How do I secure uploaded files?

I'm trying to build a document management system whereby persons can upload documents and have them stored on the server.
I'm using a simpy upload html form called test.html to upload the document and php in a file called uploader.php to store the upload file on the server.
I intend to save the path and filename of the document in a field of a documents table in a mySql database. I would use that information to later retrieve the file. However, my professor says that's not very secure because anyone who has the path and name can access the document.

How do I make the uploaded documents secure? Is there another way I can use so that I don't store the file address but still be able to retrieve documents?
<<<<<<<<< TEST.HTML >>>>>>>>>>>>>
<form enctype="multipart/form-data" action="uploader.php" method="POST">
<input type="hidden" name="MAX_FILE_SIZE" value="100000" />
Choose a file to upload: <input name="uploadedfile" type="file" /><br />
<input type="submit" value="Upload File" />
</form>
 
<<<<<<<<< UPLOADER.PHP >>>>>>>>>>>>>
<?php 
 
$target_path = "uploads/";
 
$target_path = $target_path . basename( $_FILES['uploadedfile']['name']); 
 
if(move_uploaded_file($_FILES['uploadedfile']['tmp_name'], $target_path)) {
    echo "The file ".  basename( $_FILES['uploadedfile']['name']). 
    " has been uploaded";
} else{
    echo "There was an error uploading the file, please try again!";
}
?>

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kgprettyAsked:
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Ray PaseurCommented:
One other note, you mentioned your "professor" so I need to ask if this is a schoolwork assignment.  By EE policy, we are not allowed to do those, so the only help we would be permitted to offer would be guidance.
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TagorCommented:
You can chmod the folder to prevent users from accessing the files. Or you could use an htaccess file to secure it with a password.
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kgprettyAuthor Commented:
How exactly can I "chmod the folder"??
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TagorCommented:
You can chmod the folder using FTP. Please see below for more information. Or search on 'chmod explained' or 'chmod tutorial'
Basically chmod (aka "permissions") is short for "change mode". On a linux server such as ours it basically is how you change permissions for files and directories that can be used by a script. And also what can be done with those files and directories. There are three parts to a chmod number. The first number is for "owner", the second number is for "group", and "others" is the third. Most scripts will give you the chmod settings that will be needed in either the "readme" for the script or in the script code itself. To give you an example of the meaning of owner, groups, and others, lets use the ZboX web forum script as an example. The definition of the three in the forum are: 
Owner: Me. I have access to everything in the script including admin 
areas. 
Group: Everyone who has registered for the forum. You can read and 
execute certain aspects of the script like posting. 
Others: This would be the unregistered "Guests" All they can do is read 
the forum. They can't post or interact in any way. 
Below are examples of the chmod numbers and their useage. 
777: all can read/write/exec
755: owner can do all, group/others can read/exec
644: owner can read/write, group/others can read only 
 
For Directories: 
777: all can read, write, search
755: owner can do all, others and group can only search 
Typical settings: 
cgi scripts: 755 
Data files: 666 
Configuration files: 644 (files not updated by scripts) 
Directories: 777 (with proper permissions on files in directory) 
Here's a security tip: chmod a script to 400 if you want to disable it. You can always chmod it to 755 when you want to run it again. 
Here's a handy little script that allows you to figure what chmod number you need: 
 
Source: http://zboxhosting.com/board/index.php/topic,79.0.html

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Ray PaseurCommented:
For a document management system you might want to use Google Docs.  If you are trying to write one yourself, consider using the data base to store the documents.  HTH, ~Ray
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kgprettyAuthor Commented:
Ray_Paseur, I am trying to implement a database to store the documents, didn't you read my question?
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kgprettyAuthor Commented:
I have phpMyAdmin set up on my computer and mySql. How do I implement chmod on my computer?
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Ray PaseurCommented:
I read your question, including this, "persons can upload documents and have them stored on the server" and between that and your professor's comment about security I concluded that you might be planning to place the documents in the server file system - ie, in a directory.  Of course you can do that, but if you want to secure the docs against prying eyes, you need a little more security.  A data base will provide that for you since it will not be directly accessible from outside the scripts running on your server.  If nobody but you can upload scripts to the server, you can control what the scripts will server up.

If you use a data base to store the docs, you do not need to worry about file and directory permissions because your scripts will provide the logic that implements the equivalent protections -- in other words, chmod is moot.  But if you want to learn about chmod, you can find it in the PHP man pages online here:
http://us2.php.net/manual/en/function.chmod.php -- be sure to read the notes as well as the description.

Best regards, ~Ray
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kgprettyAuthor Commented:
Thanx
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