Significant changes to the Encryption library

- Removed double-encoding with XOR scheme when Mcrypt is available.  Additional obfuscation was not significantly aiding security, and came at a very high performance cost.
- Changed the default encryption mode from ECB to CBC for much improved security
- Added an encode_from_legacy() method to allow re-encoding of permanent data that was originally encoded with the older methods.

3 files changed, 57 insertions, 6 deletions

diff --git a/user_guide/changelog.html b/user_guide/changelog.html
index d9c17ab76..c42bde01e 100644
--- a/user_guide/changelog.html
+++ b/user_guide/changelog.html
@@ -100,6 +100,10 @@ Hg Tag: </p>
 			<li>Added a second parameter (boolean) to <kbd>$this->zip->read_dir('/path/to/directory', FALSE)</kbd> to remove the preceding trail of empty folders when creating a Zip archive. This example would contain a zip with "directory" and all of its contents.</li>
 			<li>Added ability in the Image Library to handle PNG transparency for resize operations when using the GD lib.</li>
 			<li>Modified the Session class to prevent use if no encryption key is set in the config file.</li>
+			<li>Improved performance of the Encryption library on servers where Mcrypt is available.</li>
+			<li>Changed the default encryption mode in the Encryption library to CBC.</li>
+			<li>Added an <kbd>encode_from_legacy()</kbd> method to provide a way to transition encrypted data from CodeIgniter 1.x to CodeIgniter 2.x.
+				Please see the <a href="./installation/upgrade_200.html">upgrade instructions</a> for details.</li>
 		</ul>
 	</li>
 	<li>Database
diff --git a/user_guide/installation/upgrade_200.html b/user_guide/installation/upgrade_200.html
index f45875b3c..155df90d3 100644
--- a/user_guide/installation/upgrade_200.html
+++ b/user_guide/installation/upgrade_200.html
@@ -89,7 +89,20 @@ to
 
 </p>
 
-<h2>Step 3: Update your user guide</h2>
+<h2>Step 4: Update stored encrypted data</h2>
+
+<p class="important"><strong>Note:</strong> If your application does not use the Encryption library, does not store Encrypted data permanently, or is on an environment that does not support Mcrypt, you may skip this step.</p>
+
+<p>The Encryption library has had a number of improvements, some for encryption strength and some for performance, that has an unavoidable consequence of
+	making it no longer possible to decode encrypted data produced by the original version of this library.  To help with the transition, a new method has
+	been added, <kbd>encode_from_legacy()</kbd> that will decode the data with the original algorithm and return a re-encoded string using the improved methods.
+	This will enable you to easily replace stale encrypted data with fresh in your applications, either on the fly or en masse.</p>
+	
+<p>Please read <a href="../libraries/encryption.html#legacy">how to use this method</a> in the Encryption library documentation.</p>
+
+</p>
+
+<h2>Step 5: Update your user guide</h2>
 <p>Please replace your local copy of the user guide with the new version, including the image files.</p>
 
 </div>
diff --git a/user_guide/libraries/encryption.html b/user_guide/libraries/encryption.html
index dac1db911..fbffd63c6 100644
--- a/user_guide/libraries/encryption.html
+++ b/user_guide/libraries/encryption.html
@@ -58,12 +58,11 @@ Encryption Class
 
 <h1>Encryption Class</h1>
 
-<p>The Encryption Class provides two-way data encryption.  It uses a scheme that pre-compiles
-the message using a randomly hashed bitwise XOR encoding scheme, which is then encrypted using
+<p>The Encryption Class provides two-way data encryption.  It uses a scheme that either compiles
+the message using a randomly hashed bitwise XOR encoding scheme, or is encrypted using
 the Mcrypt library.  If Mcrypt is not available on your server the encoded message will
 still provide a reasonable degree of security for encrypted sessions or other such "light" purposes.
-If Mcrypt is available, you'll effectively end up with a double-encrypted message string, which should
-provide a very high degree of security.</p>
+If Mcrypt is available, you'll be provided with a high degree of security appropriate for storage.</p>
 
 
 <h2>Setting your Key</h2>
@@ -153,7 +152,7 @@ $encrypted_string = $this->encrypt->decode($msg, $key);</code>
 
 <h2>$this->encrypt->set_mode();</h2>
 
-<p>Permits you to set an Mcrypt mode.  By default it uses <samp>MCRYPT_MODE_ECB</samp>.  Example:</p>
+<p>Permits you to set an Mcrypt mode.  By default it uses <samp>MCRYPT_MODE_CBC</samp>.  Example:</p>
 <code>$this->encrypt->set_mode(MCRYPT_MODE_CFB);</code>
 <p>Please visit php.net for a list of  <a href="http://php.net/mcrypt">available modes</a>.</p>
 
@@ -169,7 +168,42 @@ function:</p>
 
 <p>If your server does not support SHA1 you can use the provided function.</p>
 
+<h2 id="legacy">$this->encrypt->encode_from_legacy(<kbd>$orig_data</kbd>, <kbd>$legacy_mode</kbd> = MCRYPT_MODE_ECB, <kbd>$key</kbd> = '');</h2>
+<p>Enables you to re-encode data that was originally encrypted with CodeIgniter 1.x to be compatible with the Encryption library in CodeIgniter 2.x.  It is only
+	necessary to use this method if you have encrypted data stored permanently such as in a file or database and are on a server that supports Mcrypt.  "Light" use encryption
+	such as encrypted session data or transitory encrypted flashdata require no intervention on your part.  However, existing encrypted Sessions will be
+	destroyed since data encrypted prior to 2.x will not be decoded.</p>
 
+<p class="important"><strong>Why only a method to re-encode the data instead of maintaining legacy methods for both encoding and decoding?</strong>  The algorithms in
+	the Encryption library have improved in CodeIgniter 2.x	both for performance and security, and we do not wish to encourage continued use of the older methods.
+	You can of course extend the Encryption library if you wish and replace the new methods with the old and retain seamless compatibility with CodeIgniter 1.x
+	encrypted data, but this a decision that a developer should make cautiously and deliberately, if at all.</p>
+
+<code>$new_data = $this->encrypt->encode_from_legacy(<kbd>$old_encrypted_string</kbd>);</code>
+
+<table cellpadding="0" cellspacing="1" border="0" style="width:100%" class="tableborder">
+<tr>
+	<th>Parameter</th>
+	<th>Default</th>
+	<th>Description</th>
+</tr>
+<tr>
+	<td class="td"><strong>$orig_data</strong></td>
+	<td class="td">n/a</td>
+	<td class="td">The original encrypted data from CodeIgniter 1.x's Encryption library</td>
+</tr>
+<tr>
+	<td class="td"><strong>$legacy_mode</strong></td>
+	<td class="td">MCRYPT_MODE_ECB</td>
+	<td class="td">The Mcrypt mode that was used to generate the original encrypted data.  CodeIgniter 1.x's default was MCRYPT_MODE_ECB, and it will
+		assume that to be the case unless overridden by this parameter.</td>
+</tr>
+<tr>
+	<td class="td"><strong>$key</strong></td>
+	<td class="td">n/a</td>
+	<td class="td">The encryption key.  This it typically specified in your config file as outlined above.</td>
+</tr>
+</table>
 
 </div>
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