</td>
+</tr>
+<tr class="row-even"><td>TripleDES</td>
+<td>tripledes</td>
+<td>56 / 7, 112 / 14, 168 / 21</td>
+<td>CBC, CFB, CFB8, OFB</td>
+</tr>
+<tr class="row-odd"><td>Blowfish</td>
+<td>blowfish</td>
+<td>128-448 / 16-56</td>
+<td>CBC, CFB, OFB, ECB</td>
+</tr>
+<tr class="row-even"><td>CAST5 / CAST-128</td>
+<td>cast5</td>
+<td>88-128 / 11-16</td>
+<td>CBC, CFB, OFB, ECB</td>
+</tr>
+<tr class="row-odd"><td>RC4 / ARCFour</td>
+<td>rc4</td>
+<td>40-2048 / 5-256</td>
+<td>Stream</td>
+</tr>
+</tbody>
+</table>
+<div class="admonition important">
+<p class="first admonition-title">Important</p>
+<p class="last">Because of how MCrypt works, if you fail to provide a key
+with the appropriate length, you might end up using a different
+algorithm than the one configured, so be really careful with that!</p>
+</div>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">In case it isn’t clear from the above table, Blowfish, CAST5
+and RC4 support variable length keys. That is, any number in the
+shown ranges is valid, although in bit terms that only happens
+in 8-bit increments.</p>
+</div>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">Even though CAST5 supports key lengths lower than 128 bits
+(16 bytes), in fact they will just be zero-padded to the
+maximum length, as specified in <a class="reference external" href="http://tools.ietf.org/rfc/rfc2144.txt">RFC 2144</a>.</p>
+</div>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">Blowfish supports key lengths as small as 32 bits (4 bytes), but
+our tests have shown that only lengths of 128 bits (16 bytes) or
+higher are properly supported by both MCrypt and OpenSSL. It is
+also a bad practice to use such low-length keys anyway.</p>
+</div>
+</div>
+<div class="section" id="driver-specific-ciphers">
+<h4><a class="toc-backref" href="#id8">Driver-specific ciphers</a><a class="headerlink" href="#driver-specific-ciphers" title="Permalink to this headline">¶</a></h4>
+<p>As noted above, MCrypt and OpenSSL support different sets of encryption
+ciphers. For portability reasons and because we haven’t tested them
+properly, we do not advise you to use the ones that are driver-specific,
+but regardless, here’s a list of most of them:</p>
+<table border="1" class="docutils">
+<colgroup>
+<col width="15%" />
+<col width="10%" />
+<col width="32%" />
+<col width="44%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">Cipher name</th>
+<th class="head">Driver</th>
+<th class="head">Key lengths (bits / bytes)</th>
+<th class="head">Supported modes</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>AES-128</td>
+<td>OpenSSL</td>
+<td>128 / 16</td>
+<td>CBC, CTR, CFB, CFB8, OFB, ECB, XTS</td>
+</tr>
+<tr class="row-odd"><td>AES-192</td>
+<td>OpenSSL</td>
+<td>192 / 24</td>
+<td>CBC, CTR, CFB, CFB8, OFB, ECB, XTS</td>
+</tr>
+<tr class="row-even"><td>AES-256</td>
+<td>OpenSSL</td>
+<td>256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, ECB, XTS</td>
+</tr>
+<tr class="row-odd"><td>Rijndael-128</td>
+<td>MCrypt</td>
+<td>128 / 16, 192 / 24, 256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-even"><td>Rijndael-192</td>
+<td>MCrypt</td>
+<td>128 / 16, 192 / 24, 256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-odd"><td>Rijndael-256</td>
+<td>MCrypt</td>
