PHP encryption symmetric program example using crypt to store password in a text file

September 8, 2019

Q. Symmetric encryption is a type of encryption where the same key is used to encrypt and decrypt the message. Can you explain how do I use symmetric encryption under PHP to store password in a text file and authenticate the user?

A. Symmetric encryption differs from asymmetric (also known as public-key) encryption, which uses one key to encrypt a message and another to decrypt the message.

PHP crypt() will return an encrypted string using the standard Unix DES-based encryption algorithm or alternative algorithms that may be available on the system. Arguments are a string to be encrypted and an optional salt string to base the encryption on. See the Unix man page for your crypt function for more information.

string crypt ( string $str [, string $salt] )

Consider following example.
$en_password : Stores encrypted password. You need to store this in database or flat text file.
$userPasswordInput : Holds user provided / supplied password via HTML page

If command is use to check encrypted password (hash) with user supplied password.

//Standard DES-based encryption with a two character salt called 'ge'
$en_password = crypt('secrete','ge');

if (crypt($userPasswordInput, $en_password) == $en_password) {
   echo "Password verified, you can login!";

PHP Function to write / store password to a file called /home/secure/.password

function updateAdminLoginPassword($new){
  //This is Blowfish encryption with a sixteen character salt starting with or $2a$
  $encryptedPassword = crypt($new, '$2a$didIL...fpSd78..$');
  // Open the file and erase the contents if any
  $fp = fopen("/home/secure/.password", "w");
  // Write the data to the file
  fwrite($fp, $Password);
  // Close the file
  echo '<h3>Password has been updated!<h3>';
  echo '<SCRIPT>alert('Password changed! You must login again to use new password');</SCRIPT>';
  /* resetSession(); */

Function to verify a password (note we are using hash in both functions $2a$didIL…fpSd78..$):

function verifyPassword($password)
 $username= "admin"; 
// read encrypted password
 $fp = fopen("/home/secure/.password", "r");
 while ( $line = fgets($fp, 1000) ) { $encryptedpasswd=$line; }
 if ( $_POST["username"] == $username && (crypt($password,'$2a$didIL...fpSd78..$') ==  $encryptedpasswd) )
 { // allow login
		session_start(); //Initialize session data
                //store user login name and password
		$_SESSION['user'] = $username;
                $_SESSION['pwd'] = $encryptedpasswd;  
                // display main menu
		header( "Location: /welcome.php" );
 {       // password is not correct or session expired due to password change
	header( "Location: /login.php?sessionnotfound=1" );

Above examples just provides you idea about php password encryptions and hash. You must consider other factors such as SSL http session, MD5 password / hash and mysql database to store password has etc.

Further readings:

Posted by: SXI ADMIN

The author is the creator of SXI LLC and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

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