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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">$this->load->library()</span></code> |
| method:</p> |
| <div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-></span><span class="na">load</span><span class="o">-></span><span class="na">library</span><span class="p">(</span><span class="s1">'encryption'</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">-></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">$this</span><span class="o">-></span><span class="na">encryption</span><span class="o">-></span><span class="na">create_key</span><span class="p">(</span><span class="mi">16</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>The key can be either stored in your <em>application/config/config.php</em>, or |
| you can design your own storage mechanism and pass the key dynamically |
| when encrypting/decrypting.</p> |
| <p>To save your key to your <em>application/config/config.php</em>, open the file |
| and set:</p> |
| <div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$config</span><span class="p">[</span><span class="s1">'encryption_key'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'YOUR KEY'</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">-></span><span class="na">encryption</span><span class="o">-></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">'encryption_key'</span><span class="p">]</span> <span class="o">=</span> <span class="nb">hex2bin</span><span class="p">(</span><span class="o"><</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">></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">$this</span><span class="o">-></span><span class="na">encryption</span><span class="o">-></span><span class="na">initialize</span><span class="p">(</span> |
| <span class="k">array</span><span class="p">(</span> |
| <span class="s1">'cipher'</span> <span class="o">=></span> <span class="s1">'aes-256'</span><span class="p">,</span> |
| <span class="s1">'mode'</span> <span class="o">=></span> <span class="s1">'ctr'</span><span class="p">,</span> |
| <span class="s1">'key'</span> <span class="o">=></span> <span class="s1">'<a 32-character random string>'</span> |
| <span class="p">)</span> |
| <span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>Note that we only mentioned that you want to change the ciper and mode, |
| but we also included a key in the example. As previously noted, it is |
| important that you choose a key with a proper size for the used algorithm.</p> |
| <p>There’s also the ability to change the driver, if for some reason you |
| have both, but want to use MCrypt instead of OpenSSL:</p> |
| <div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// Switch to the MCrypt driver</span> |
| <span class="nv">$this</span><span class="o">-></span><span class="na">encryption</span><span class="o">-></span><span class="na">initialize</span><span class="p">(</span><span class="k">array</span><span class="p">(</span><span class="s1">'driver'</span> <span class="o">=></span> <span class="s1">'mcrypt'</span><span class="p">));</span> |
| |
| <span class="c1">// Switch back to the OpenSSL driver</span> |
| <span class="nv">$this</span><span class="o">-></span><span class="na">encryption</span><span class="o">-></span><span class="na">initialize</span><span class="p">(</span><span class="k">array</span><span class="p">(</span><span class="s1">'driver'</span> <span class="o">=></span> <span class="s1">'openssl'</span><span class="p">));</span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="encrypting-and-decrypting-data"> |
| <h3><a class="toc-backref" href="#id12">Encrypting and decrypting data</a><a class="headerlink" href="#encrypting-and-decrypting-data" title="Permalink to this headline">¶</a></h3> |
| <p>Encrypting and decrypting data with the already configured library |
| settings is simple. As simple as just passing the string to the |
| <code class="docutils literal"><span class="pre">encrypt()</span></code> and/or <code class="docutils literal"><span class="pre">decrypt()</span></code> methods:</p> |
| <div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$plain_text</span> <span class="o">=</span> <span class="s1">'This is a plain-text message!'</span><span class="p">;</span> |
| <span class="nv">$ciphertext</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-></span><span class="na">encryption</span><span class="o">-></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">-></span><span class="na">encryption</span><span class="o">-></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->encryption->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->encryption->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">$this</span><span class="o">-></span><span class="na">encryption</span><span class="o">-></span><span class="na">decrypt</span><span class="p">(</span> |
| <span class="nv">$ciphertext</span><span class="p">,</span> |
| <span class="k">array</span><span class="p">(</span> |
| <span class="s1">'cipher'</span> <span class="o">=></span> <span class="s1">'blowfish'</span><span class="p">,</span> |
| <span class="s1">'mode'</span> <span class="o">=></span> <span class="s1">'cbc'</span><span class="p">,</span> |
| <span class="s1">'key'</span> <span class="o">=></span> <span class="nv">$key</span><span class="p">,</span> |
| <span class="s1">'hmac_digest'</span> <span class="o">=></span> <span class="s1">'sha256'</span><span class="p">,</span> |
| <span class="s1">'hmac_key'</span> <span class="o">=></span> <span class="nv">$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">$this</span><span class="o">-></span><span class="na">encryption</span><span class="o">-></span><span class="na">initialize</span><span class="p">(</span> |
| <span class="k">array</span><span class="p">(</span><span class="s1">'mode'</span> <span class="o">=></span> <span class="s1">'ctr'</span><span class="p">)</span> |
| <span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>Please refer to the <a class="reference internal" href="#configuration"><span class="std std-ref">Configuring the library</span></a> section for detailed info.</p> |
| </dd></dl> |
| |
| <dl class="method"> |
| <dt id="CI_Encryption::encrypt"> |
| <code class="descname">encrypt</code><span class="sig-paren">(</span><em>$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">$this</span><span class="o">-></span><span class="na">encryption</span><span class="o">-></span><span class="na">encrypt</span><span class="p">(</span><span class="s1">'My secret message'</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>Please refer to the <a class="reference internal" href="#custom-parameters"><span class="std std-ref">Using custom parameters</span></a> section for information |
| on the optional parameters.</p> |
| </dd></dl> |
| |
| <dl class="method"> |
| <dt id="CI_Encryption::decrypt"> |
| <code class="descname">decrypt</code><span class="sig-paren">(</span><em>$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">-></span><span class="na">encryption</span><span class="o">-></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">$this</span><span class="o">-></span><span class="na">encryption</span><span class="o">-></span><span class="na">hkdf</span><span class="p">(</span> |
| <span class="nv">$key</span><span class="p">,</span> |
| <span class="s1">'sha512'</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">'authentication'</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> |
| |
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