PHP

The PHP language at first evolved without a written formal specification or standard, with the original implementation acting as the de facto standard that other implementations aimed to follow. Early history (1993 to 1997) PHP development began in 1993 which he used to maintain his personal homepage. He extended them to work with HTML forms and to communicate with databases, and called this implementation "Personal Home Page/Forms Interpreter" or PHP/FI. An example of the early PHP syntax: Hey, you are using Netscape! Sorry, that record does not exist Welcome ! You have credits left in your account. PHP/FI could be used to build simple, dynamic web applications. To accelerate bug reporting and improve the code, Lerdorf initially announced the release of PHP/FI as "Personal Home Page Tools (PHP Tools) version 1.0" on the Usenet discussion group comp.infosystems.www.authoring.cgi on 8 June 1995. This release included basic functionality such as Perl-like variables, form handling, and the ability to embed HTML. By this point, the syntax had changed to resemble that of Perl, but was simpler, more limited, and less consistent. A development team began to form and, after months of work and beta testing, officially released PHP/FI 2 in November 1997. The fact that PHP was not originally designed, but instead was developed organically has led to inconsistent naming of functions and inconsistent ordering of their parameters. In some cases, the function names were chosen to match the lower-level libraries which PHP was "wrapping", while in some very early versions of PHP the length of the function names was used internally as a hash function, so names were chosen to improve the distribution of hash values. PHP 3 and 4 (1998 to 2004) content management system. Zeev Suraski and Andi Gutmans rewrote the parser in 1997 and formed the base of PHP 3, changing the language's name to the recursive acronym PHP: Hypertext Preprocessor. Afterwards, public testing of PHP 3 began, and the official launch came in June 1998. Suraski and Gutmans then started a new rewrite of PHP's core, producing the Zend Engine in 1999. They also founded Zend Technologies in Ramat Gan, Israel. Early PHP 5 (2004 to 2006) On 1 July 2004, PHP 5.0 was released, powered by the new Zend Engine 2.0. PHP 5.1 and PHP 5.2 were released the following years, adding smaller improvements and new features, such as the PHP Data Objects (PDO) extension (which defines a lightweight and consistent interface for accessing databases) In 2008, PHP 5.x became the only stable version under development. Many high-profile open-source projects ceased to support PHP 4 in new code from February 5, 2008, because of the GoPHP5 initiative, provided by a consortium of PHP developers promoting the transition from PHP 4 to PHP 5. PHP 6 and Unicode PHP's native string functions worked only on raw bytes, making use with multibyte character encodings difficult. In 2005, a project headed by Andrei Zmievski was initiated to bring native Unicode support throughout PHP, by embedding the International Components for Unicode (ICU) library, and representing text strings as UTF-16 internally. Since this would cause major changes both to the internals of the language and to user code, it was planned to release this as version 6.0 of the language, along with other major features then in development. However, a shortage of developers who understood the necessary changes, and performance problems arising from conversion to and from UTF-16, which is rarely used in a web context, led to delays in the project. As a result, a PHP 5.3 release was created in 2009, and in March 2010, the project in its current form was officially abandoned, and a PHP 5.4 release was prepared to contain most remaining non-Unicode features from PHP 6. Initial hopes were that a new plan would be formed for Unicode integration, but by 2014 none had been adopted. Later PHP 5 (2009 to 2014) Because it contained features originally intended to be part of 6.0, PHP 5.3 was a significant release, adding support for namespaces, closures, late static binding, and many fixes and improvements to standard functions. With the Unicode branch officially abandoned, a new release process was adopted in 2011, planning a yearly release cycle, and a clear distinction between "feature releases" (x.y.z to x.y+1.z) and "major releases" (x.y.z to x+1.0.0). requiring Windows 32-bit compatibility mode while using Internet Information Services (IIS) on a 64-bit Windows platform. PHP version 5.5 made the 64-bit x86-64 builds available for Microsoft Windows. Official security support for PHP 5.6 ended on 31 December 2018. PHP 7.x (2015 to 2019) During 2014 and 2015, a new major PHP version was developed, PHP 7.0. The numbering of this version involved some debate among internal developers. While