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425 <div class="section" id="encryption-library">
426<h1>Encryption Library<a class="headerlink" href="#encryption-library" title="Permalink to this headline"></a></h1>
427<div class="admonition important">
428<p class="first admonition-title">Important</p>
429<p class="last">DO NOT use this or any other <em>encryption</em> library for
430user password storage! Passwords must be <em>hashed</em> instead, and you
431should do that via PHP’s own <a class="reference external" href="http://php.net/password">Password Hashing extension</a>.</p>
432</div>
433<p>The Encryption Library provides two-way data encryption. To do so in
434a cryptographically secure way, it utilizes PHP extensions that are
435unfortunately not always available on all systems.
436You must meet one of the following dependencies in order to use this
437library:</p>
438<ul class="simple">
439<li><a class="reference external" href="http://php.net/openssl">OpenSSL</a></li>
440<li><a class="reference external" href="http://php.net/mcrypt">MCrypt</a> (and <cite>MCRYPT_DEV_URANDOM</cite> availability)</li>
441</ul>
442<p>If neither of the above dependencies is met, we simply cannot offer
443you a good enough implementation to meet the high standards required
444for proper cryptography.</p>
445<div class="contents local topic" id="contents">
446<ul class="simple">
447<li><a class="reference internal" href="#using-the-encryption-library" id="id2">Using the Encryption Library</a><ul>
448<li><a class="reference internal" href="#initializing-the-class" id="id3">Initializing the Class</a></li>
449<li><a class="reference internal" href="#default-behavior" id="id4">Default behavior</a></li>
450<li><a class="reference internal" href="#setting-your-encryption-key" id="id5">Setting your encryption_key</a></li>
451<li><a class="reference internal" href="#supported-encryption-ciphers-and-modes" id="id6">Supported encryption ciphers and modes</a><ul>
452<li><a class="reference internal" href="#portable-ciphers" id="id7">Portable ciphers</a></li>
453<li><a class="reference internal" href="#driver-specific-ciphers" id="id8">Driver-specific ciphers</a></li>
454<li><a class="reference internal" href="#encryption-modes" id="id9">Encryption modes</a></li>
455</ul>
456</li>
457<li><a class="reference internal" href="#message-length" id="id10">Message Length</a></li>
458<li><a class="reference internal" href="#configuring-the-library" id="id11">Configuring the library</a></li>
459<li><a class="reference internal" href="#encrypting-and-decrypting-data" id="id12">Encrypting and decrypting data</a><ul>
460<li><a class="reference internal" href="#how-it-works" id="id13">How it works</a></li>
461<li><a class="reference internal" href="#using-custom-parameters" id="id14">Using custom parameters</a></li>
462<li><a class="reference internal" href="#supported-hmac-authentication-algorithms" id="id15">Supported HMAC authentication algorithms</a></li>
463</ul>
464</li>
465</ul>
466</li>
467<li><a class="reference internal" href="#class-reference" id="id16">Class Reference</a></li>
468</ul>
469</div>
470<div class="custom-index container"></div><div class="section" id="using-the-encryption-library">
471<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>
472<div class="section" id="initializing-the-class">
473<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>
474<p>Like most other classes in CodeIgniter, the Encryption library is
475initialized in your controller using the <code class="docutils literal"><span class="pre">$this-&gt;load-&gt;library()</span></code>
476method:</p>
477<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$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>
478</pre></div>
479</div>
480<p>Once loaded, the Encryption library object will be available using:</p>
481<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>
482</pre></div>
483</div>
484</div>
485<div class="section" id="default-behavior">
486<h3><a class="toc-backref" href="#id4">Default behavior</a><a class="headerlink" href="#default-behavior" title="Permalink to this headline"></a></h3>
487<p>By default, the Encryption Library will use the AES-128 cipher in CBC
488mode, using your configured <em>encryption_key</em> and SHA512 HMAC authentication.</p>
489<div class="admonition note">
490<p class="first admonition-title">Note</p>
491<p class="last">AES-128 is chosen both because it is proven to be strong and
492because of its wide availability across different cryptographic
493software and programming languages’ APIs.</p>
494</div>
495<p>However, the <em>encryption_key</em> is not used as is.</p>
496<p>If you are somewhat familiar with cryptography, you should already know
497that a HMAC also requires a secret key and using the same key for both
498encryption and authentication is a bad practice.</p>
499<p>Because of that, two separate keys are derived from your already configured
500<em>encryption_key</em>: one for encryption and one for authentication. This is
501done via a technique called <a class="reference external" href="http://en.wikipedia.org/wiki/HKDF">HMAC-based Key Derivation Function</a> (HKDF).</p>
502</div>
503<div class="section" id="setting-your-encryption-key">
504<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>
505<p>An <em>encryption key</em> is a piece of information that controls the
506cryptographic process and permits a plain-text string to be encrypted,
507and afterwards - decrypted. It is the secret “ingredient” in the whole
508process that allows you to be the only one who is able to decrypt data
509that you’ve decided to hide from the eyes of the public.