+<td>128 / 16, 192 / 24, 256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-even"><td>GOST</td>
+<td>MCrypt</td>
+<td>256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-odd"><td>Twofish</td>
+<td>MCrypt</td>
+<td>128 / 16, 192 / 24, 256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-even"><td>CAST-128</td>
+<td>MCrypt</td>
+<td>40-128 / 5-16</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-odd"><td>CAST-256</td>
+<td>MCrypt</td>
+<td>128 / 16, 192 / 24, 256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-even"><td>Loki97</td>
+<td>MCrypt</td>
+<td>128 / 16, 192 / 24, 256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-odd"><td>SaferPlus</td>
+<td>MCrypt</td>
+<td>128 / 16, 192 / 24, 256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-even"><td>Serpent</td>
+<td>MCrypt</td>
+<td>128 / 16, 192 / 24, 256 / 32</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-odd"><td>XTEA</td>
+<td>MCrypt</td>
+<td>128 / 16</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-even"><td>RC2</td>
+<td>MCrypt</td>
+<td>8-1024 / 1-128</td>
+<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
+</tr>
+<tr class="row-odd"><td>RC2</td>
+<td>OpenSSL</td>
+<td>8-1024 / 1-128</td>
+<td>CBC, CFB, OFB, ECB</td>
+</tr>
+<tr class="row-even"><td>Camellia-128</td>
+<td>OpenSSL</td>
+<td>128 / 16</td>
+<td>CBC, CFB, CFB8, OFB, ECB</td>
+</tr>
+<tr class="row-odd"><td>Camellia-192</td>
+<td>OpenSSL</td>
+<td>192 / 24</td>
+<td>CBC, CFB, CFB8, OFB, ECB</td>
+</tr>
+<tr class="row-even"><td>Camellia-256</td>
+<td>OpenSSL</td>
+<td>256 / 32</td>
+<td>CBC, CFB, CFB8, OFB, ECB</td>
+</tr>
+<tr class="row-odd"><td>Seed</td>
+<td>OpenSSL</td>
+<td>128 / 16</td>
+<td>CBC, CFB, OFB, ECB</td>
+</tr>
+</tbody>
+</table>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">If you wish to use one of those ciphers, you’d have to pass
+its name in lower-case to the Encryption library.</p>
+</div>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">You’ve probably noticed that all AES cipers (and Rijndael-128)
+are also listed in the portable ciphers list. This is because
+drivers support different modes for these ciphers. Also, it is
+important to note that AES-128 and Rijndael-128 are actually
+the same cipher, but <strong>only</strong> when used with a 128-bit key.</p>
+</div>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">CAST-128 / CAST-5 is also listed in both the portable and
+driver-specific ciphers list. This is because OpenSSL’s
+implementation doesn’t appear to be working correctly with
+key sizes of 80 bits and lower.</p>
+</div>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">RC2 is listed as supported by both MCrypt and OpenSSL.
+However, both drivers implement them differently and they
+are not portable. It is probably worth noting that we only
+found one obscure source confirming that it is MCrypt that
+is not properly implementing it.</p>
+</div>
+</div>
+<div class="section" id="encryption-modes">
+<span id="id1"></span><h4><a class="toc-backref" href="#id9">Encryption modes</a><a class="headerlink" href="#encryption-modes" title="Permalink to this headline">¶</a></h4>
+<p>Different modes of encryption have different characteristics and serve
+for different purposes. Some are stronger than others, some are faster
+and some offer extra features.