the PHP 6 Unicode experiments had never been released, several articles and book titles referenced the PHP 6 names, which might have caused confusion if a new release were to reuse the name. After a vote, the name PHP 7 was chosen. The foundation of PHP 7.0 was a PHP branch that was originally dubbed PHP next generation (phpng). It was written by Dmitry Stogov, Xinchen Hui and Nikita Popov, and aimed to optimize PHP performance by refactoring the Zend Engine while retaining near-complete language compatibility. By 14 July 2014, WordPress-based benchmarks, which served as the main benchmark suite for the phpng project, showed an almost 100% increase in performance. Changes from phpng make it easier to improve performance in future versions, as more compact data structures and other changes are seen as better suited for a successful migration to a just-in-time (JIT) compiler. Because of the significant changes, the reworked Zend Engine was called Zend Engine 3, succeeding Zend Engine 2 used in PHP 5.x. PHP 7.0 also included changes which were not backward compatible, as allowed for "major versions" under the versioning scheme agreed in 2011. a more predictable behavior of the foreach statement, and platform consistency of bitwise shifts Several unmaintained or deprecated server application programming interfaces (SAPIs) and extensions were removed from the PHP core, most notably the legacy mysql extension. Other legacy features were also removed, such as ASP-style delimiters <% and %> and <script language="php"> ... </script>. PHP 7.0 marked the beginning of an expansion in PHP's type system. In PHP 5.x, only function parameters could have type declarations, but this was extended to function return types in 7.0., and object properties in 7.4 The types expressible also expanded, with scalar types (integer, float, string, and boolean) in 7.0; type, nullable types, and return type. all in 7.1; and the type in 7.2 Other changes in this period aimed to add expressiveness to the language, such as the (null coalesce) and "spaceship" three-way comparison operators in 7.0; new syntax for array derefencing and catching multiple exception types in PHP 7.1; more flexible Heredoc and Nowdoc syntax in 7.3; and the null-coalescing assignment operator in 7.4. PHP 8.x (2020 onwards) PHP 8.0 was released on 26 November 2020, as a major version with breaking changes from previous versions. One of the most high-profile changes was the addition of a JIT compiler, which can provide substantial performance improvements for some use cases. Substantial improvements were expected more for mathematical-type operations than for common web-development use cases. Additionally, the performance advantage of the JIT compiler provides the potential to move some code from C to PHP. A significant addition to the language in 8.0 is attributes, which allow metadata to be added to program elements such as classes, methods, and parameters. in PHP 8.3, and the and attributes in PHP 8.5. A significant extension to the language's type system is the addition of composite types: union types in PHP 8.0 (e.g. meaning "either integer or string"), and referring to properties which have not been declared on the class. Release history Beginning on 28 June 2011, the PHP Development Team implemented a timeline for the release of new versions of PHP. Under this system, at least one release should occur every month. Once per year, a minor release should occur which may include new features. Every minor release should at least be supported for two years with security and bug fixes, followed by at least one year of only security fixes, for a total of a three-year release process for every minor release. No new features, unless small and self-contained, are to be introduced into a minor release during the three-year release process. A 2024 RFC extended the length of the security fix only period to two years, fixed all end of life dates to 31 December, and removed the exception that allowed for "small and self-contained" features to be introduced in patch versions. Those included the 9.7% of PHP websites using the even more outdated (discontinued for 7 years) and insecure PHP 5, released over two decades ago. == Mascot ==

The mascot of the PHP project is the elePHPant, a blue elephant with the PHP logo on its side, designed by Vincent Pontier in 1998. "The (PHP) letters were forming the shape of an elephant if viewed in a sideways angle." The elePHPant is sometimes differently coloured when in plush toy form. Many variations of this physical mascot have been made over the years. Only the elePHPants based on the original design by Vincent Pontier are considered official by the community. These are collectable and some of them are extremely rare. == Syntax ==

