The md5() function uses MD5, a third-pary hash algorithm often used for creating digital signatures. HD5 is considered to be a one-way hashing algorithm, which means there is no practical way to dehash data that has been hashed using md5().

Prototype:
string md5(string str)

Example:
<?php
   $val="secret";
  $hash_val=md5($val);
   echo $hash_val;
?>

1. Zend Framework: It is an open source project fostered by the prominent PHP product and services provider Zend Technologies.
2. CakePHP Framework: It most closely corresponds to Rails, and indeed its developers readily mention that the project was originally inspired by the breakout framework. 
3. Solar Framework: An acronym for Simple Object Libray and Application Repository for PHP5, offers an extraordinary number of classes for facilitating rapid application development.
4. Symfony Framework: It is the brainchild of Fabien Potencier, founder of the French Web development firm Senso.

bool move_uploaded_file ( string $filename , string $destination )
bool copy ( string $source , string $dest [, resource $context ] )

Data Encryption: Data encryption can be defined as the translation of data into a format that is intended to be unreadable by anyone except the intended party. The intended party can then decode, or decrypt, the encrypted data through the use of some secret, typically a secret key or password.

HTTP is called stateless protocol because each request is processed without any knowledge of any prior or future requests.