182 lines
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182 lines
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<td><h1>CodeIgniter User Guide Version 1.7.3</h1></td>
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<a href="http://codeigniter.com/">CodeIgniter Home</a> ›
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<a href="../index.html">User Guide Home</a> ›
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Encryption Class
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<h1>Encryption Class</h1>
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<p>The Encryption Class provides two-way data encryption. It uses a scheme that pre-compiles
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the message using a randomly hashed bitwise XOR encoding scheme, which is then encrypted using
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the Mcrypt library. If Mcrypt is not available on your server the encoded message will
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still provide a reasonable degree of security for encrypted sessions or other such "light" purposes.
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If Mcrypt is available, you'll effectively end up with a double-encrypted message string, which should
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provide a very high degree of security.</p>
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<h2>Setting your Key</h2>
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<p>A <em>key</em> is a piece of information that controls the cryptographic process and permits an encrypted string to be decoded.
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In fact, the key you chose will provide the <strong>only</strong> means to decode data that was encrypted with that key,
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so not only must you choose the key carefully, you must never change it if you intend use it for persistent data.</p>
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<p>It goes without saying that you should guard your key carefully.
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Should someone gain access to your key, the data will be easily decoded. If your server is not totally under your control
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it's impossible to ensure key security so you may want to think carefully before using it for anything
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that requires high security, like storing credit card numbers.</p>
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<p>To take maximum advantage of the encryption algorithm, your key should be 32 characters in length (128 bits).
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The key should be as random a string as you can concoct, with numbers and uppercase and lowercase letters.
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Your key should <strong>not</strong> be a simple text string. In order to be cryptographically secure it
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needs to be as random as possible.</p>
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<p>Your key can be either stored in your <dfn>application/config/config.php</dfn>, or you can design your own
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storage mechanism and pass the key dynamically when encoding/decoding.</p>
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<p>To save your key to your <dfn>application/config/config.php</dfn>, open the file and set:</p>
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<code>$config['encryption_key'] = "YOUR KEY";</code>
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<h2>Message Length</h2>
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<p>It's important for you to know that the encoded messages the encryption function generates will be approximately 2.6 times longer than the original
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message. For example, if you encrypt the string "my super secret data", which is 21 characters in length, you'll end up
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with an encoded string that is roughly 55 characters (we say "roughly" because the encoded string length increments in
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64 bit clusters, so it's not exactly linear). Keep this information in mind when selecting your data storage mechanism. Cookies,
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for example, can only hold 4K of information.</p>
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<h2>Initializing the Class</h2>
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<p>Like most other classes in CodeIgniter, the Encryption class is initialized in your controller using the <dfn>$this->load->library</dfn> function:</p>
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<code>$this->load->library('encrypt');</code>
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<p>Once loaded, the Encrypt library object will be available using: <dfn>$this->encrypt</dfn></p>
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<h2>$this->encrypt->encode()</h2>
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<p>Performs the data encryption and returns it as a string. Example:</p>
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<code>
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$msg = 'My secret message';<br />
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<br />
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$encrypted_string = $this->encrypt->encode($msg);</code>
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<p>You can optionally pass your encryption key via the second parameter if you don't want to use the one in your config file:</p>
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<code>
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$msg = 'My secret message';<br />
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$key = 'super-secret-key';<br />
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<br />
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$encrypted_string = $this->encrypt->encode($msg, $key);</code>
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<h2>$this->encrypt->decode()</h2>
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<p>Decrypts an encoded string. Example:</p>
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<code>
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$encrypted_string = 'APANtByIGI1BpVXZTJgcsAG8GZl8pdwwa84';<br />
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<br />
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$plaintext_string = $this->encrypt->decode($encrypted_string);</code>
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<h2>$this->encrypt->set_cipher();</h2>
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<p>Permits you to set an Mcrypt cipher. By default it uses <samp>MCRYPT_RIJNDAEL_256</samp>. Example:</p>
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<code>$this->encrypt->set_cipher(MCRYPT_BLOWFISH);</code>
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<p>Please visit php.net for a list of <a href="http://php.net/mcrypt">available ciphers</a>.</p>
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<p>If you'd like to manually test whether your server supports Mcrypt you can use:</p>
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<code>echo ( ! function_exists('mcrypt_encrypt')) ? 'Nope' : 'Yup';</code>
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<h2>$this->encrypt->set_mode();</h2>
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<p>Permits you to set an Mcrypt mode. By default it uses <samp>MCRYPT_MODE_ECB</samp>. Example:</p>
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<code>$this->encrypt->set_mode(MCRYPT_MODE_CFB);</code>
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<p>Please visit php.net for a list of <a href="http://php.net/mcrypt">available modes</a>.</p>
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<h2>$this->encrypt->sha1();</h2>
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<p>SHA1 encoding function. Provide a string and it will return a 160 bit one way hash. Note: SHA1, just like MD5 is non-decodable. Example:</p>
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<code>$hash = $this->encrypt->sha1('Some string');</code>
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<p>Many PHP installations have SHA1 support by default so if all you need is to encode a hash it's simpler to use the native
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function:</p>
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<code>$hash = sha1('Some string');</code>
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<p>If your server does not support SHA1 you can use the provided function.</p>
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