The following "Hello, World!" program is written in PHP code embedded in an HTML document: PHP "Hello, World!" program The PHP interpreter only executes PHP code within its delimiters. Anything outside its delimiters is not processed by PHP, although the non-PHP text can still be subject to control structures described in PHP code. is used to open and ?> to close PHP sections. A shorthand exists, which is a shorthand for . Conversely, there is no recommendation against the echo short tag . Prior to PHP 5.4.0, the short syntax for echo only works with the short_open_tag configuration setting enabled, while for PHP 5.4.0 and later it is always available. The purpose of delimiters is to separate PHP code from non-PHP content, such as JavaScript code or HTML markup. The first form of delimiters, and ?>, in XHTML and other XML documents, creates correctly formed XML processing instructions. This means that the resulting mixture of PHP code and other markup in the server-side file is itself well-formed XML. Variables are prefixed with a dollar symbol, and a type does not need to be specified in advance. PHP 5 introduced type declarations that allow functions to force their parameters to be objects of a specific class, arrays, interfaces or callback functions. However, before PHP 7, type declarations could not be used with scalar types such as integers or strings. PHP treats newlines as whitespace in the manner of a free-form language, and statements are terminated by a semicolon. PHP has three types of comments: /* */ marks block and inline comments; // or # are used for one-line comments. The echo statement is one of several keywords PHP provides to output text. Data types PHP is loosely typed. It stores integers in a platform-dependent range, either as a 32, 64 or 128-bit signed integer equivalent to the C-language long type. Unsigned integers are converted to signed values in certain situations, which is different behaviour to many other programming languages. Integer variables can be assigned using decimal (positive and negative), octal, hexadecimal, and binary notations. Floating-point numbers are also stored in a platform-specific range. They can be specified using floating-point notation, or two forms of scientific notation. PHP has a native Boolean type that is similar to the native Boolean types in Java and C++. Using the Boolean type conversion rules, non-zero values are interpreted as true and zero as false, as in Perl and C++. The Standard PHP Library (SPL) attempts to solve standard problems and implements efficient data access interfaces and classes. Functions PHP defines a large array of functions in the core language and many are also available in various extensions; these functions are well documented online PHP documentation. Functions may be defined inside code blocks, permitting a run-time decision as to whether or not a function should be defined. There is a function_exists function that determines whether a function with a given name has already been defined. Function calls must use parentheses, with the exception of zero-argument class constructor functions called with the PHP operator new, in which case parentheses are optional. Since PHP 4.0.1 create_function(), a thin wrapper around eval(), allowed normal PHP functions to be created during program execution; it was deprecated in PHP 7.2 and removed in PHP 8.0 in favor of syntax for anonymous functions or "closures" that can capture variables from the surrounding scope, which was added in PHP 5.3. Shorthand arrow syntax was added in PHP 7.4: function getAdder($x) { return fn($y) => $x + $y; } $adder = getAdder(8); echo $adder(2); // prints "10" In the example above, getAdder() function creates a closure using passed argument , which takes an additional argument , and returns the created closure to the caller. Such a function is a first-class object, meaning that it can be stored in a variable, passed as a parameter to other functions, etc. Unusually for a dynamically typed language, PHP supports type declarations on function parameters, which are enforced at runtime. This has been supported for classes and interfaces since PHP 5.0, for arrays since PHP 5.1, for "callables" since PHP 5.4, and scalar (integer, float, string and boolean) types since PHP 7.0. The drawback of this method was that code had to make heavy use of PHP's "reference" variables if it wanted to modify an object it was passed rather than creating a copy of it. In the new approach, objects are referenced by handle, and not by value. PHP 5 introduced private and protected member variables and methods, along with abstract classes, final classes, abstract methods, and final methods. It also introduced a standard way of declaring constructors and destructors, similar to that of other object-oriented languages such as C++, and a standard exception handling