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How do you prevent multiple clients from using the same session ID? I'm asking this because I want to add an extra layer of security to prevent session hijacking on my website. If a hacker somehow figures out another user's session ID and makes requests with that SID, how can I detect that there are different clients sharing a single SID on the server and then reject the hijack attempt?
EDIT
I have accepted Gumbo's answer after careful consideration because I've come to the realization that what I'm asking for is impossible due to the restrictions of a stateless HTTP protocol. I forgot about what is perhaps the most fundamental principle of HTTP, and now that I think about this question seems a bit trivial.
Let me elaborate what I mean:
After User A logs in on example.com, he is given some random session ID, for simplicity's sake, let it be 'abc123'. This session ID is stored as a cookie on the client side and is validated with a server-side session to ensure the user who logged in remains logged in as he moves from one webpage to another. This cookie of course would not need to exist if HTTP were not stateless. For that reason, if User B steals User A's SID, and creates a cookie on his computer with the value 'abc123', he would have successfully hijacked User A's session, but there is simply no way for the server to legitimately recognize that User B's request is any different from User A's requests, and therefore the server has no reason to reject any request. Even if we were to list the sessions that were already active on the server and try to see if someone is accessing a session that is already active, how can we determine that it is another user who is accessing the session illegitimately and not the same user who is already logged in with a session ID, but simply trying to make another request with it (ie navigate to a different webpage). We can't. Checking the user agent? Can be spoofed - but good as a Defense in Depth measure nevertheless. IP Address? Can change for legitimate reasons - but instead of not checking for the IP address at all, I suggest checking something like the first two octets of the IP, as even a user on a data plan network who constantly has a changing IP for perfectly legitimate reasons would only usually have the last two octets of their IP change.
In consclusion, it is the stateless HTTP that condemns us to never being able to fully protect our websites from session hijacking, but good practices (like the ones Gumbo has provided) will be good enough to prevent a good majority of session attacks. Trying to protect sessions from hijacking by denying multiple requests of the same SID is therefore simply ludicrous, and would defeat the whole purpose of sessions.
Unfortunately, there is no effective way to unmistakably identify a request that originates from an attacker in opposite to a genuine request. Because most properties that counter measures check like the IP address or user agent characteristics are either not reliable (IP address might change among multiple requests) or can be forged easily (e. g. User-Agent request header) and thus can yield unwanted false positives (i. e. genuine user switched IP address) or false negatives (i. e. attacker was able to successfully forge request with same User-Agent).
That’s why the best method to prevent session hijacking is to make sure an attacker cannot find out another user’s session ID. This means you should design your application and its session management that (1) an attacker cannot guess a valid session ID by using enough entropy, and (2) that there is no other way for an attacker to obtain a valid session ID by known attacks/vulerabilities like sniffing the network communication, Cross-Site Scripting, leakage through Referer, etc.
That said, you should:
use enough random input for generating the session ID (see session.entropy_file, session.entropy_length, and session.hash_function)
use HTTPS to protect the session ID during transmission
store the session ID in a cookie and not in the URL to avoid leakage though Referer (see session.use_only_cookies)
set the cookie with the HttpOnly and Secure attributes to forbid access via JavaScript (in case of XSS vulnerabilities) and to forbid transmission via insecure channel (see session.cookie_httponly and session.cookie_secure)
Besides that, you should also regenerate the session ID while invalidating the old one (see session_regenerate_id function) after certain session state changes (e. g. confirmation of authenticity after login or change of authorization/privileges) and you can additionally do this periodically to reduce the time span for a successful session hijacking attack.
Can we do something like this.
Store session id in database.
Also store the Ip address and the HTTP_USER_AGENT for that session id.
Now when a request comes to the server containing that matching session id, Check from which agent and ip it is coming from in your script.
Can make this funda work by make common function or class for session so that every request is verified before it is processed. It would hardly take some micro seconds. But, If many users are visiting your site and you have huge database of sessions, then this might be little performance issue. But, It would surely be very secure compared o other methods like
=> Using regenerating sessions.
