Redevelopment

For a recent project I needed to use RSA encryption to encrypt some sensitive data that was being sent from a client to a (JSON) service. Both the client and the service are written in PHP using Zend Framework, so the obvious place to look for classes implementing this functionality is… well the Zend Framework library of course.

I was happily surprised finding the class Zend_Crypt_Rsa in the Crypt folder of the Zend Framework. When I wanted to check the online documentation at http://framework.zend.com/manual/en I was less happy, because it turns out there is no documentation for this class. Luckily it’s really not that hard to use. If you check out the code of the class itself it’s pretty self explanatory. However to save someone else some time it might be useful to post the steps I took to get it working, so here we go.

1. First of all you will need to have OpenSSL installed and the openssl PHP extension loaded, because the Zend_Crypt_Rsa class is dependent on it.

2. You have to generate the private and public keys that you’re going to use for the encryption (public key) and decryption (private key). You do this using the ssh-keygen command:

bender:~ ruben$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/ruben/.ssh/id_rsa): id_rsa
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in id_rsa.
Your public key has been saved in id_rsa.pub.
The key fingerprint is:
e4:ec:fc:ae:b4:8e:6a:b0:85:6e:1f:72:58:56:ec:1e ruben@bender
The key's randomart image is:
+--[ RSA 2048]----+
|                 |
|     .           |
|      o .        |
|     o +         |
|   .o E S        |
|  o+.. +         |
| .o+o . +        |
|  +o.. o o       |
| . oo...+oo      |
+-----------------+
bender:~ ruben$

As you can see you have to specify a passphrase, note that this should be longer than 4 characters.
At this point you should have two files: id_rsa – the private key and id_rsa.pub – the public key.

3. Now move those two files to a folder inside your project, *outside* of the webroot(!), for instance “keys”.

4. Now you’re ready to encrypt something. Here’s a small example:

What this does is encrypt the word ‘secretword’ using your public key (located at ../keys/id_rsa). Note that the passPhrase parameter of the constructor should match the passphrase you used to create the keys. The output of the encryption will be in Base64 format. You can also choose to use binary (Zend_Crypt_Rsa::BINARY), but that’s less convenient for transferring purposes.

5. Decrypting is just as simple:

In this case the variable $encryptedString contains a Base64 string representing a previously encrypted string.

That’s all there’s to it, pretty easy right?

In many webprojects I need to parse XML files of different kinds and shapes. PHP offers the DOMDocument class and the SimpleXML extension to read, parse, query and create XML documents. I personally prefer using the DOMDocument class hierarchy to SimpleXML, because it’s more powerful and offers more functionality especially when it comes to creating XML documents.

To show some possibilities of those classes I will demonstrate how to use them to parse Excel XML data. Here’s a screenshot of a small demo Excel workbook (a fictive pricelist):

You can save any Excel file in Excel XML format using Save As… and selecting XML Spreadsheet 2003 (*.xml):

After saving it to an XML file, the XML will look like this:

I collapsed the first few elements, because I’m going to focus on parsing the actual Worksheet data in this example.
So lets say you’re interested in parsing the cell data of this Excel sheet. If you only want to perform simple queries on your XML document the DOMDocument methods will suffice. In this case where you only want to get all Cell elements you could use the getElementsByTagName method, i.e.:

$xmlFile = 'pricelist.xml';
$domDoc = new DOMDocument();
$domDoc->load($xmlFile);
$cells = $domDoc->getElementsByTagName('Cell');

After this the variable $cells will contain a DOMNodeList object, which is just a list of DOMNode objects which you can traverse.

If you want to perform more complicated queries on your XML document you could use XPath. XPath is an XML query language with a simple syntax and relatively powerful possibilities.

In PHP’s DOM class hierarchy we have the class DOMXPath to perform XPath queries. For example to do the same as the getElementsByTagName code above, we can perform this XPath query: //ss:Data
The double slash in that query means that it doesn’t matter where in the document the element ss:Data is located. This will simply fetch every single ss:Data element in the document. If you want to get specific elements, starting at the document root, you should use single slash syntax like this: /ss:Workbook/ss:Worksheet/ss:Table/ss:Row/ss:Cell/ss:Data.

Also note that I’m using the ss: prefix to tell XPath to look for elements in that namespace, which is the microsoft spreadsheet namespace in this case.

Executing a query using DOMXPath would go like this:

$xmlFile = 'pricelist.xml';
$domDoc = new DOMDocument();
$domDoc->load($xmlFile);
$xpath = new DOMXpath($domDoc);
 
$dataElems = $xpath->query('//ss:Data');
 
foreach ($dataElems as $curElem)
{
	echo $curElem->nodeValue . "\n";
}

The cool thing about XPath is that you can use filterqueries that are quite advanced. You can specify extra elementfilters in square brackets. For example to get all Row elements with exactly 3 Cell elements that contain a Data element in the above Excel XML, you could use a count filter like this:
//ss:Row[count(ss:Cell/ss:Data)=3]

$xmlFile = 'pricelist.xml';
$domDoc = new DOMDocument();
$domDoc->load($xmlFile);
$xpath = new DOMXpath($domDoc);
 
$rows = $xpath->query('//ss:Row[count(ss:Cell/ss:Data)=3]');
 
foreach ($rows as $curRow)
{
	// iterate through Cell elems
	foreach ($curRow->childNodes as $curCell)
	{
		// ...
	}
}

Basically these classes make parsing XML a walk in the park, that is if you know how to use them. I hope this brief introduction will help you to get you going.

• Marina posted on September 18, 2011
  You have really interesting blog, keep up posting such informative posts!

The new version (1.0.1) of the php_solr extension is available for download at: http://pecl.php.net/package/solr. Unfortunately there are no binaries available for Windows, so I decided to build it myself. I compiled a 32-bit non-threadsafe version for PHP 5.3.9, so if you are interested you can download it here: php_solr 1.0.1

Simply unpack it and put it in your php ext folder. Then add an extension=php_solr.dll in your php.ini and you are good to go.