model. Furthermore, PHP 5 added interfaces and allowed for multiple interfaces to be implemented. There are special interfaces that allow objects to interact with the runtime system. Objects implementing ArrayAccess can be used with array syntax and objects implementing Iterator or IteratorAggregate can be used with the foreach language construct. There is no virtual table feature in the engine, so static variables are bound with a name instead of a reference at compile time. If the developer creates a copy of an object using the reserved word clone, the Zend engine will check whether a __clone() method has been defined. If not, it will call a default __clone() which will copy the object's properties. If a __clone() method is defined, then it will be responsible for setting the necessary properties in the created object. For convenience, the engine will supply a function that imports the properties of the source object, so the programmer can start with a by-value replica of the source object and only override properties that need to be changed. The visibility of PHP properties and methods is defined using the keywords public, private, and protected. The default is public, if only var is used; var is a synonym for public. Items declared public can be accessed everywhere. protected limits access to inherited classes (and to the class that defines the item). private limits visibility only to the class that defines the item. Objects of the same type have access to each other's private and protected members even though they are not the same instance. Example The following is a basic example of object-oriented programming in PHP 8: name = ucfirst(strtolower($name)); } public function greet(): string { return "Hello, my name is " . $this->name; } abstract public function job(): string; } class Student extends User { public function __construct(string $name, private string $course) { parent::__construct($name); } public function job(): string { return "I learn " . $this->course; } } class Teacher extends User { public function __construct(string $name, private array $teachingCourses) { parent::__construct($name); } public function job(): string { return "I teach " . implode(", ", $this->teachingCourses); } } $students = [ new Student("Alice", "Computer Science"), new Student("Bob", "Computer Science"), new Student("Charlie", "Business Studies"), ]; $teachers = [ new Teacher("Dan", ["Computer Science", "Information Security"]), new Teacher("Erin", ["Computer Science", "3D Graphics Programming"]), new Teacher("Frankie", ["Online Marketing", "Business Studies", "E-commerce"]), ]; foreach ([$students, $teachers] as $users) { echo $users[0]::class . "s:\n"; array_walk($users, function (User $user) { echo "{$user->greet()}, {$user->job()}\n"; }); } This program outputs the following: {{sxhl|2=output|Students: Hello, my name is Alice, I learn Computer Science Hello, my name is Bob, I learn Computer Science Hello, my name is Charlie, I learn Business Studies Teachers: Hello, my name is Dan, I teach Computer Science, Information Security Hello, my name is Erin, I teach Computer Science, 3D Graphics Programming Hello, my name is Frankie, I teach Online Marketing, Business Studies, E-commerce == Implementations ==

The only complete PHP implementation is the original, known simply as PHP. It is the most widely used and is powered by the Zend Engine. To disambiguate it from other implementations, it is sometimes unofficially called "Zend PHP". The Zend Engine compiles PHP source code on-the-fly into an internal format that it can execute, thus it works as an interpreter. It is also the "reference implementation" of PHP, as PHP has no formal specification, and so the semantics of Zend PHP define the semantics of PHP. Due to the complex and nuanced semantics of PHP, defined by how Zend works, it is difficult for competing implementations to offer complete compatibility. PHP's single-request-per-script-execution model, and the fact that the Zend Engine is an interpreter, leads to inefficiency; as a result, various products have been developed to help improve PHP performance. To speed up execution time and not have to compile the PHP source code every time the web page is accessed, PHP scripts can also be deployed in the PHP engine's internal format by using an opcode cache, which works by caching the compiled form of a PHP script (opcodes) in shared memory to avoid the overhead of parsing and compiling the code every time the script runs. An opcode cache, Zend Opcache, is built into PHP since version 5.5. Another example of a widely used opcode cache is the Alternative PHP Cache (APC), which is available as a PECL extension. While Zend PHP is still the most popular implementation, several other implementations have been developed. Some of these are compilers or support JIT compilation, and