In regenerating session ids, there is again little chance of session hijacking.
suppose, user's session id is copied and that user is not working or active for sometime and no request is made to server with old session id asking to regenerate new one. Then In case session id is hijacked, hacker will use that session id and make request to server with that id, then server will respond back with regenerated session id and so that hacker can go on using the services. Actual user will no longer be able to operate because he is unknown of what the regenerated id is and what request session id is to be passed in request. Completely Gone.
Please correct me if i m wrong somewhere.
There are lots of standard defenses against session hijacking. One of them is to match each session to a single IP address.
Other schemes may use an HMAC generated from:
the network address of the client's IP
the user-agent header sent by the client
the SID
a secret key stored on the server
The reason only the network address of the IP is used is in case the user is behind a public proxy, in which case their IP address can change with each request, but the network address remains the same.
Of course, to truly be secure, you really ought to force SSL for all requests so that the SID can't be intercepted by would-be attackers in the first place. But not all sites do this (::cough:: Stack Overflow ::cough::).
Session hijacking is a serious threat, it has to handle by using a secure socket layer for advanced application which involves transactions or by using simple techniques like using cookies, session timeouts and regenerates id etc as explained above.
When the internet was born, HTTP communications were designed to be stateless; that is, a connection between two entities exists only for the brief period of time required for a request to be sent to the server, and the resulting response passed back to the client.
Here are a few methods which hackers follow to hijack the session
Network Eavesdropping
Unwitting Exposure
Forwarding, Proxies, and Phishing
Reverse Proxies
Always recommend SSL Secure Sockets Layer
Use cookies also to following ini_set() directives at the start of your scripts, in order to override any global settings in php.ini:
ini_set( 'session.use_only_cookies', TRUE );
ini_set( 'session.use_trans_sid', FALSE );
Use Session Timeouts and Session Regenerate ID
<?php
// regenerate session on successful login
if ( !empty( $_POST['password'] ) && $_POST['password'] === $password )
{
// if authenticated, generate a new random session ID
session_regenerate_id();
// set session to authenticated
$_SESSION['auth'] = TRUE;
// redirect to make the new session ID live
header( 'Location: ' . $_SERVER['SCRIPT_NAME'] );
}
// take some action
?>
In my view you can store session id in database when users login and check everyone for the same before loggin in. delete the same session id which you have stored in database when users logout. You can easily findout session id of each and every user or else I can help you.
One of the easy implementations can be done by making a table in database , as logged users , then at login, update that table with user name and his SID , this will prevent other logins as same user , now at the time of log out , just run a simple query , which deletes the logged in data in database , this can also be used to trace logged in user on ur website at a time .
Obviously when you'll set session cookie in the browser, that cookie is sent in the request. Now when request comes, Server will check the session id in database and grant access. To prevent that only its important to store agent and ip so that before checking server makes sure that sessions access is granted to the unique client and not the unique session id which can be hijacked.
I don't know about the coding part well. So I can tell u an algorithm to do this. Setting stuffs like SSL, or setting the session cookie to secure and httpOnly wont work if a user sniffs the session id from a LAN network(Provided user and attacker are in the same LAN).
So what you can do is, once the user successfully logs into the application, set unique token to each and every pages of the web application and keep a track of this at the server side. So that if the valid user sends the request to access a particular page, the token of that page will also be sent to the server side. Since the tokens are unique for a user for a particular session, even if the attacker can get the session id, he cannot hijack the users session as he cannot provide the valid token to the server.
#Anandu M Das:
I believe what you may be referring to is the use of session tokens with each session ID. This site can explain the use of tokens with sessions:
https://blog.whitehatsec.com/tag/session-token/
Although session tokens are easily compromised by an XSS attack, this doesn't mean that they should never be used. I mean let's face it, if something was compromisable by a security vulnerability on the server, its not the fault of the method, its the fault of the programmer who introduced that vulnerability (to highlight points made by Hesson and Rook).