+We are not going in depth into that here, we’ll leave that to the
+cryptography experts. The table below is to provide brief informational
+reference to our more experienced users. If you are a beginner, just
+stick to the CBC mode - it is widely accepted as strong and secure for
+general purposes.</p>
+<table border="1" class="docutils">
+<colgroup>
+<col width="6%" />
+<col width="9%" />
+<col width="9%" />
+<col width="76%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">Mode name</th>
+<th class="head">CodeIgniter name</th>
+<th class="head">Driver support</th>
+<th class="head">Additional info</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>CBC</td>
+<td>cbc</td>
+<td>MCrypt, OpenSSL</td>
+<td>A safe default choice</td>
+</tr>
+<tr class="row-odd"><td>CTR</td>
+<td>ctr</td>
+<td>MCrypt, OpenSSL</td>
+<td>Considered as theoretically better than CBC, but not as widely available</td>
+</tr>
+<tr class="row-even"><td>CFB</td>
+<td>cfb</td>
+<td>MCrypt, OpenSSL</td>
+<td>N/A</td>
+</tr>
+<tr class="row-odd"><td>CFB8</td>
+<td>cfb8</td>
+<td>MCrypt, OpenSSL</td>
+<td>Same as CFB, but operates in 8-bit mode (not recommended).</td>
+</tr>
+<tr class="row-even"><td>OFB</td>
+<td>ofb</td>
+<td>MCrypt, OpenSSL</td>
+<td>N/A</td>
+</tr>
+<tr class="row-odd"><td>OFB8</td>
+<td>ofb8</td>
+<td>MCrypt</td>
+<td>Same as OFB, but operates in 8-bit mode (not recommended).</td>
+</tr>
+<tr class="row-even"><td>ECB</td>
+<td>ecb</td>
+<td>MCrypt, OpenSSL</td>
+<td>Ignores IV (not recommended).</td>
+</tr>
+<tr class="row-odd"><td>XTS</td>
+<td>xts</td>
+<td>OpenSSL</td>
+<td>Usually used for encrypting random access data such as RAM or hard-disk storage.</td>
+</tr>
+<tr class="row-even"><td>Stream</td>
+<td>stream</td>
+<td>MCrypt, OpenSSL</td>
+<td>This is not actually a mode, it just says that a stream cipher is being used. Required because of the general cipher+mode initialization process.</td>
+</tr>
+</tbody>
+</table>
+</div>
+</div>
+<div class="section" id="message-length">
+<h3><a class="toc-backref" href="#id10">Message Length</a><a class="headerlink" href="#message-length" title="Permalink to this headline">¶</a></h3>
+<p>It’s probably important for you to know that an encrypted string is usually
+longer than the original, plain-text string (depending on the cipher).</p>
+<p>This is influenced by the cipher algorithm itself, the IV prepended to the
+cipher-text and the HMAC authentication message that is also prepended.
+Furthermore, the encrypted message is also Base64-encoded so that it is safe
+for storage and transmission, regardless of a possible character set in use.</p>
+<p>Keep this information in mind when selecting your data storage mechanism.
+Cookies, for example, can only hold 4K of information.</p>
+</div>
+<div class="section" id="configuring-the-library">
+<span id="configuration"></span><h3><a class="toc-backref" href="#id11">Configuring the library</a><a class="headerlink" href="#configuring-the-library" title="Permalink to this headline">¶</a></h3>
+<p>For usability, performance, but also historical reasons tied to our old
+<a class="reference internal" href="encrypt.html"><span class="doc">Encrypt Class</span></a>, the Encryption library is designed to
+use repeatedly the same driver, encryption cipher, mode and key.</p>
+<p>As noted in the “Default behavior” section above, this means using an
+auto-detected driver (OpenSSL has a higher priority), the AES-128 ciper
+in CBC mode, and your <code class="docutils literal"><span class="pre">$config['encryption_key']</span></code> value.</p>
+<p>If you wish to change that however, you need to use the <code class="docutils literal"><span class="pre">initialize()</span></code>
+method. It accepts an associative array of parameters, all of which are
+optional:</p>
+<table border="1" class="docutils">
+<colgroup>
+<col width="15%" />
+<col width="85%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">Option</th>
+<th class="head">Possible values</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>driver</td>
+<td>‘mcrypt’, ‘openssl’</td>
+</tr>
+<tr class="row-odd"><td>cipher</td>
+<td>Cipher name (see <a class="reference internal" href="#ciphers-and-modes"><span class="std std-ref">Supported encryption ciphers and modes</span></a>)</td>
+</tr>
+<tr class="row-even"><td>mode</td>
+<td>Encryption mode (see <a class="reference internal" href="#encryption-modes"><span class="std std-ref">Encryption modes</span></a>)</td>
+</tr>
+<tr class="row-odd"><td>key</td>
+<td>Encryption key</td>
+</tr>
+</tbody>
+</table>
+<p>For example, if you were to change the encryption algorithm and
+mode to AES-256 in CTR mode, this is what you should do:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">initialize</span><span class="p">(</span>
+        <span class="k">array</span><span class="p">(</span>