hence offer performance benefits over Zend PHP at the expense of lacking full PHP compatibility. Alternative implementations include the following: • HHVM (HipHop Virtual Machine) – developed at Facebook and available as open source, it converts PHP code into a high-level bytecode (commonly known as an intermediate language), which is then translated into x86-64 machine code dynamically at runtime by a just-in-time (JIT) compiler, resulting in up to 6× performance improvements. However, since version 7.2 Zend has outperformed HHVM, and HHVM 3.24 is the last version to officially support PHP. • HipHop – developed at Facebook and available as open source, it transforms the PHP scripts into C++ code and then compiles the resulting code, reducing the server load up to 50%. In early 2013, Facebook deprecated it in favour of HHVM due to multiple reasons, including deployment difficulties and lack of support for the whole PHP language, including the create_function() and eval() constructs. • Parrot – a virtual machine designed to run dynamic languages efficiently; the cross-translator Pipp transforms the PHP source code into the Parrot intermediate representation, which is then translated into the Parrot's bytecode and executed by the virtual machine. • PeachPie – a second-generation compiler to .NET Common Intermediate Language (CIL) bytecode, built on the Roslyn platform; successor of Phalanger, sharing several architectural components • Phalanger – compiles PHP into .Net Common Intermediate Language bytecode; predecessor of PeachPie • Quercus – compiles PHP into Java bytecode == Licensing ==

PHP is free software released under the PHP License, which is equivalent to the 3-clause BSD license. Versions prior to 8.6 were released under a more restrictive license, which stipulates that: This restriction on the use of "PHP" made the PHP License incompatible with the GNU General Public License (GPL), while the Zend License was incompatible due to an advertising clause similar to that of the original BSD license. == Development and community ==

PHP includes various free and open-source libraries in its source distribution or uses them in resulting PHP binary builds. PHP is fundamentally an Internet-aware system with built-in modules for accessing File Transfer Protocol (FTP) servers and many database servers, including PostgreSQL, MySQL, Microsoft SQL Server and SQLite (which is an embedded database), LDAP servers, and others. Numerous functions are familiar to C programmers, such as those in the stdio family, are available in standard PHP builds. PHP allows developers to write extensions in C to add functionality to the PHP language. PHP extensions can be compiled statically into PHP or loaded dynamically at runtime. Numerous extensions have been written to add support for the Windows API, process management on Unix-like operating systems, multibyte strings (Unicode), cURL, and several popular compression formats. Other PHP features made available through extensions include integration with Internet Relay Chat (IRC), dynamic generation of images and Adobe Flash content, PHP Data Objects (PDO) as an abstraction layer used for accessing databases, and even speech synthesis. Some of the language's core functions, such as those dealing with strings and arrays, are also implemented as extensions. The PHP Extension Community Library (PECL) project is a repository for extensions to the PHP language. Most of the community focuses on web development, and PHP running server side (though also serving JavaScript for the client side), and some exceptional uses are for e.g. standalone graphical applications (with PHP-GTK unmaintained now for over a decade), and even drone control. Some other projects, such as Zephir, provide the ability for PHP extensions to be created in a high-level language and compiled into native PHP extensions. Such an approach, instead of writing PHP extensions directly in C, simplifies the development of extensions and reduces the time required for programming and testing. By December 2018 the PHP Group consisted of ten people: Thies C. Arntzen, Stig Bakken, Shane Caraveo, Andi Gutmans, Rasmus Lerdorf, Sam Ruby, Sascha Schumann, Zeev Suraski, Jim Winstead, and Andrei Zmievski. Zend Technologies provides a PHP Certification based on PHP 8 exam (and previously based on PHP 7 and 5.5) for programmers to become certified PHP developers. == The PHP Foundation ==

On 26 November 2021, the JetBrains blog announced the creation of The PHP Foundation, which will sponsor the design and development of PHP. The foundation hires "Core Developers" to work on the PHP language's core repository. Roman Pronskiy, a member of the foundation's board, said that they aim to pay "market salaries" to developers. The response to the foundation has been largely positive. Germany's Sovereign Tech Fund provided more than 200,000 Euros to support the PHP Foundation. == Installation and configuration ==