If you follow proper security conventions and practicies and secure your site from SQL injection, XSS, and require all sessions be managed over HTTPS, then you can easily manage the potential attack from CSRF by use of server-side tokens, stored within the session, and updated everytime the user would cause a manipulation to their session (like a $_POST being submitted). Also, NEVER store sessions or their contents in a url, no matter how well you think they are encoded.
When the security of your users is paramount (which it should be), the use of session tokens will allow better or more advanced functionality to be provided without compromising their session security.
I've been researching the best (and safest) ways to implement persistent logins on my website, and I've come up with the following:
When a user logs in, a cookie is created containing the user's ID/username, and a randomly generated number (token). The token is stored in a relational table along with the user ID/username. Every time a members-only page is loaded, this cookie is checked against the relational table, and if it exists and matches with the token, the login is valid and the page can load. If not, however, then the login is invalid, the cookie is destroyed, and the user is prompted to log in.
I was thinking... to save on database access every single time a page is loaded, I could also have a session variable that lasts, say, 10 minutes, and is destroyed automatically when the browser closes. If the session is alive, then it's refreshed and the user can proceed. If the session expires, but the cookie is still valid, check the cookie, reset the token, store that new token in the database (while eliminating the old token, or storing it in an archives table for future reference), and reset the cookie using the new token value.
However, what would the session contain? And how could the session not simply be faked with some JavaScript? Perhaps the session contains a one-way encrypted hash? What would be used to generate that hash (user ID, etc.)?
I'm kind of stuck on where to go from here. I get the cookie stuff, but using temporary sessions (to avoid repeated calls to the database every single time a page is loaded) eludes me. Any help? Thanks.
Cookies should be fine (an alternative would be to store it in the HTTP header), however I don't see the need to store the username/ID in the cookie. The token itself should be enough. You can use a UUID as a token. Store that along with the username and a last_access_timestamp in the database table. And only send the token (in a cookie or in the HTTP request header) on every request. That's enough for implementing sessions in my opinion.
A token is generated on a successful login of a user, stored in the database and passed to the user. Whenever a user accesses the webpage, the token is passen in the request and is validated. If valid the last_acces_timestamp is refreshed and the user can proceed. The lookup in the validation will be done by token and with the username you can do the authentication and authorizaton. If token is invalid or expired, forward the user to a login page.
Deleting expired sessions out of the db can be done periodically using a cron job or on creation of a new session.
For performance reason you might think about storing the session in a hashmap in memory. Since it might be costly to always update the database.
Also think about using HTTPS, to prevent people sniffing the token.
I have solved this the following way, few months ago:
https://stackoverflow.com/questions/12829994/java-custom-session-implementation-expired-sessions
Usage of UUID is not recommended according to RFC 4122 it is stated that
Do not assume that UUIDs are hard to guess; they should not be used as
security capabilities.
I would recommend combining and multiply all of the following information together into a hash with also encrypting it using a public key stored in your server.
UserId (Or User UUID that was generated for each user while registration)
Encrypted His/her password (considered as a private key for encryption per each user)
Time stamp
Client Operating System
Client User Agent (Browser name)
For storing tokens, you could use either memcache which is used heavily in big companies or redis if you are focusing on persistence.
Keep sure that your cookies have the following attributes, for more info about Cookies
HTTP Only cookie
Secure Cookie
How do you prevent multiple clients from using the same session ID? I'm asking this because I want to add an extra layer of security to prevent session hijacking on my website. If a hacker somehow figures out another user's session ID and makes requests with that SID, how can I detect that there are different clients sharing a single SID on the server and then reject the hijack attempt?
EDIT
I have accepted Gumbo's answer after careful consideration because I've come to the realization that what I'm asking for is impossible due to the restrictions of a stateless HTTP protocol. I forgot about what is perhaps the most fundamental principle of HTTP, and now that I think about this question seems a bit trivial.