510After one key is used to encrypt data, that same key provides the <strong>only</strong>
511means to decrypt it, so not only must you chose one carefully, but you
512must not lose it or you will also lose access to the data.</p>
513<p>It must be noted that to ensure maximum security, such key <em>should</em> not
514only be as strong as possible, but also often changed. Such behavior
515however is rarely practical or possible to implement, and that is why
516CodeIgniter gives you the ability to configure a single key that is to be
517used (almost) every time.</p>
518<p>It goes without saying that you should guard your key carefully. Should
519someone gain access to your key, the data will be easily decrypted. If
520your server is not totally under your control it’s impossible to ensure
521key security so you may want to think carefully before using it for
522anything that requires high security, like storing credit card numbers.</p>
523<p>Your encryption key <strong>must</strong> be as long as the encyption algorithm in use
524allows. For AES-128, that’s 128 bits or 16 bytes (charcters) long.
525You will find a table below that shows the supported key lengths of
526different ciphers.</p>
527<p>The key should be as random as possible and it <strong>must not</strong> be a regular
528text string, nor the output of a hashing function, etc. In order to create
529a proper key, you must use the Encryption library’s <code class="docutils literal"><span class="pre">create_key()</span></code> method</p>
530<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// $key will be assigned a 16-byte (128-bit) random key</span>
531<span class="nv">$key</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">create_key</span><span class="p">(</span><span class="mi">16</span><span class="p">);</span>
532</pre></div>
533</div>
534<p>The key can be either stored in your <em>application/config/config.php</em>, or
535you can design your own storage mechanism and pass the key dynamically
536when encrypting/decrypting.</p>
537<p>To save your key to your <em>application/config/config.php</em>, open the file
538and set:</p>
539<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$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>
540</pre></div>
541</div>
542<p>You’ll notice that the <code class="docutils literal"><span class="pre">create_key()</span></code> method outputs binary data, which
543is hard to deal with (i.e. a copy-paste may damage it), so you may use
544<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
545a more friendly manner. For example:</p>
546<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// Get a hex-encoded representation of the key:</span>
547<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>
548
549<span class="c1">// Put the same value in your config with hex2bin(),</span>
550<span class="c1">// so that it is still passed as binary to the library:</span>
551<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>
552</pre></div>
553</div>
554</div>
555<div class="section" id="supported-encryption-ciphers-and-modes">
556<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>
557<div class="admonition note">
558<p class="first admonition-title">Note</p>
559<p class="last">The terms ‘cipher’ and ‘encryption algorithm’ are interchangeable.</p>
560</div>
561<div class="section" id="portable-ciphers">
562<h4><a class="toc-backref" href="#id7">Portable ciphers</a><a class="headerlink" href="#portable-ciphers" title="Permalink to this headline"></a></h4>
563<p>Because MCrypt and OpenSSL (also called drivers throughout this document)
564each support different sets of encryption algorithms and often implement
565them in different ways, our Encryption library is designed to use them in
566a portable fashion, or in other words - it enables you to use them
567interchangeably, at least for the ciphers supported by both drivers.</p>
568<p>It is also implemented in a way that aims to match the standard
569implementations in other programming languages and libraries.</p>
570<p>Here’s a list of the so called “portable” ciphers, where
571“CodeIgniter name” is the string value that you’d have to pass to the
572Encryption library to use that cipher:</p>
573<table border="1" class="docutils">
574<colgroup>
575<col width="24%" />
576<col width="18%" />
577<col width="28%" />
578<col width="31%" />
579</colgroup>
580<thead valign="bottom">
581<tr class="row-odd"><th class="head">Cipher name</th>
582<th class="head">CodeIgniter name</th>
583<th class="head">Key lengths (bits / bytes)</th>
584<th class="head">Supported modes</th>
585</tr>
586</thead>
587<tbody valign="top">
588<tr class="row-even"><td>AES-128 / Rijndael-128</td>
589<td>aes-128</td>
590<td>128 / 16</td>
591<td>CBC, CTR, CFB, CFB8, OFB, ECB</td>
592</tr>
593<tr class="row-odd"><td>AES-192</td>
594<td>aes-192</td>
595<td>192 / 24</td>
596<td>CBC, CTR, CFB, CFB8, OFB, ECB</td>
597</tr>
598<tr class="row-even"><td>AES-256</td>
599<td>aes-256</td>
600<td>256 / 32</td>
601<td>CBC, CTR, CFB, CFB8, OFB, ECB</td>
602</tr>
603<tr class="row-odd"><td>DES</td>
604<td>des</td>
605<td>56 / 7</td>