There are two primary ways for adding support for PHP to a web server – as a native web server module, or as a CGI executable. PHP has a direct module interface called server application programming interface (SAPI), which is supported by many web servers including Apache HTTP Server, Microsoft IIS, Caddy (through FrankenPHP) and iPlanet Web Server. Some other web servers, such as OmniHTTPd, support the Internet Server Application Programming Interface (ISAPI), which is Microsoft's web server module interface. If PHP has no module support for a web server, it can always be used as a Common Gateway Interface (CGI) or FastCGI processor; in that case, the web server is configured to use PHP's CGI executable to process all requests to PHP files. PHP-FPM (FastCGI Process Manager) is an alternative FastCGI implementation for PHP, bundled with the official PHP distribution since version 5.3.3. When using PHP for command-line scripting, a PHP command-line interface (CLI) executable is needed. PHP supports a CLI server application programming interface (SAPI) since PHP 4.3.0. The main focus of this SAPI is developing shell applications using PHP. There are quite a few differences between the CLI SAPI and other SAPIs, although they do share many of the same behaviours. PHP has a direct module interface called SAPI for different web servers; PHP can also be used for writing desktop graphical user interface (GUI) applications, by using the or discontinued PHP-GTK extension. PHP-GTK is not included in the official PHP distribution, When PHP is installed and used in cloud environments, software development kits (SDKs) are provided for using cloud-specific features. For example: • Amazon Web Services provides the AWS SDK for PHP • Microsoft Azure can be used with the Windows Azure SDK for PHP. Numerous configuration options are supported, affecting both core PHP features and extensions. Configuration file php.ini is searched for in different locations, depending on the way PHP is used. The configuration file is split into various sections, while some of the configuration options can be also set within the web server configuration. == Use ==

PHP is a general-purpose scripting language that is especially suited to server-side web development, in which case PHP generally runs on a web server. Any PHP code in a requested file is executed by the PHP runtime, usually to create dynamic web page content or dynamic images used on websites or elsewhere. It can also be used for command-line scripting and client-side graphical user interface (GUI) applications. PHP can be deployed on most web servers, many operating systems and platforms, and can be used with many relational database management systems (RDBMS). Most web hosting providers support PHP for use by their clients. It is available free of charge, and the PHP Group provides the complete source code for users to build, customize and extend for their own use. (PHP and MySQL) Originally designed to create dynamic web pages, PHP now focuses mainly on server-side scripting, and it is similar to other server-side scripting languages that provide dynamic content from a web server to a client, such as Python, Microsoft's ASP.NET, Sun Microsystems' JavaServer Pages, and mod_perl. PHP has also attracted the development of many software frameworks that provide building blocks and a design structure to promote rapid application development (RAD). Some of these include PRADO, CakePHP, Symfony, CodeIgniter, Laravel, Yii Framework, Phalcon and Laminas, offering features similar to other web frameworks. The LAMP architecture has become popular in the web industry as a way of deploying web applications. PHP is commonly used as the P in this bundle alongside Linux, Apache and MySQL, although the P may also refer to Python, Perl, or some mix of the three. Similar packages, WAMP and MAMP, are also available for Windows and macOS, with the first letter standing for the respective operating system. Although both PHP and Apache are provided as part of the macOS base install, users of these packages seek a simpler installation mechanism that can be more easily kept up to date. For specific and more advanced usage scenarios, PHP offers a well-defined and documented way for writing custom extensions in C or C++. Besides extending the language itself in form of additional libraries, extensions are providing a way for improving execution speed where it is critical and there is room for improvements by using a true compiled language. PHP also offers well-defined ways for embedding itself into other software projects. That way PHP can be easily used as an internal scripting language for another project, also providing