Let me elaborate what I mean:
After User A logs in on example.com, he is given some random session ID, for simplicity's sake, let it be 'abc123'. This session ID is stored as a cookie on the client side and is validated with a server-side session to ensure the user who logged in remains logged in as he moves from one webpage to another. This cookie of course would not need to exist if HTTP were not stateless. For that reason, if User B steals User A's SID, and creates a cookie on his computer with the value 'abc123', he would have successfully hijacked User A's session, but there is simply no way for the server to legitimately recognize that User B's request is any different from User A's requests, and therefore the server has no reason to reject any request. Even if we were to list the sessions that were already active on the server and try to see if someone is accessing a session that is already active, how can we determine that it is another user who is accessing the session illegitimately and not the same user who is already logged in with a session ID, but simply trying to make another request with it (ie navigate to a different webpage). We can't. Checking the user agent? Can be spoofed - but good as a Defense in Depth measure nevertheless. IP Address? Can change for legitimate reasons - but instead of not checking for the IP address at all, I suggest checking something like the first two octets of the IP, as even a user on a data plan network who constantly has a changing IP for perfectly legitimate reasons would only usually have the last two octets of their IP change.
In consclusion, it is the stateless HTTP that condemns us to never being able to fully protect our websites from session hijacking, but good practices (like the ones Gumbo has provided) will be good enough to prevent a good majority of session attacks. Trying to protect sessions from hijacking by denying multiple requests of the same SID is therefore simply ludicrous, and would defeat the whole purpose of sessions.
Unfortunately, there is no effective way to unmistakably identify a request that originates from an attacker in opposite to a genuine request. Because most properties that counter measures check like the IP address or user agent characteristics are either not reliable (IP address might change among multiple requests) or can be forged easily (e. g. User-Agent request header) and thus can yield unwanted false positives (i. e. genuine user switched IP address) or false negatives (i. e. attacker was able to successfully forge request with same User-Agent).
That’s why the best method to prevent session hijacking is to make sure an attacker cannot find out another user’s session ID. This means you should design your application and its session management that (1) an attacker cannot guess a valid session ID by using enough entropy, and (2) that there is no other way for an attacker to obtain a valid session ID by known attacks/vulerabilities like sniffing the network communication, Cross-Site Scripting, leakage through Referer, etc.
That said, you should:
use enough random input for generating the session ID (see session.entropy_file, session.entropy_length, and session.hash_function)
use HTTPS to protect the session ID during transmission
store the session ID in a cookie and not in the URL to avoid leakage though Referer (see session.use_only_cookies)
set the cookie with the HttpOnly and Secure attributes to forbid access via JavaScript (in case of XSS vulnerabilities) and to forbid transmission via insecure channel (see session.cookie_httponly and session.cookie_secure)
Besides that, you should also regenerate the session ID while invalidating the old one (see session_regenerate_id function) after certain session state changes (e. g. confirmation of authenticity after login or change of authorization/privileges) and you can additionally do this periodically to reduce the time span for a successful session hijacking attack.
Can we do something like this.
Store session id in database.
Also store the Ip address and the HTTP_USER_AGENT for that session id.
Now when a request comes to the server containing that matching session id, Check from which agent and ip it is coming from in your script.
Can make this funda work by make common function or class for session so that every request is verified before it is processed. It would hardly take some micro seconds. But, If many users are visiting your site and you have huge database of sessions, then this might be little performance issue. But, It would surely be very secure compared o other methods like
=> Using regenerating sessions.
In regenerating session ids, there is again little chance of session hijacking.
suppose, user's session id is copied and that user is not working or active for sometime and no request is made to server with old session id asking to regenerate new one. Then In case session id is hijacked, hacker will use that session id and make request to server with that id, then server will respond back with regenerated session id and so that hacker can go on using the services. Actual user will no longer be able to operate because he is unknown of what the regenerated id is and what request session id is to be passed in request. Completely Gone.
Please correct me if i m wrong somewhere.
There are lots of standard defenses against session hijacking. One of them is to match each session to a single IP address.
