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admin10c3f412006-10-08 07:21:12 +0000[diff] [blame]50Encryption Class
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admin10c3f412006-10-08 07:21:12 +0000[diff] [blame]64<h1>Encryption Class</h1>
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]65
admin10c3f412006-10-08 07:21:12 +0000[diff] [blame]66<p>The Encryption Class provides two-way data encryption. It uses a scheme that pre-compiles
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]67the message using a randomly hashed bitwise XOR encoding scheme, which is then encrypted using
68the Mcrypt library. If Mcrypt is not available on your server the encoded message will
admine334c472006-10-21 19:44:22 +0000[diff] [blame]69still provide a reasonable degree of security for encrypted sessions or other such "light" purposes.
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]70If Mcrypt is available, you'll effectively end up with a double-encrypted message string, which should
71provide a very high degree of security.</p>
72
73
74<h2>Setting your Key</h2>
75
admine334c472006-10-21 19:44:22 +0000[diff] [blame]76<p>A <em>key</em> is a piece of information that controls the cryptographic process and permits an encrypted string to be decoded.
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]77In fact, the key you chose will provide the <strong>only</strong> means to decode data that was encrypted with that key,
admine7e1dcd2006-10-21 18:04:01 +0000[diff] [blame]78so not only must you chose the key carefully, you must never change it if you intend use it for persistent data.</p>
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]79
80<p>It goes without saying that you should guard your key carefully.
81Should someone gain access to your key, the data will be easily decoded. If your server is not totally under your control
82it's impossible to ensure key security so you may want to think carefully before using it for anything
83that requires high security, like storing credit card numbers.</p>
84
admine334c472006-10-21 19:44:22 +0000[diff] [blame]85<p>To take maximum advantage of the encryption algorithm, your key should be 32 characters in length (128 bits).
86The key should be as random a string as you can concoct, with numbers and uppercase and lowercase letters.
87Your key should <strong>not</strong> be a simple text string. In order to be cryptographically secure it
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]88needs to be as random as possible.</p>
89
admine334c472006-10-21 19:44:22 +0000[diff] [blame]90<p>Your key can be either stored in your <dfn>application/config/config.php</dfn>, or you can design your own
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]91storage mechanism and pass the key dynamically when encoding/decoding.</p>
92
93<p>To save your key to your <dfn>application/config/config.php</dfn>, open the file and set:</p>
94<code>$config['encryption_key'] = "YOUR KEY";</code>
95
96
97<h2>Message Length</h2>
98
admine334c472006-10-21 19:44:22 +0000[diff] [blame]99<p>It's important for you to know that the encoded messages the encryption function generates will be approximately 2.6 times longer than the original
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]100message. For example, if you encrypt the string "my super secret data", which is 21 characters in length, you'll end up
101with an encoded string that is roughly 55 characters (we say "roughly" because the encoded string length increments in
10264 bit clusters, so it's not exactly linear). Keep this information in mind when selecting your data storage mechanism. Cookies,
103for example, can only hold 4K of information.</p>
104
105
106<h2>Initializing the Class</h2>
107
admin10c3f412006-10-08 07:21:12 +0000[diff] [blame]108<p>Like most other classes in Code Igniter, the Encryption class is initialized in your controller using the <dfn>$this->load->library</dfn> function:</p>
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]109
110<code>$this->load->library('encrypt');</code>
111<p>Once loaded, the Encrypt library object will be available using: <dfn>$this->encrypt</dfn></p>
112
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]113
114<h2>$this->encrypt->encode()</h2>
115
116<p>Performs the data encryption and returns it as a string. Example:</p>
117<code>
118$msg = 'My secret message';<br />
119<br />
120$encrypted_string = $this->encrypt->encode($msg);</code>
121
122<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>
123
124<code>
125$msg = 'My secret message';<br />
126$key = 'super-secret-key';<br />
127<br />
128$encrypted_string = $this->encrypt->encode($msg, $key);</code>
129
130
131<h2>$this->encrypt->decode()</h2>
132
133<p>Decrypts an encoded string. Example:</p>
134
135<code>
136$encrypted_string = 'APANtByIGI1BpVXZTJgcsAG8GZl8pdwwa84';<br />
137<br />
138$plaintext_string = $this->encrypt->decode($encrypted_string);</code>
139
140
admin9fa00372006-10-12 18:20:13 +0000[diff] [blame]141<h2>$this->encrypt->set_cipher();</h2>
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]142
admin9fa00372006-10-12 18:20:13 +0000[diff] [blame]143<p>Permits you to set an Mcrypt cipher. By default it uses <samp>MCRYPT_RIJNDAEL_256</samp>. Example:
144<code>$this->encrypt->set_cipher('MCRYPT_BLOWFISH');</code>
145<p>Please visit php.net for a list of <a href="http://php.net/mcrypt">available ciphers</a>.</p>
adminb0dd10f2006-08-25 17:25:49 +0000[diff] [blame]146
147<p>If you'd like to manually test whether your server supports Mcrypt you can use:</p>
148<code>echo ( ! function_exists('mcrypt_encrypt')) ? 'Nope' : 'Yup';</code>
149
150
151<h2>$this->encrypt->set_mode();</h2>
152
153<p>Permits you to set an Mcrypt mode. By default it uses <samp>MCRYPT_MODE_ECB</samp>. Example:
154<code>$this->encrypt->set_mode('MCRYPT_MODE_CFB');</code>
155<p>Please visit php.net for a list of <a href="http://php.net/mcrypt">available modes</a>.</p>
156
157
158<h2>$this->encrypt->sha1();</h2>
159<p>SHA1 encoding function. Provide a string and it will return a 160 bit one way hash. Note: SHA1, just like MD5 is non-decodable. Example:</p>
160<code>$hash = $this->encrypt->sha1('Some string');</code>
161
162<p>Many PHP installations have SHA1 support by default so if all you need is to encode a hash it's simpler to use the native
163function:</p>
164
165<code>$hash = sha1('Some string');</code>
166
167<p>If your server does not support SHA1 you can use the provided function.</p>
168
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