tight interfacing with the project's specific internal data structures. PHP received mixed reviews due to lacking support for multithreading at the core language level, though using threads is made possible by the "pthreads" PECL extension. A command line interface, php-cli, and two ActiveX Windows Script Host scripting engines for PHP have been produced. Popularity and usage statistics PHP is used for Web content management systems including MediaWiki, WordPress, Joomla, Drupal, Moodle, eZ Publish, eZ Platform, and SilverStripe. , PHP was used in more than 240 million websites (39% of those sampled) and was installed on 2.1 million web servers. (three months after PHP 8.5's release), PHP is used as the server-side programming language on 72% of websites where the language could be determined; PHP 8 is the most used version of the language with 56.6% of websites using PHP being on that version, while 34.3% use PHP 7, 9% use PHP 5 and 0.1% use PHP 4. == Security ==

In 2019, 11% of all vulnerabilities listed by the National Vulnerability Database were linked to PHP; historically, about 30% of all vulnerabilities listed since 1996 in this database are linked to PHP. Technical security flaws of the language itself or of its core libraries are not frequent (22 in 2009, about 1% of the total although PHP applies to about 20% of programs listed). Recognizing that programmers make mistakes, some languages include taint checking to automatically detect the lack of input validation which induces many issues. Such a feature has been proposed for PHP in the past, but either been rejected or the proposal abandoned. Third-party projects such as Suhosin and Snuffleupagus aim to remove or change dangerous parts of the language. Historically, old versions of PHP had some configuration parameters and default values for such runtime settings that made some PHP applications prone to security issues. Among these, magic_quotes_gpc and register_globals configuration directives were the best known; the latter made any URL parameters become PHP variables, opening a path for serious security vulnerabilities by allowing an attacker to set the value of any uninitialized global variable and interfere with the execution of a PHP script. Support for "magic quotes" and "register globals" settings has been deprecated since PHP 5.3.0, and removed from PHP 5.4.0. Another example for the potential runtime-settings vulnerability comes from failing to disable PHP execution (for example by using the engine configuration directive) for the directory where uploaded files are stored; enabling it can result in the execution of malicious code embedded within the uploaded files. The best practice is to either locate the image directory outside the document root available to the web server and serve it via an intermediary script or disable PHP execution for the directory which stores the uploaded files. Also, enabling the dynamic loading of PHP extensions (via enable_dl configuration directive) in a shared web hosting environment can lead to security issues. Implied type conversions that result in different values being treated as equal, sometimes against the programmer's intent, can lead to security issues. For example, the result of the comparison is true, because strings that are parsable as numbers are converted to numbers; in this case, the first compared value is treated as scientific notation having the value (), which is zero. Errors like this resulted in authentication vulnerabilities in Simple Machines Forum, Typo3 and phpBB when MD5 password hashes were compared. The recommended way is to use hash_equals() (for timing attack safety), strcmp or the identity operator (===), as results in false. In a 2013 analysis of over 170,000 website defacements, published by Zone-H, the most frequently (53%) used technique was the exploitation of file inclusion vulnerability, mostly related to insecure usage of the PHP language constructs include, require, and allow_url_fopen. Cryptographic security PHP includes rand() and mt_rand() functions which use a pseudorandom number generator, and are not cryptographically secure. As of version 8.1, the random_int() function is included, which uses a cryptographically secure source of randomness provided by the system. There are two attacks that can be performed over PHP entropy sources: "seed attack" and "state recovery attack". As of 2012, a $250 GPU can perform up to 2 MD5 calculations per second, while a $750 GPU can perform four times as many calculations at the same time. In combination with a "birthday attack" this can lead to serious security vulnerabilities. Long-term support The PHP development team provides official bug fixes for two years following release of each minor version followed by another two years where only security fixes are released.