Other schemes may use an HMAC generated from:
the network address of the client's IP
the user-agent header sent by the client
the SID
a secret key stored on the server
The reason only the network address of the IP is used is in case the user is behind a public proxy, in which case their IP address can change with each request, but the network address remains the same.
Of course, to truly be secure, you really ought to force SSL for all requests so that the SID can't be intercepted by would-be attackers in the first place. But not all sites do this (::cough:: Stack Overflow ::cough::).
Session hijacking is a serious threat, it has to handle by using a secure socket layer for advanced application which involves transactions or by using simple techniques like using cookies, session timeouts and regenerates id etc as explained above.
When the internet was born, HTTP communications were designed to be stateless; that is, a connection between two entities exists only for the brief period of time required for a request to be sent to the server, and the resulting response passed back to the client.
Here are a few methods which hackers follow to hijack the session
Network Eavesdropping
Unwitting Exposure
Forwarding, Proxies, and Phishing
Reverse Proxies
Always recommend SSL Secure Sockets Layer
Use cookies also to following ini_set() directives at the start of your scripts, in order to override any global settings in php.ini:
ini_set( 'session.use_only_cookies', TRUE );
ini_set( 'session.use_trans_sid', FALSE );
Use Session Timeouts and Session Regenerate ID
<?php
// regenerate session on successful login
if ( !empty( $_POST['password'] ) && $_POST['password'] === $password )
{
// if authenticated, generate a new random session ID
session_regenerate_id();
// set session to authenticated
$_SESSION['auth'] = TRUE;
// redirect to make the new session ID live
header( 'Location: ' . $_SERVER['SCRIPT_NAME'] );
}
// take some action
?>
In my view you can store session id in database when users login and check everyone for the same before loggin in. delete the same session id which you have stored in database when users logout. You can easily findout session id of each and every user or else I can help you.
One of the easy implementations can be done by making a table in database , as logged users , then at login, update that table with user name and his SID , this will prevent other logins as same user , now at the time of log out , just run a simple query , which deletes the logged in data in database , this can also be used to trace logged in user on ur website at a time .
Obviously when you'll set session cookie in the browser, that cookie is sent in the request. Now when request comes, Server will check the session id in database and grant access. To prevent that only its important to store agent and ip so that before checking server makes sure that sessions access is granted to the unique client and not the unique session id which can be hijacked.
I don't know about the coding part well. So I can tell u an algorithm to do this. Setting stuffs like SSL, or setting the session cookie to secure and httpOnly wont work if a user sniffs the session id from a LAN network(Provided user and attacker are in the same LAN).
So what you can do is, once the user successfully logs into the application, set unique token to each and every pages of the web application and keep a track of this at the server side. So that if the valid user sends the request to access a particular page, the token of that page will also be sent to the server side. Since the tokens are unique for a user for a particular session, even if the attacker can get the session id, he cannot hijack the users session as he cannot provide the valid token to the server.
#Anandu M Das:
I believe what you may be referring to is the use of session tokens with each session ID. This site can explain the use of tokens with sessions:
https://blog.whitehatsec.com/tag/session-token/
Although session tokens are easily compromised by an XSS attack, this doesn't mean that they should never be used. I mean let's face it, if something was compromisable by a security vulnerability on the server, its not the fault of the method, its the fault of the programmer who introduced that vulnerability (to highlight points made by Hesson and Rook).
If you follow proper security conventions and practicies and secure your site from SQL injection, XSS, and require all sessions be managed over HTTPS, then you can easily manage the potential attack from CSRF by use of server-side tokens, stored within the session, and updated everytime the user would cause a manipulation to their session (like a $_POST being submitted). Also, NEVER store sessions or their contents in a url, no matter how well you think they are encoded.
When the security of your users is paramount (which it should be), the use of session tokens will allow better or more advanced functionality to be provided without compromising their session security.
I am making a login script that I would like to be as secure as possible. Problem is, security seems to be a never ending battle. So essentially, I am looking for suggestions and improvements to my ideas.
