PHP: Utility class for hashing password securely

PasswordHash.class.php

<?php 

/**
 *  Utility class for hashing password securely
 *  (source material from Net Tuts+)
 *
 *  @author Niko Heikkilä
 *  @version 1.0
 */

class PasswordHash
{

    /**
     *  @var string $alg   Algorithm for crypting
     *  @var string $cost  The cost parameter
     */

    private static $alg  = '$2a';
    private static $cost = '$10';

    /**
     *  Internal function for creating 22-character long salt
     *
     *  @return string
     */

    public static function uniqueSalt()
    {
        $salt = sha1( mt_rand() );
        return substr( $salt, 0, 22 );
    }

    /**
     *  Generate a hash
     *
     *  @param string $password Password to hash
     *  @return string
     */

    public static function hash( $password )
    {
        $full_salt = self::$alg . self::$cost . '$' . self::uniqueSalt();
        return crypt( $password, $full_salt );
    }

    /**
     *  Compare password against a hash
     *
     *  @param string $hash Hash value
     *  @param string $password Password from input 
     *  @return boolean
     */

    public static function checkPassword( $hash, $password )
    {
        $full_salt = substr( $hash, 0, 29 );
        $new_hash = crypt( $password, $full_salt );

        /* TRUE if match */
        return ( $hash === $new_hash );
    }

}
/* End of file PasswordHash.class.php */