606<td>CBC, CFB, CFB8, OFB, ECB</td>
607</tr>
608<tr class="row-even"><td>TripleDES</td>
609<td>tripledes</td>
610<td>56 / 7, 112 / 14, 168 / 21</td>
611<td>CBC, CFB, CFB8, OFB</td>
612</tr>
613<tr class="row-odd"><td>Blowfish</td>
614<td>blowfish</td>
615<td>128-448 / 16-56</td>
616<td>CBC, CFB, OFB, ECB</td>
617</tr>
618<tr class="row-even"><td>CAST5 / CAST-128</td>
619<td>cast5</td>
620<td>88-128 / 11-16</td>
621<td>CBC, CFB, OFB, ECB</td>
622</tr>
623<tr class="row-odd"><td>RC4 / ARCFour</td>
624<td>rc4</td>
625<td>40-2048 / 5-256</td>
626<td>Stream</td>
627</tr>
628</tbody>
629</table>
630<div class="admonition important">
631<p class="first admonition-title">Important</p>
632<p class="last">Because of how MCrypt works, if you fail to provide a key
633with the appropriate length, you might end up using a different
634algorithm than the one configured, so be really careful with that!</p>
635</div>
636<div class="admonition note">
637<p class="first admonition-title">Note</p>
638<p class="last">In case it isn’t clear from the above table, Blowfish, CAST5
639and RC4 support variable length keys. That is, any number in the
640shown ranges is valid, although in bit terms that only happens
641in 8-bit increments.</p>
642</div>
643<div class="admonition note">
644<p class="first admonition-title">Note</p>
645<p class="last">Even though CAST5 supports key lengths lower than 128 bits
646(16 bytes), in fact they will just be zero-padded to the
647maximum length, as specified in <a class="reference external" href="http://tools.ietf.org/rfc/rfc2144.txt">RFC 2144</a>.</p>
648</div>
649<div class="admonition note">
650<p class="first admonition-title">Note</p>
651<p class="last">Blowfish supports key lengths as small as 32 bits (4 bytes), but
652our tests have shown that only lengths of 128 bits (16 bytes) or
653higher are properly supported by both MCrypt and OpenSSL. It is
654also a bad practice to use such low-length keys anyway.</p>
655</div>
656</div>
657<div class="section" id="driver-specific-ciphers">
658<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>
659<p>As noted above, MCrypt and OpenSSL support different sets of encryption
660ciphers. For portability reasons and because we haven’t tested them
661properly, we do not advise you to use the ones that are driver-specific,
662but regardless, here’s a list of most of them:</p>
663<table border="1" class="docutils">
664<colgroup>
665<col width="15%" />
666<col width="10%" />
667<col width="32%" />
668<col width="44%" />
669</colgroup>
670<thead valign="bottom">
671<tr class="row-odd"><th class="head">Cipher name</th>
672<th class="head">Driver</th>
673<th class="head">Key lengths (bits / bytes)</th>
674<th class="head">Supported modes</th>
675</tr>
676</thead>
677<tbody valign="top">
678<tr class="row-even"><td>AES-128</td>
679<td>OpenSSL</td>
680<td>128 / 16</td>
681<td>CBC, CTR, CFB, CFB8, OFB, ECB, XTS</td>
682</tr>
683<tr class="row-odd"><td>AES-192</td>
684<td>OpenSSL</td>
685<td>192 / 24</td>
686<td>CBC, CTR, CFB, CFB8, OFB, ECB, XTS</td>
687</tr>
688<tr class="row-even"><td>AES-256</td>
689<td>OpenSSL</td>
690<td>256 / 32</td>
691<td>CBC, CTR, CFB, CFB8, OFB, ECB, XTS</td>
692</tr>
693<tr class="row-odd"><td>Rijndael-128</td>
694<td>MCrypt</td>
695<td>128 / 16, 192 / 24, 256 / 32</td>
696<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
697</tr>
698<tr class="row-even"><td>Rijndael-192</td>
699<td>MCrypt</td>
700<td>128 / 16, 192 / 24, 256 / 32</td>
701<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
702</tr>
703<tr class="row-odd"><td>Rijndael-256</td>
704<td>MCrypt</td>
705<td>128 / 16, 192 / 24, 256 / 32</td>
706<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
707</tr>
708<tr class="row-even"><td>GOST</td>
709<td>MCrypt</td>
710<td>256 / 32</td>
711<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
712</tr>
713<tr class="row-odd"><td>Twofish</td>
714<td>MCrypt</td>
715<td>128 / 16, 192 / 24, 256 / 32</td>
716<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
717</tr>
718<tr class="row-even"><td>CAST-128</td>
719<td>MCrypt</td>
720<td>40-128 / 5-16</td>
721<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
722</tr>
723<tr class="row-odd"><td>CAST-256</td>
724<td>MCrypt</td>
725<td>128 / 16, 192 / 24, 256 / 32</td>
726<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
727</tr>
728<tr class="row-even"><td>Loki97</td>
729<td>MCrypt</td>
730<td>128 / 16, 192 / 24, 256 / 32</td>
731<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
732</tr>
733<tr class="row-odd"><td>SaferPlus</td>
734<td>MCrypt</td>
735<td>128 / 16, 192 / 24, 256 / 32</td>
736<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
737</tr>
738<tr class="row-even"><td>Serpent</td>
739<td>MCrypt</td>
740<td>128 / 16, 192 / 24, 256 / 32</td>
741<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
742</tr>
743<tr class="row-odd"><td>XTEA</td>
744<td>MCrypt</td>
745<td>128 / 16</td>
746<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
747</tr>
748<tr class="row-even"><td>RC2</td>
749<td>MCrypt</td>
750<td>8-1024 / 1-128</td>
751<td>CBC, CTR, CFB, CFB8, OFB, OFB8, ECB</td>
752</tr>