+                <span class="s1">&#39;cipher&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;aes-256&#39;</span><span class="p">,</span>
+                <span class="s1">&#39;mode&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;ctr&#39;</span><span class="p">,</span>
+                <span class="s1">&#39;key&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;&lt;a 32-character random string&gt;&#39;</span>
+        <span class="p">)</span>
+<span class="p">);</span>
+</pre></div>
+</div>
+<p>Note that we only mentioned that you want to change the ciper and mode,
+but we also included a key in the example. As previously noted, it is
+important that you choose a key with a proper size for the used algorithm.</p>
+<p>There’s also the ability to change the driver, if for some reason you
+have both, but want to use MCrypt instead of OpenSSL:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// Switch to the MCrypt driver</span>
+<span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">initialize</span><span class="p">(</span><span class="k">array</span><span class="p">(</span><span class="s1">&#39;driver&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;mcrypt&#39;</span><span class="p">));</span>
+
+<span class="c1">// Switch back to the OpenSSL driver</span>
+<span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">initialize</span><span class="p">(</span><span class="k">array</span><span class="p">(</span><span class="s1">&#39;driver&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;openssl&#39;</span><span class="p">));</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="encrypting-and-decrypting-data">
+<h3><a class="toc-backref" href="#id12">Encrypting and decrypting data</a><a class="headerlink" href="#encrypting-and-decrypting-data" title="Permalink to this headline">¶</a></h3>
+<p>Encrypting and decrypting data with the already configured library
+settings is simple. As simple as just passing the string to the
+<code class="docutils literal"><span class="pre">encrypt()</span></code> and/or <code class="docutils literal"><span class="pre">decrypt()</span></code> methods:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$plain_text</span> <span class="o">=</span> <span class="s1">&#39;This is a plain-text message!&#39;</span><span class="p">;</span>
+<span class="nv">$ciphertext</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">encrypt</span><span class="p">(</span><span class="nv">$plain_text</span><span class="p">);</span>
+
+<span class="c1">// Outputs: This is a plain-text message!</span>
+<span class="k">echo</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">decrypt</span><span class="p">(</span><span class="nv">$ciphertext</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>And that’s it! The Encryption library will do everything necessary
+for the whole process to be cryptographically secure out-of-the-box.
+You don’t need to worry about it.</p>
+<div class="admonition important">
+<p class="first admonition-title">Important</p>
+<p class="last">Both methods will return FALSE in case of an error.
+While for <code class="docutils literal"><span class="pre">encrypt()</span></code> this can only mean incorrect
+configuration, you should always check the return value
+of <code class="docutils literal"><span class="pre">decrypt()</span></code> in production code.</p>
+</div>
+<div class="section" id="how-it-works">
+<h4><a class="toc-backref" href="#id13">How it works</a><a class="headerlink" href="#how-it-works" title="Permalink to this headline">¶</a></h4>
+<p>If you must know how the process works, here’s what happens under
+the hood:</p>
+<ul class="simple">
+<li><code class="docutils literal"><span class="pre">$this-&gt;encryption-&gt;encrypt($plain_text)</span></code><ol class="arabic">
+<li>Derive an encryption key and a HMAC key from your configured
+<em>encryption_key</em> via HKDF, using the SHA-512 digest algorithm.</li>
+<li>Generate a random initialization vector (IV).</li>
+<li>Encrypt the data via AES-128 in CBC mode (or another previously
+configured cipher and mode), using the above-mentioned derived
+encryption key and IV.</li>
+<li>Prepend said IV to the resulting cipher-text.</li>
+<li>Base64-encode the resulting string, so that it can be safely
+stored or transferred without worrying about character sets.</li>
+<li>Create a SHA-512 HMAC authentication message using the derived
+HMAC key to ensure data integrity and prepend it to the Base64
+string.</li>
+</ol>
+</li>
+<li><code class="docutils literal"><span class="pre">$this-&gt;encryption-&gt;decrypt($ciphertext)</span></code><ol class="arabic">
+<li>Derive an encryption key and a HMAC key from your configured
+<em>encryption_key</em> via HKDF, using the SHA-512 digest algorithm.
