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Essential PHP Security Paperback – October 20, 2005
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You've heard the nasty stories about PHP sites being wiped off the web by evil hackers? Sadly it's not scare-mongering as it does happen, and as much as we love PHP it needs proper security to keep your site safe from harm. Plenty of PHP books have the odd chapter on security but at last O'Reilly have published a whole volume dedicated to the cause, with all the code you'll need to keep everything in order. Each chapter covers a different aspect of the application, from form processing to database programming and session management. Written in a straight forward style, it's ideal for every PHP user, but at GBP20 you might expect a little more than just 100 pages." .NET, November 2005 "If you write PHP scripts, get a copy" - Alain Williams, news@UK, March 2006
About the Author
Chris Shiflett, an internationally recognized expert in the field of PHP security, is the founder and President of Brain Bulb, a PHP consultancy. Chris has been developing web applications with PHP for several years and regularly speaks at OSCON, ApacheCon, and PHP users conferences in North America. He is the author of the HTTP Developer's Handbook (Sams) and writes frequently about web application security. As an open source advocate, he maintains several open source projects and is a member of the PHP development team.
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Top Customer Reviews
The author is an internationally-known and accomplished expert on PHP security. He is the founder of the PHP Security Consortium, a group of volunteers who help educate the PHP community, and a well-known contributor to the PHP-general mail digest. The book is designed to provide security information and guidelines and explain the most common types of attacks and how to prevent or repel them.
"Essential PHP Security" is a slight volume of only 109 pages, including index. Shiflett wastes no time and immediately jumps into his topic, starting with his opinion on the use of the PHP concept of "register globals", a configuration setting which he recommends against using in favor of "superglobal arrays". He next turns to how to configure your web server setup to properly deal with error reporting, both for the developer's use and to prevent providing clues to any interloper trying to illegally access your site.
The balance of Chapter 1 itemizes general principles of Internet security: Defense in Depth - redundantly using more than one technique to secure your site; Least Privileges - writing code to minimize access to the least needed for any particular user's needs; Simple is Beautiful - the writing of clear, simple code, to make troubleshooting and auditing easier; and Minimize Exposure - taking steps to design and implement programs to eliminate or at least minimize display of sensitive data or code - don't even store credit card information unless absolutely necessary, he suggests.
Next, comes "Best Practices" - balancing risk vs. usability, keeping track of data, filtering of all input, escaping output, and in all cases, distinguishing between filtered and tainted data. These principles and practices are illustrated with short code snippets comparing insecure vs. more secure code.
The next seven chapters deal with specific elements of a website, the types of attacks that can occur with each, and tips and suggestions on how to deal with these attacks. These elements include vulnerabilities in forms and URLs, databases and SQL, sessions and cookies, PHP "include" files, files and commands, authentication and authorization, and shared hosting.
The author credibly describes by examples the types of attacks against forms and URLs - cross-site scripting, cross site request forgeries, spoofing of forms, and insecure Raw HTTP requests. Authentication attacks include dictionary attacks, password sniffing, replay attacks, and cookie stealing. For each, he briefly describes how the attacks work, shows examples of insecure code, and provides examples of secure code.
For each of the elements dealt with, the author follows the same model: describe briefly the types of attacks against each element, show conventionally-used insecure code, and show how to eliminate the insecure parts of the code. Most of the security defenses entail filtering data from outside sources, especially form input, email, and XML documents from other web applications. Other defense techniques include using SSL for encrypted data transmissions, strengthening identification methods, hard-coding file paths, and using token techniques in addition to PHP encryption functions. Interestingly, Schiflett believes it is impossible to achieve a high level of security in a shared hosting situation. He provides suggestions on what security measures will help the most.
What is most useful about this book is the aggregation in one place of descriptions of all of these security attacks, and vulnerabilities in PHP code, along with suggestions on dealing with them. The organization of the material is good, however. I believe the author falls short in his code examples. There appears to be a disconnect between the descriptive text (which is clear enough) and the examples, which are not, at least to me, a novice in PHP. I could not readily follow the detailed code segments, although I could understand in principle what was going on.
Some of the code segments were barely explained and some were inadequately explained. The concepts of the attacking techniques were understandable, but the detailed implementations were not. There are a small handful of illustrations, but I found them too simplistic and inadequate. To be fair, this may be a failure of the reviewer. More experienced PHP folks may not complain about the presentations. For them, this book gives them what they need to know about handling the security aspects of their applications, but my guess is that it is the less accomplished coders who need the most help (although those same people are probably writing the types of applications and sites least likely to be targeted by miscreants.)
There are three short appendices presenting suggestions on how to configure a PHP installation to minimize weaknesses, suggestions about avoiding certain powerful PHP functions, especially system commands, to minimize risk, and a short segment on cryptography features in PHP.
The author's blog ([...]) and PHP security website ([...]) are good sources of information on PHP security and web creation in general. With the wisdom hinted at via his websites, I looked forward to more in depth insights and specifics in his book. Unfortunately for Mr. Shiflett, writing a book is not like writing 'bites' for a blog or marketing yourself as experienced and knowledgable. This book reads like an anthology of blog articles and seminar presentations and that weakness kills what should otherwise really be an essential text.
As another helpful reviewer pointed out, this book is a not appropriate for new PHP programmers. That reviewer also noted that it is precisely new initiates to PHP that need these lessons the most. The protective measures suggested in the book are presented superficially. The author highlights the vulnerability, but then only hints at a protective measure by providing a code snip-it which totally lacks context. Most novice readers expect examples of how to apply and integrate the suggested technique effectively and efficiently within the basics they already know.
Mr. Shiflett writes in his acknowledgements, "Written during one of the busiest years of my life ... [the people at O'reilly] have gone out of their way to make the entire process fit around my writing style and busy schedule."
For a full price book, the author had room, but perhaps not the desire to provide more substance. Concise does not have to be superficial. The book's main content is 85 pages -- followed by three appendices between pages 87 and 103. The index runs between pages 105 and 109. Substantive implementation details are missing and should have been included.
For example, in chapter 1 and later in chapter 2, the author recommends filtering input by identifying input, filtering the input, and distinguishing between filtered and unfiltered (tainted) data. This recommendation is explicitly explained twice in the book and repeated throughout. If you expect any examples demonstrating this in practical use, there are none. If you expect a class that exemplifies a way you might integrate this technique with your exsisting code, there is none. In other words, if you want to learn even remotely by example, you may be disappointed by this book.
As a last note, Appendix C talks briefly about cryptography in PHP. Based on this book, cryptography does not appear to be one of the author's strong areas of knowledge. For new PHP programmers who also work with SQL, Mr. Shiflett gives you just enough information to frustrate you (at best -- or hang yourself at worst). The author lists a number of other books and websites about cryptography on the first page of the Appendix. That is his best advice. Also take a look at [...] as an information resource.
In sum, I don't argue with the value of the hints Mr. Shiflett provides in his book, but this book is weak on substance and does not provide the examples necessary to teach the reader that the suggestions are practical for real implementation. Perhaps instead of this book, the many authors of the "How to PHP and MySQL" clone books need to integrate and implement these protective measures in their texts right from the start. Unfortunately, Mr. Shiflett's book does not bridge the existing gap. If you buy this book, expect to be searching other books and the web for ways to effectively and efficiently perform the tasks the author recommends. If you already know how to implement the measures, you probably did not need this book in the first place.