753<tr class="row-odd"><td>RC2</td>
754<td>OpenSSL</td>
755<td>8-1024 / 1-128</td>
756<td>CBC, CFB, OFB, ECB</td>
757</tr>
758<tr class="row-even"><td>Camellia-128</td>
759<td>OpenSSL</td>
760<td>128 / 16</td>
761<td>CBC, CFB, CFB8, OFB, ECB</td>
762</tr>
763<tr class="row-odd"><td>Camellia-192</td>
764<td>OpenSSL</td>
765<td>192 / 24</td>
766<td>CBC, CFB, CFB8, OFB, ECB</td>
767</tr>
768<tr class="row-even"><td>Camellia-256</td>
769<td>OpenSSL</td>
770<td>256 / 32</td>
771<td>CBC, CFB, CFB8, OFB, ECB</td>
772</tr>
773<tr class="row-odd"><td>Seed</td>
774<td>OpenSSL</td>
775<td>128 / 16</td>
776<td>CBC, CFB, OFB, ECB</td>
777</tr>
778</tbody>
779</table>
780<div class="admonition note">
781<p class="first admonition-title">Note</p>
782<p class="last">If you wish to use one of those ciphers, you’d have to pass
783its name in lower-case to the Encryption library.</p>
784</div>
785<div class="admonition note">
786<p class="first admonition-title">Note</p>
787<p class="last">You’ve probably noticed that all AES cipers (and Rijndael-128)
788are also listed in the portable ciphers list. This is because
789drivers support different modes for these ciphers. Also, it is
790important to note that AES-128 and Rijndael-128 are actually
791the same cipher, but <strong>only</strong> when used with a 128-bit key.</p>
792</div>
793<div class="admonition note">
794<p class="first admonition-title">Note</p>
795<p class="last">CAST-128 / CAST-5 is also listed in both the portable and
796driver-specific ciphers list. This is because OpenSSL’s
797implementation doesn’t appear to be working correctly with
798key sizes of 80 bits and lower.</p>
799</div>
800<div class="admonition note">
801<p class="first admonition-title">Note</p>
802<p class="last">RC2 is listed as supported by both MCrypt and OpenSSL.
803However, both drivers implement them differently and they
804are not portable. It is probably worth noting that we only
805found one obscure source confirming that it is MCrypt that
806is not properly implementing it.</p>
807</div>
808</div>
809<div class="section" id="encryption-modes">
810<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>
811<p>Different modes of encryption have different characteristics and serve
812for different purposes. Some are stronger than others, some are faster
813and some offer extra features.
814We are not going in depth into that here, we’ll leave that to the
815cryptography experts. The table below is to provide brief informational
816reference to our more experienced users. If you are a beginner, just
817stick to the CBC mode - it is widely accepted as strong and secure for
818general purposes.</p>
819<table border="1" class="docutils">
820<colgroup>
821<col width="6%" />
822<col width="9%" />
823<col width="9%" />
824<col width="76%" />
825</colgroup>
826<thead valign="bottom">
827<tr class="row-odd"><th class="head">Mode name</th>
828<th class="head">CodeIgniter name</th>
829<th class="head">Driver support</th>
830<th class="head">Additional info</th>
831</tr>
832</thead>
833<tbody valign="top">
834<tr class="row-even"><td>CBC</td>
835<td>cbc</td>
836<td>MCrypt, OpenSSL</td>
837<td>A safe default choice</td>
838</tr>
839<tr class="row-odd"><td>CTR</td>
840<td>ctr</td>
841<td>MCrypt, OpenSSL</td>
842<td>Considered as theoretically better than CBC, but not as widely available</td>
843</tr>
844<tr class="row-even"><td>CFB</td>
845<td>cfb</td>
846<td>MCrypt, OpenSSL</td>
847<td>N/A</td>
848</tr>
849<tr class="row-odd"><td>CFB8</td>
850<td>cfb8</td>
851<td>MCrypt, OpenSSL</td>
852<td>Same as CFB, but operates in 8-bit mode (not recommended).</td>
853</tr>
854<tr class="row-even"><td>OFB</td>
855<td>ofb</td>
856<td>MCrypt, OpenSSL</td>
857<td>N/A</td>
858</tr>
859<tr class="row-odd"><td>OFB8</td>
860<td>ofb8</td>
861<td>MCrypt</td>
862<td>Same as OFB, but operates in 8-bit mode (not recommended).</td>
863</tr>
864<tr class="row-even"><td>ECB</td>
865<td>ecb</td>
866<td>MCrypt, OpenSSL</td>
867<td>Ignores IV (not recommended).</td>
868</tr>
869<tr class="row-odd"><td>XTS</td>
870<td>xts</td>
871<td>OpenSSL</td>
872<td>Usually used for encrypting random access data such as RAM or hard-disk storage.</td>
873</tr>
874<tr class="row-even"><td>Stream</td>
875<td>stream</td>
876<td>MCrypt, OpenSSL</td>
877<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>
878</tr>
879</tbody>
880</table>
881</div>
882</div>
883<div class="section" id="message-length">
884<h3><a class="toc-backref" href="#id10">Message Length</a><a class="headerlink" href="#message-length" title="Permalink to this headline"></a></h3>
885<p>It’s probably important for you to know that an encrypted string is usually
886longer than the original, plain-text string (depending on the cipher).</p>
887<p>This is influenced by the cipher algorithm itself, the IV prepended to the
888cipher-text and the HMAC authentication message that is also prepended.
889Furthermore, the encrypted message is also Base64-encoded so that it is safe
890for storage and transmission, regardless of a possible character set in use.</p>
891<p>Keep this information in mind when selecting your data storage mechanism.
