本文实例讲述了php对文件进行hash运算的方法。分享给大家供大家参考。具体如下:
这段代码非常有用,如果你下载了一个文件,网站提供了hash结果,你可以对你下载下来的文件进行hash运算,以验证下载的文件是否正确。
<html> <head> <title>Hash (Check) Files</title> <style type='text/css'> #ok{color:green;} #nono{color:red;} </style> </head> <body> <?php if(!empty($_FILES)){ if ($_FILES["file"]["error"] > 0){ switch($_FILES["file"]["error"]){ case 1: echo "<b id='nono'>Error: The uploaded file exceeds the upload_max_filesize directive in php.ini</b><br>"; break; case 2: echo "<b id='nono'>Error: The uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form.</b><br>"; break; case 3: echo "<b id='nono'>Error: The uploaded file was only partially uploaded.</b><br>"; break; case 4: echo "<b id='nono'>Error: No file was uploaded.</b><br>"; break; case 6: echo "<b id='nono'>Error: Missing a temporary folder.</b><br>"; break; case 7: echo "<b id='nono'>Error: Failed to write file to disk.</b><br>"; break; case 8: echo "<b id='nono'>Error: A PHP extension stopped the file upload.</b><br>"; break; default: echo "<b id='nono'>Unknown error occured.</b><br>"; } } else { echo 'Upload: ' . $_FILES['file']['name'] . '<br>'; echo 'Type: ' . $_FILES['file']['type'] . '<br>'; echo 'Size: ' . (round($_FILES['file']['size'] / 1024, 2)) . ' Kb<br><br>'; if(array_search($_POST['algo'], hash_algos())===false){ echo 'Unknown hashing algorithm requested.<br>'; } else { echo 'Hashing Algorithm: '. $_POST['algo'] . '<br>'; $hash = hash_file($_POST['algo'], $_FILES['file']['tmp_name']); echo 'Calculated hash: ' . $hash . '<br>'; if($_POST['exphash']!=='none' && !empty($_POST['exphash'])){ echo 'Expected hash: ' . $_POST['exphash'] . '<br><br>'; echo ($hash==$_POST['exphash'])? '<b id="ok">Hash matched expected value.</b>' : '<b id="nono">Hash did not match expected value.</b>'; echo '<br>'; } } } ?> <br> <button onClick="document.location.reload(true)">Again</button> <?php } else { ?> <form action="" method="post" enctype="multipart/form-data"> <input type="hidden" name="exphash" value="none"> <label for="file">Filename:</label> <input type="file" name="file" id="file"> <input type="submit" name="submit" value="Submit" /><br> <label>Expected hash(optional): <input type="text" name="exphash" size="100"></label> <br><br>Choose an algorithm (This is the list of all the available algorithms in your php installation)<br> <?php foreach(hash_algos() as $algo){ if($algo=='md5'){ echo "<label><input type='radio' name='algo' value='$algo' checked='checked'>$algo</label><br>"; } else { echo "<label><input type='radio' name='algo' value='$algo'>$algo</label><br>"; } } ?> </form> <?php } ?> </body> </html>
希望本文所述对大家的php程序设计有所帮助。

In PHP, you can use session_status() or session_id() to check whether the session has started. 1) Use the session_status() function. If PHP_SESSION_ACTIVE is returned, the session has been started. 2) Use the session_id() function, if a non-empty string is returned, the session has been started. Both methods can effectively check the session state, and choosing which method to use depends on the PHP version and personal preferences.

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Managing concurrent session access in PHP can be done by the following methods: 1. Use the database to store session data, 2. Use Redis or Memcached, 3. Implement a session locking strategy. These methods help ensure data consistency and improve concurrency performance.

PHPsessionshaveseverallimitations:1)Storageconstraintscanleadtoperformanceissues;2)Securityvulnerabilitieslikesessionfixationattacksexist;3)Scalabilityischallengingduetoserver-specificstorage;4)Sessionexpirationmanagementcanbeproblematic;5)Datapersis

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Sessionlockingisatechniqueusedtoensureauser'ssessionremainsexclusivetooneuseratatime.Itiscrucialforpreventingdatacorruptionandsecuritybreachesinmulti-userapplications.Sessionlockingisimplementedusingserver-sidelockingmechanisms,suchasReentrantLockinJ

Alternatives to PHP sessions include Cookies, Token-based Authentication, Database-based Sessions, and Redis/Memcached. 1.Cookies manage sessions by storing data on the client, which is simple but low in security. 2.Token-based Authentication uses tokens to verify users, which is highly secure but requires additional logic. 3.Database-basedSessions stores data in the database, which has good scalability but may affect performance. 4. Redis/Memcached uses distributed cache to improve performance and scalability, but requires additional matching

Sessionhijacking refers to an attacker impersonating a user by obtaining the user's sessionID. Prevention methods include: 1) encrypting communication using HTTPS; 2) verifying the source of the sessionID; 3) using a secure sessionID generation algorithm; 4) regularly updating the sessionID.


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