+Because your configured <em>encryption_key</em> is the same, this
+will produce the same result as in the <code class="docutils literal"><span class="pre">encrypt()</span></code> method
+above - otherwise you won’t be able to decrypt it.</li>
+<li>Check if the string is long enough, separate the HMAC out of
+it and validate if it is correct (this is done in a way that
+prevents timing attacks against it). Return FALSE if either of
+the checks fails.</li>
+<li>Base64-decode the string.</li>
+<li>Separate the IV out of the cipher-text and decrypt the said
+cipher-text using that IV and the derived encryption key.</li>
+</ol>
+</li>
+</ul>
+</div>
+<div class="section" id="using-custom-parameters">
+<span id="custom-parameters"></span><h4><a class="toc-backref" href="#id14">Using custom parameters</a><a class="headerlink" href="#using-custom-parameters" title="Permalink to this headline">¶</a></h4>
+<p>Let’s say you have to interact with another system that is out
+of your control and uses another method to encrypt data. A
+method that will most certainly not match the above-described
+sequence and probably not use all of the steps either.</p>
+<p>The Encryption library allows you to change how its encryption
+and decryption processes work, so that you can easily tailor a
+custom solution for such situations.</p>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">It is possible to use the library in this way, without
+setting an <em>encryption_key</em> in your configuration file.</p>
+</div>
+<p>All you have to do is to pass an associative array with a few
+parameters to either the <code class="docutils literal"><span class="pre">encrypt()</span></code> or <code class="docutils literal"><span class="pre">decrypt()</span></code> method.
+Here’s an example:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// Assume that we have $ciphertext, $key and $hmac_key</span>
+<span class="c1">// from on outside source</span>
+
+<span class="nv">$message</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">decrypt</span><span class="p">(</span>
+        <span class="nv">$ciphertext</span><span class="p">,</span>
+        <span class="k">array</span><span class="p">(</span>
+                <span class="s1">&#39;cipher&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;blowfish&#39;</span><span class="p">,</span>
+                <span class="s1">&#39;mode&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;cbc&#39;</span><span class="p">,</span>
+                <span class="s1">&#39;key&#39;</span> <span class="o">=&gt;</span> <span class="nv">$key</span><span class="p">,</span>
+                <span class="s1">&#39;hmac_digest&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;sha256&#39;</span><span class="p">,</span>
+                <span class="s1">&#39;hmac_key&#39;</span> <span class="o">=&gt;</span> <span class="nv">$hmac_key</span>
+        <span class="p">)</span>
+<span class="p">);</span>
+</pre></div>
+</div>
+<p>In the above example, we are decrypting a message that was encrypted
+using the Blowfish cipher in CBC mode and authenticated via a SHA-256
+HMAC.</p>
+<div class="admonition important">
+<p class="first admonition-title">Important</p>
+<p class="last">Note that both ‘key’ and ‘hmac_key’ are used in this
+example. When using custom parameters, encryption and HMAC keys
+are not derived like the default behavior of the library is.</p>
+</div>
+<p>Below is a list of the available options.</p>
+<p>However, unless you really need to and you know what you are doing,
+we advise you to not change the encryption process as this could
+impact security, so please do so with caution.</p>
+<table border="1" class="docutils">
+<colgroup>
+<col width="12%" />
+<col width="14%" />
+<col width="26%" />
+<col width="49%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">Option</th>
+<th class="head">Default value</th>
+<th class="head">Mandatory / Optional</th>
+<th class="head">Description</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>cipher</td>
+<td>N/A</td>
+<td>Yes</td>
+<td>Encryption algorithm (see <a class="reference internal" href="#ciphers-and-modes"><span class="std std-ref">Supported encryption ciphers and modes</span></a>).</td>
+</tr>
+<tr class="row-odd"><td>mode</td>
+<td>N/A</td>
+<td>Yes</td>
+<td>Encryption mode (see <a class="reference internal" href="#encryption-modes"><span class="std std-ref">Encryption modes</span></a>).</td>
+</tr>
+<tr class="row-even"><td>key</td>
+<td>N/A</td>
+<td>Yes</td>
+<td>Encryption key.</td>
+</tr>
+<tr class="row-odd"><td>hmac</td>
+<td>TRUE</td>
+<td>No</td>
+<td>Whether to use a HMAC.