892Cookies, for example, can only hold 4K of information.</p>
893</div>
894<div class="section" id="configuring-the-library">
895<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>
896<p>For usability, performance, but also historical reasons tied to our old
897<a class="reference internal" href="encrypt.html"><span class="doc">Encrypt Class</span></a>, the Encryption library is designed to
898use repeatedly the same driver, encryption cipher, mode and key.</p>
899<p>As noted in the “Default behavior” section above, this means using an
900auto-detected driver (OpenSSL has a higher priority), the AES-128 ciper
901in CBC mode, and your <code class="docutils literal"><span class="pre">$config['encryption_key']</span></code> value.</p>
902<p>If you wish to change that however, you need to use the <code class="docutils literal"><span class="pre">initialize()</span></code>
903method. It accepts an associative array of parameters, all of which are
904optional:</p>
905<table border="1" class="docutils">
906<colgroup>
907<col width="15%" />
908<col width="85%" />
909</colgroup>
910<thead valign="bottom">
911<tr class="row-odd"><th class="head">Option</th>
912<th class="head">Possible values</th>
913</tr>
914</thead>
915<tbody valign="top">
916<tr class="row-even"><td>driver</td>
917<td>‘mcrypt’, ‘openssl’</td>
918</tr>
919<tr class="row-odd"><td>cipher</td>
920<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>
921</tr>
922<tr class="row-even"><td>mode</td>
923<td>Encryption mode (see <a class="reference internal" href="#encryption-modes"><span class="std std-ref">Encryption modes</span></a>)</td>
924</tr>
925<tr class="row-odd"><td>key</td>
926<td>Encryption key</td>
927</tr>
928</tbody>
929</table>
930<p>For example, if you were to change the encryption algorithm and
931mode to AES-256 in CTR mode, this is what you should do:</p>
932<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">initialize</span><span class="p">(</span>
933 <span class="k">array</span><span class="p">(</span>
934 <span class="s1">&#39;cipher&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;aes-256&#39;</span><span class="p">,</span>
935 <span class="s1">&#39;mode&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;ctr&#39;</span><span class="p">,</span>
936 <span class="s1">&#39;key&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;&lt;a 32-character random string&gt;&#39;</span>
937 <span class="p">)</span>
938<span class="p">);</span>
939</pre></div>
940</div>
941<p>Note that we only mentioned that you want to change the ciper and mode,
942but we also included a key in the example. As previously noted, it is
943important that you choose a key with a proper size for the used algorithm.</p>
944<p>There’s also the ability to change the driver, if for some reason you
945have both, but want to use MCrypt instead of OpenSSL:</p>
946<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// Switch to the MCrypt driver</span>
947<span class="nv">$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>
948
949<span class="c1">// Switch back to the OpenSSL driver</span>
950<span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">initialize</span><span class="p">(</span><span class="k">array</span><span class="p">(</span><span class="s1">&#39;driver&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;openssl&#39;</span><span class="p">));</span>
951</pre></div>
952</div>
953</div>
954<div class="section" id="encrypting-and-decrypting-data">
955<h3><a class="toc-backref" href="#id12">Encrypting and decrypting data</a><a class="headerlink" href="#encrypting-and-decrypting-data" title="Permalink to this headline"></a></h3>
956<p>Encrypting and decrypting data with the already configured library
957settings is simple. As simple as just passing the string to the
958<code class="docutils literal"><span class="pre">encrypt()</span></code> and/or <code class="docutils literal"><span class="pre">decrypt()</span></code> methods:</p>
959<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$plain_text</span> <span class="o">=</span> <span class="s1">&#39;This is a plain-text message!&#39;</span><span class="p">;</span>
960<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">$plain_text</span><span class="p">);</span>
961
962<span class="c1">// Outputs: This is a plain-text message!</span>
963<span class="k">echo</span> <span class="nv">$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">$ciphertext</span><span class="p">);</span>
964</pre></div>
965</div>
966<p>And that’s it! The Encryption library will do everything necessary
967for the whole process to be cryptographically secure out-of-the-box.
968You don’t need to worry about it.</p>
969<div class="admonition important">
970<p class="first admonition-title">Important</p>
971<p class="last">Both methods will return FALSE in case of an error.
972While for <code class="docutils literal"><span class="pre">encrypt()</span></code> this can only mean incorrect
973configuration, you should always check the return value
974of <code class="docutils literal"><span class="pre">decrypt()</span></code> in production code.</p>
975</div>
976<div class="section" id="how-it-works">
977<h4><a class="toc-backref" href="#id13">How it works</a><a class="headerlink" href="#how-it-works" title="Permalink to this headline"></a></h4>
978<p>If you must know how the process works, here’s what happens under
979the hood:</p>
980<ul class="simple">
981<li><code class="docutils literal"><span class="pre">$this-&gt;encryption-&gt;encrypt($plain_text)</span></code><ol class="arabic">
982<li>Derive an encryption key and a HMAC key from your configured
983<em>encryption_key</em> via HKDF, using the SHA-512 digest algorithm.</li>
984<li>Generate a random initialization vector (IV).</li>
985<li>Encrypt the data via AES-128 in CBC mode (or another previously
986configured cipher and mode), using the above-mentioned derived
987encryption key and IV.</li>
988<li>Prepend said IV to the resulting cipher-text.</li>
989<li>Base64-encode the resulting string, so that it can be safely
990stored or transferred without worrying about character sets.</li>
991<li>Create a SHA-512 HMAC authentication message using the derived
992HMAC key to ensure data integrity and prepend it to the Base64
993string.</li>
994</ol>
995</li>
996<li><code class="docutils literal"><span class="pre">$this-&gt;encryption-&gt;decrypt($ciphertext)</span></code><ol class="arabic">
997<li>Derive an encryption key and a HMAC key from your configured
998<em>encryption_key</em> via HKDF, using the SHA-512 digest algorithm.
999Because your configured <em>encryption_key</em> is the same, this
1000will produce the same result as in the <code class="docutils literal"><span class="pre">encrypt()</span></code> method
1001above - otherwise you won’t be able to decrypt it.</li>
1002<li>Check if the string is long enough, separate the HMAC out of
1003it and validate if it is correct (this is done in a way that
1004prevents timing attacks against it). Return FALSE if either of
1005the checks fails.</li>
1006<li>Base64-decode the string.</li>
1007<li>Separate the IV out of the cipher-text and decrypt the said
1008cipher-text using that IV and the derived encryption key.</li>
1009</ol>
1010</li>
1011</ul>
1012</div>
1013<div class="section" id="using-custom-parameters">
1014<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>
1015<p>Let’s say you have to interact with another system that is out
1016of your control and uses another method to encrypt data. A
1017method that will most certainly not match the above-described
1018sequence and probably not use all of the steps either.</p>
1019<p>The Encryption library allows you to change how its encryption
1020and decryption processes work, so that you can easily tailor a
1021custom solution for such situations.</p>
1022<div class="admonition note">
1023<p class="first admonition-title">Note</p>
1024<p class="last">It is possible to use the library in this way, without
1025setting an <em>encryption_key</em> in your configuration file.</p>
1026</div>
1027<p>All you have to do is to pass an associative array with a few
1028parameters 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.
1029Here’s an example:</p>
1030<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// Assume that we have $ciphertext, $key and $hmac_key</span>
1031<span class="c1">// from on outside source</span>
1032
1033<span class="nv">$message</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">decrypt</span><span class="p">(</span>
1034 <span class="nv">$ciphertext</span><span class="p">,</span>
1035 <span class="k">array</span><span class="p">(</span>
1036 <span class="s1">&#39;cipher&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;blowfish&#39;</span><span class="p">,</span>
1037 <span class="s1">&#39;mode&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;cbc&#39;</span><span class="p">,</span>
1038 <span class="s1">&#39;key&#39;</span> <span class="o">=&gt;</span> <span class="nv">$key</span><span class="p">,</span>
1039 <span class="s1">&#39;hmac_digest&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;sha256&#39;</span><span class="p">,</span>
1040 <span class="s1">&#39;hmac_key&#39;</span> <span class="o">=&gt;</span> <span class="nv">$hmac_key</span>
1041 <span class="p">)</span>
1042<span class="p">);</span>
1043</pre></div>
1044</div>
1045<p>In the above example, we are decrypting a message that was encrypted
1046using the Blowfish cipher in CBC mode and authenticated via a SHA-256
1047HMAC.</p>
1048<div class="admonition important">
1049<p class="first admonition-title">Important</p>
1050<p class="last">Note that both ‘key’ and ‘hmac_key’ are used in this
1051example. When using custom parameters, encryption and HMAC keys
1052are not derived like the default behavior of the library is.</p>
1053</div>
1054<p>Below is a list of the available options.</p>
1055<p>However, unless you really need to and you know what you are doing,
1056we advise you to not change the encryption process as this could
1057impact security, so please do so with caution.</p>
1058<table border="1" class="docutils">
1059<colgroup>
1060<col width="12%" />
1061<col width="14%" />
1062<col width="26%" />
1063<col width="49%" />
1064</colgroup>
1065<thead valign="bottom">
1066<tr class="row-odd"><th class="head">Option</th>
1067<th class="head">Default value</th>
1068<th class="head">Mandatory / Optional</th>
1069<th class="head">Description</th>
1070</tr>
1071</thead>
1072<tbody valign="top">
1073<tr class="row-even"><td>cipher</td>
1074<td>N/A</td>
1075<td>Yes</td>
1076<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>
1077</tr>
1078<tr class="row-odd"><td>mode</td>
1079<td>N/A</td>
1080<td>Yes</td>
1081<td>Encryption mode (see <a class="reference internal" href="#encryption-modes"><span class="std std-ref">Encryption modes</span></a>).</td>
1082</tr>
1083<tr class="row-even"><td>key</td>
1084<td>N/A</td>
1085<td>Yes</td>
1086<td>Encryption key.</td>
1087</tr>
1088<tr class="row-odd"><td>hmac</td>
1089<td>TRUE</td>
1090<td>No</td>
1091<td>Whether to use a HMAC.