+Boolean. If set to FALSE, then <em>hmac_digest</em> and
+<em>hmac_key</em> will be ignored.</td>
+</tr>
+<tr class="row-even"><td>hmac_digest</td>
+<td>sha512</td>
+<td>No</td>
+<td>HMAC message digest algorithm (see <a class="reference internal" href="#digests"><span class="std std-ref">Supported HMAC authentication algorithms</span></a>).</td>
+</tr>
+<tr class="row-odd"><td>hmac_key</td>
+<td>N/A</td>
+<td>Yes, unless <em>hmac</em> is FALSE</td>
+<td>HMAC key.</td>
+</tr>
+<tr class="row-even"><td>raw_data</td>
+<td>FALSE</td>
+<td>No</td>
+<td>Whether the cipher-text should be raw.
+Boolean. If set to TRUE, then Base64 encoding and
+decoding will not be performed and HMAC will not
+be a hexadecimal string.</td>
+</tr>
+</tbody>
+</table>
+<div class="admonition important">
+<p class="first admonition-title">Important</p>
+<p class="last"><code class="docutils literal"><span class="pre">encrypt()</span></code> and <code class="docutils literal"><span class="pre">decrypt()</span></code> will return FALSE if
+a mandatory parameter is not provided or if a provided
+value is incorrect. This includes <em>hmac_key</em>, unless <em>hmac</em>
+is set to FALSE.</p>
+</div>
+</div>
+<div class="section" id="supported-hmac-authentication-algorithms">
+<span id="digests"></span><h4><a class="toc-backref" href="#id15">Supported HMAC authentication algorithms</a><a class="headerlink" href="#supported-hmac-authentication-algorithms" title="Permalink to this headline">¶</a></h4>
+<p>For HMAC message authentication, the Encryption library supports
+usage of the SHA-2 family of algorithms:</p>
+<table border="1" class="docutils">
+<colgroup>
+<col width="19%" />
+<col width="34%" />
+<col width="47%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">Algorithm</th>
+<th class="head">Raw length (bytes)</th>
+<th class="head">Hex-encoded length (bytes)</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>sha512</td>
+<td>64</td>
+<td>128</td>
+</tr>
+<tr class="row-odd"><td>sha384</td>
+<td>48</td>
+<td>96</td>
+</tr>
+<tr class="row-even"><td>sha256</td>
+<td>32</td>
+<td>64</td>
+</tr>
+<tr class="row-odd"><td>sha224</td>
+<td>28</td>
+<td>56</td>
+</tr>
+</tbody>
+</table>
+<p>The reason for not including other popular algorithms, such as
+MD5 or SHA1 is that they are no longer considered secure enough
+and as such, we don’t want to encourage their usage.