1092Boolean. If set to FALSE, then <em>hmac_digest</em> and
1093<em>hmac_key</em> will be ignored.</td>
1094</tr>
1095<tr class="row-even"><td>hmac_digest</td>
1096<td>sha512</td>
1097<td>No</td>
1098<td>HMAC message digest algorithm (see <a class="reference internal" href="#digests"><span class="std std-ref">Supported HMAC authentication algorithms</span></a>).</td>
1099</tr>
1100<tr class="row-odd"><td>hmac_key</td>
1101<td>N/A</td>
1102<td>Yes, unless <em>hmac</em> is FALSE</td>
1103<td>HMAC key.</td>
1104</tr>
1105<tr class="row-even"><td>raw_data</td>
1106<td>FALSE</td>
1107<td>No</td>
1108<td>Whether the cipher-text should be raw.
1109Boolean. If set to TRUE, then Base64 encoding and
1110decoding will not be performed and HMAC will not
1111be a hexadecimal string.</td>
1112</tr>
1113</tbody>
1114</table>
1115<div class="admonition important">
1116<p class="first admonition-title">Important</p>
1117<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
1118a mandatory parameter is not provided or if a provided
1119value is incorrect. This includes <em>hmac_key</em>, unless <em>hmac</em>
1120is set to FALSE.</p>
1121</div>
1122</div>
1123<div class="section" id="supported-hmac-authentication-algorithms">
1124<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>
1125<p>For HMAC message authentication, the Encryption library supports
1126usage of the SHA-2 family of algorithms:</p>
1127<table border="1" class="docutils">
1128<colgroup>
1129<col width="19%" />
1130<col width="34%" />
1131<col width="47%" />
1132</colgroup>
1133<thead valign="bottom">
1134<tr class="row-odd"><th class="head">Algorithm</th>
1135<th class="head">Raw length (bytes)</th>
1136<th class="head">Hex-encoded length (bytes)</th>
1137</tr>
1138</thead>
1139<tbody valign="top">
1140<tr class="row-even"><td>sha512</td>
1141<td>64</td>
1142<td>128</td>
1143</tr>
1144<tr class="row-odd"><td>sha384</td>
1145<td>48</td>
1146<td>96</td>
1147</tr>
1148<tr class="row-even"><td>sha256</td>
1149<td>32</td>
1150<td>64</td>
1151</tr>
1152<tr class="row-odd"><td>sha224</td>
1153<td>28</td>
1154<td>56</td>
1155</tr>
1156</tbody>
1157</table>
1158<p>The reason for not including other popular algorithms, such as
1159MD5 or SHA1 is that they are no longer considered secure enough
1160and as such, we don’t want to encourage their usage.
1161If you absolutely need to use them, it is easy to do so via PHP’s
1162native <a class="reference external" href="http://php.net/manual/en/function.hash-hmac.php">hash_hmac()</a> function.</p>
1163<p>Stronger algorithms of course will be added in the future as they
1164appear and become widely available.</p>
1165</div>
1166</div>
1167</div>
1168<div class="section" id="class-reference">
1169<h2><a class="toc-backref" href="#id16">Class Reference</a><a class="headerlink" href="#class-reference" title="Permalink to this headline"></a></h2>
1170<dl class="class">
1171<dt id="CI_Encryption">
1172<em class="property">class </em><code class="descname">CI_Encryption</code><a class="headerlink" href="#CI_Encryption" title="Permalink to this definition"></a></dt>
1173<dd><dl class="method">
1174<dt id="CI_Encryption::initialize">
1175<code class="descname">initialize</code><span class="sig-paren">(</span><em>$params</em><span class="sig-paren">)</span><a class="headerlink" href="#CI_Encryption::initialize" title="Permalink to this definition"></a></dt>
1176<dd><table class="docutils field-list" frame="void" rules="none">
1177<col class="field-name" />
1178<col class="field-body" />
1179<tbody valign="top">
1180<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
1181<li><strong>$params</strong> (<em>array</em>) – Configuration parameters</li>
1182</ul>
1183</td>
1184</tr>
1185<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">CI_Encryption instance (method chaining)</p>
1186</td>
1187</tr>
1188<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">CI_Encryption</p>
1189</td>
1190</tr>
1191</tbody>
1192</table>
1193<p>Initializes (configures) the library to use a different
1194driver, cipher, mode or key.</p>
1195<p>Example:</p>
1196<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">initialize</span><span class="p">(</span>
1197 <span class="k">array</span><span class="p">(</span><span class="s1">&#39;mode&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;ctr&#39;</span><span class="p">)</span>
1198<span class="p">);</span>
1199</pre></div>
1200</div>
1201<p>Please refer to the <a class="reference internal" href="#configuration"><span class="std std-ref">Configuring the library</span></a> section for detailed info.</p>
1202</dd></dl>
1203
1204<dl class="method">
1205<dt id="CI_Encryption::encrypt">
1206<code class="descname">encrypt</code><span class="sig-paren">(</span><em>$data</em><span class="optional">[</span>, <em>$params = NULL</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#CI_Encryption::encrypt" title="Permalink to this definition"></a></dt>
1207<dd><table class="docutils field-list" frame="void" rules="none">
1208<col class="field-name" />
1209<col class="field-body" />
1210<tbody valign="top">
1211<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
1212<li><strong>$data</strong> (<em>string</em>) – Data to encrypt</li>
1213<li><strong>$params</strong> (<em>array</em>) – Optional parameters</li>
1214</ul>
1215</td>
1216</tr>
1217<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">Encrypted data or FALSE on failure</p>
1218</td>
1219</tr>
1220<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">string</p>
1221</td>
1222</tr>
1223</tbody>
1224</table>
1225<p>Encrypts the input data and returns its ciphertext.</p>
1226<p>Example:</p>
1227<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$ciphertext</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">encrypt</span><span class="p">(</span><span class="s1">&#39;My secret message&#39;</span><span class="p">);</span>
1228</pre></div>
1229</div>
1230<p>Please refer to the <a class="reference internal" href="#custom-parameters"><span class="std std-ref">Using custom parameters</span></a> section for information
1231on the optional parameters.</p>
1232</dd></dl>
1233
1234<dl class="method">
1235<dt id="CI_Encryption::decrypt">
1236<code class="descname">decrypt</code><span class="sig-paren">(</span><em>$data</em><span class="optional">[</span>, <em>$params = NULL</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#CI_Encryption::decrypt" title="Permalink to this definition"></a></dt>
1237<dd><table class="docutils field-list" frame="void" rules="none">
1238<col class="field-name" />
1239<col class="field-body" />
1240<tbody valign="top">
1241<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
1242<li><strong>$data</strong> (<em>string</em>) – Data to decrypt</li>
1243<li><strong>$params</strong> (<em>array</em>) – Optional parameters</li>
1244</ul>
1245</td>
1246</tr>
1247<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">Decrypted data or FALSE on failure</p>
1248</td>
1249</tr>
1250<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">string</p>
1251</td>
1252</tr>
1253</tbody>
1254</table>
1255<p>Decrypts the input data and returns it in plain-text.</p>
1256<p>Example:</p>
1257<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="k">echo</span> <span class="nv">$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">$ciphertext</span><span class="p">);</span>
1258</pre></div>
1259</div>
1260<p>Please refer to the <a class="reference internal" href="#custom-parameters"><span class="std std-ref">Using custom parameters</span></a> secrion for information
1261on the optional parameters.</p>
1262</dd></dl>
1263
1264<dl class="method">
1265<dt id="CI_Encryption::create_key">
1266<code class="descname">create_key</code><span class="sig-paren">(</span><em>$length</em><span class="sig-paren">)</span><a class="headerlink" href="#CI_Encryption::create_key" title="Permalink to this definition"></a></dt>
1267<dd><table class="docutils field-list" frame="void" rules="none">
1268<col class="field-name" />
1269<col class="field-body" />
1270<tbody valign="top">
1271<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
1272<li><strong>$length</strong> (<em>int</em>) – Output length</li>
1273</ul>
1274</td>
1275</tr>
1276<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">A pseudo-random cryptographic key with the specified length, or FALSE on failure</p>
1277</td>
1278</tr>
1279<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">string</p>
1280</td>
1281</tr>
1282</tbody>
1283</table>
1284<p>Creates a cryptographic key by fetching random data from
1285the operating system’s sources (i.e. /dev/urandom).</p>
1286</dd></dl>
1287
1288<dl class="method">
1289<dt id="CI_Encryption::hkdf">
1290<code class="descname">hkdf</code><span class="sig-paren">(</span><em>$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>
1291<dd><table class="docutils field-list" frame="void" rules="none">
1292<col class="field-name" />
1293<col class="field-body" />
1294<tbody valign="top">
1295<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
1296<li><strong>$key</strong> (<em>string</em>) – Input key material</li>
1297<li><strong>$digest</strong> (<em>string</em>) – A SHA-2 family digest algorithm</li>
1298<li><strong>$salt</strong> (<em>string</em>) – Optional salt</li>
1299<li><strong>$length</strong> (<em>int</em>) – Optional output length</li>
1300<li><strong>$info</strong> (<em>string</em>) – Optional context/application-specific info</li>
1301</ul>
1302</td>
1303</tr>
1304<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">A pseudo-random key or FALSE on failure</p>
1305</td>
1306</tr>
1307<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">string</p>
1308</td>
1309</tr>
1310</tbody>
1311</table>
1312<p>Derives a key from another, presumably weaker key.</p>
1313<p>This method is used internally to derive an encryption and HMAC key
1314from your configured <em>encryption_key</em>.</p>
1315<p>It is publicly available due to its otherwise general purpose. It is
1316described in <a class="reference external" href="https://tools.ietf.org/rfc/rfc5869.txt">RFC 5869</a>.</p>
1317<p>However, as opposed to the description in RFC 5869, this implementation
1318doesn’t support SHA1.</p>
1319<p>Example:</p>
1320<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$hmac_key</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">encryption</span><span class="o">-&gt;</span><span class="na">hkdf</span><span class="p">(</span>
1321 <span class="nv">$key</span><span class="p">,</span>
1322 <span class="s1">&#39;sha512&#39;</span><span class="p">,</span>
1323 <span class="k">NULL</span><span class="p">,</span>
1324 <span class="k">NULL</span><span class="p">,</span>
1325 <span class="s1">&#39;authentication&#39;</span>
1326<span class="p">);</span>
1327
1328<span class="c1">// $hmac_key is a pseudo-random key with a length of 64 bytes</span>
1329</pre></div>
1330</div>
1331</dd></dl>
1332
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1355 <p>
1356 &copy; Copyright 2014 - 2019, British Columbia Institute of Technology.
1357 Last updated on Jan 16, 2019.
1358 </p>
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