+If you absolutely need to use them, it is easy to do so via PHP’s
+native <a class="reference external" href="http://php.net/manual/en/function.hash-hmac.php">hash_hmac()</a> function.</p>
+<p>Stronger algorithms of course will be added in the future as they
+appear and become widely available.</p>
+</div>
+</div>
+</div>
+<div class="section" id="class-reference">
+<h2><a class="toc-backref" href="#id16">Class Reference</a><a class="headerlink" href="#class-reference" title="Permalink to this headline">¶</a></h2>
+<dl class="class">
+<dt id="CI_Encryption">
+<em class="property">class </em><code class="descname">CI_Encryption</code><a class="headerlink" href="#CI_Encryption" title="Permalink to this definition">¶</a></dt>
+<dd><dl class="method">
+<dt id="CI_Encryption::initialize">
+<code class="descname">initialize</code><span class="sig-paren">(</span><em>$params</em><span class="sig-paren">)</span><a class="headerlink" href="#CI_Encryption::initialize" title="Permalink to this definition">¶</a></dt>
+<dd><table class="docutils field-list" frame="void" rules="none">
+<col class="field-name" />
+<col class="field-body" />
+<tbody valign="top">
+<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
+<li><strong>$params</strong> (<em>array</em>) – Configuration parameters</li>
+</ul>
+</td>
+</tr>
+<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">CI_Encryption instance (method chaining)</p>
+</td>
+</tr>
+<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">CI_Encryption</p>
+</td>
+</tr>
+</tbody>
+</table>
+<p>Initializes (configures) the library to use a different
+driver, cipher, mode or key.</p>
+<p>Example:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">initialize</span><span class="p">(</span>
+        <span class="k">array</span><span class="p">(</span><span class="s1">&#39;mode&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;ctr&#39;</span><span class="p">)</span>
+<span class="p">);</span>
+</pre></div>
+</div>
+<p>Please refer to the <a class="reference internal" href="#configuration"><span class="std std-ref">Configuring the library</span></a> section for detailed info.</p>
+</dd></dl>
+
+<dl class="method">
+<dt id="CI_Encryption::encrypt">
+<code class="descname">encrypt</code><span class="sig-paren">(</span><em>$data</em><span class="optional">[</span>, <em>$params = NULL</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#CI_Encryption::encrypt" title="Permalink to this definition">¶</a></dt>
+<dd><table class="docutils field-list" frame="void" rules="none">
+<col class="field-name" />
+<col class="field-body" />
+<tbody valign="top">
+<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
+<li><strong>$data</strong> (<em>string</em>) – Data to encrypt</li>
+<li><strong>$params</strong> (<em>array</em>) – Optional parameters</li>
+</ul>
+</td>
+</tr>
+<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">Encrypted data or FALSE on failure</p>
+</td>
+</tr>
+<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">string</p>
+</td>
+</tr>
+</tbody>
+</table>
+<p>Encrypts the input data and returns its ciphertext.</p>
+<p>Example:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$ciphertext</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">encrypt</span><span class="p">(</span><span class="s1">&#39;My secret message&#39;</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Please refer to the <a class="reference internal" href="#custom-parameters"><span class="std std-ref">Using custom parameters</span></a> section for information
+on the optional parameters.</p>
+</dd></dl>
+
+<dl class="method">
+<dt id="CI_Encryption::decrypt">
+<code class="descname">decrypt</code><span class="sig-paren">(</span><em>$data</em><span class="optional">[</span>, <em>$params = NULL</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#CI_Encryption::decrypt" title="Permalink to this definition">¶</a></dt>
+<dd><table class="docutils field-list" frame="void" rules="none">
+<col class="field-name" />
+<col class="field-body" />
+<tbody valign="top">
+<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
+<li><strong>$data</strong> (<em>string</em>) – Data to decrypt</li>
+<li><strong>$params</strong> (<em>array</em>) – Optional parameters</li>
+</ul>
+</td>
+</tr>
+<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">Decrypted data or FALSE on failure</p>
+</td>
+</tr>
+<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">string</p>
+</td>
+</tr>
+</tbody>
+</table>
+<p>Decrypts the input data and returns it in plain-text.</p>
+<p>Example:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="k">echo</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">decrypt</span><span class="p">(</span><span class="nv">$ciphertext</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Please refer to the <a class="reference internal" href="#custom-parameters"><span class="std std-ref">Using custom parameters</span></a> secrion for information
+on the optional parameters.</p>
+</dd></dl>
+
+<dl class="method">
+<dt id="CI_Encryption::create_key">
+<code class="descname">create_key</code><span class="sig-paren">(</span><em>$length</em><span class="sig-paren">)</span><a class="headerlink" href="#CI_Encryption::create_key" title="Permalink to this definition">¶</a></dt>
+<dd><table class="docutils field-list" frame="void" rules="none">
+<col class="field-name" />
+<col class="field-body" />
+<tbody valign="top">
+<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
+<li><strong>$length</strong> (<em>int</em>) – Output length</li>
+</ul>
+</td>
+</tr>
+<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">A pseudo-random cryptographic key with the specified length, or FALSE on failure</p>
+</td>
+</tr>
+<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">string</p>
+</td>
+</tr>
+</tbody>
+</table>
+<p>Creates a cryptographic key by fetching random data from
+the operating system’s sources (i.e. /dev/urandom).</p>
+</dd></dl>
+
+<dl class="method">
+<dt id="CI_Encryption::hkdf">
+<code class="descname">hkdf</code><span class="sig-paren">(</span><em>$key</em><span class="optional">[</span>, <em>$digest = 'sha512'</em><span class="optional">[</span>, <em>$salt = NULL</em><span class="optional">[</span>, <em>$length = NULL</em><span class="optional">[</span>, <em>$info = ''</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#CI_Encryption::hkdf" title="Permalink to this definition">¶</a></dt>
+<dd><table class="docutils field-list" frame="void" rules="none">
+<col class="field-name" />
+<col class="field-body" />
+<tbody valign="top">
+<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
+<li><strong>$key</strong> (<em>string</em>) – Input key material</li>
+<li><strong>$digest</strong> (<em>string</em>) – A SHA-2 family digest algorithm</li>
+<li><strong>$salt</strong> (<em>string</em>) – Optional salt</li>
+<li><strong>$length</strong> (<em>int</em>) – Optional output length</li>
+<li><strong>$info</strong> (<em>string</em>) – Optional context/application-specific info</li>
+</ul>
+</td>
+</tr>
+<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">A pseudo-random key or FALSE on failure</p>
+</td>
+</tr>
+<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">string</p>
+</td>
+</tr>
+</tbody>
+</table>
+<p>Derives a key from another, presumably weaker key.</p>
+<p>This method is used internally to derive an encryption and HMAC key
+from your configured <em>encryption_key</em>.</p>
+<p>It is publicly available due to its otherwise general purpose. It is
+described in <a class="reference external" href="https://tools.ietf.org/rfc/rfc5869.txt">RFC 5869</a>.</p>
+<p>However, as opposed to the description in RFC 5869, this implementation
+doesn’t support SHA1.</p>
+<p>Example:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$hmac_key</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">hkdf</span><span class="p">(</span>
+        <span class="nv">$key</span><span class="p">,</span>
+        <span class="s1">&#39;sha512&#39;</span><span class="p">,</span>
+        <span class="k">NULL</span><span class="p">,</span>
+        <span class="k">NULL</span><span class="p">,</span>
+        <span class="s1">&#39;authentication&#39;</span>
+<span class="p">);</span>
+
+<span class="c1">// $hmac_key is a pseudo-random key with a length of 64 bytes</span>
+</pre></div>
+</div>
+</dd></dl>
+
+</dd></dl>
+
+</div>
+</div>
+
+
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+      Last updated on Jan 16, 2019.
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