What I have is a login based solely on sessions. Anytime the session information changes, session_regenerate_id() is called to avoid obvious hijacking attempts.
When the session is not set, I check a cookie for valid login, and on success, I update the session.
I attempt to secure the cookie by adding a hash value along with a piece of unique user information (like username or id). This hash is comprised of various information, including the username/id, undecipherable password hash, part of the IP address, etc. By extracting the username/id from the cookie, I can make a new hash from the valid user information and compare that with the hash in the cookie. My hopes here are to prevent fake cookies and cookie hijacking (unless they also spoof the IP address).
EDIT Assume that the login itself will be done via HTTPS/SSL, so the transfer is (reasonably) secure.
Am I on the right track? What else can be done to secure my login?
Thanks for the help!
Stop what you are doing. Do not check the user-agent or the ip address. The user-agent is an attacker controlled variable and checking this value does not increase the security of this system. The ip address will change for legitimate reasons, such as if a user is behind a load balancer or TOR.
A session id must always be a cryptographic nonce. In php just call session_start() and then start using the $_SESSION super global. PHP takes care of all of this for you. If you want to improve php's session handler, use the configurations. Enable use_only_cookies, cookie_httponly and cookie_secure. Also setting the entropy_file to /dev/urandom is a good idea if you are on a *nix system but if your under windows then your in trouble.
For instance to authenticate a user:
//In a header file
session_start();
...
if(check_login($_POST['user_name'],$_POST['password'])){
//Primary key of this user
$_SESSION['user_id']=get_user_id($_POST['user_name']);
$_SESSION['logged_id']=True;
}
And to verify if a user is logged in:
//in a header file
session_start()
...
if(!$_SESSION['logged_id']){
header("location: login.php");
die();//The script will keep executing unless you die()
}
To improve this system read OWASP A9 and use HTTPS for the entire life of the session. Also read OWASP A5: CSRF aka "session riding" and OWASP A2: XSS because they can both be used to compromise a session.
There is no such thing as secure cookie UNLESS it's transmitted over SSL only. It can be mitigated some when using a persistent non-session cookie (like remember me), by doing exactly what you're doing, but not in the same way you're thinking of doing it.
You can indeed store server variables such as the user-agent, the ip address and so forth (and even JavaScript variables), but they are only good for validating that the persistent cookie data matches the client's new connection. The ip address isn't a good idea except when you know that the client (like you only) isn't going to change on every page load (a la AOL).
Modern web browsers and 3rd party services like LastPass can store login credentials that only require a key press (and sometimes not even that) to send the data to the login form. Persistent cookies are only good for those people who refuse to use what's available otherwise. In the end, persistent, non-session cookies are not really required anymore.
I use a cookie based method (using setcookie function) but ....
session_start();
...
if(check_login($_POST['user_name'],$_POST['password'])){
//Primary key of this user
$_SESSION['user_id']=get_user_id($_POST['user_name']);
$_SESSION['logged_id']=True;
}
...these methods are wrooooong !!!!
I crack my website with an attack based on the cookie.
I used cookie option of the WebCruiser vulnerability scanner, so I get my cookie after login.
Then I changed a simply value on cookie
Then I clicked save cookie.
At this point I clicked on webbrowser see on the left panel then I clicked right then I clicked on refresh page, so I got my admin page without using the login page with user and password.
So if someone push you a virus to read the cookie history of IE or Firefox, you'll be happy to find out your admin user and pass can be used by others.
So how to fix the problem? Simple: combine the cookie with session server or session's cookie with sessions server, or session with file session, or cookie with file session....
will be secure but slow :((((
I keep all login data in the users session, this way its all stored server side.
The only thing i would store in a client cookie is stuff like 'auto login', 'session id'
SESSION more secure than cookie
and my advise is to create a unique id for the current login attempted
like :
$id = uniqid();
$_SESSION['username'.$id] = "something ...";
So on my application login form I've got one of those little boxes like [_]remember me
When the user checks that we set $_COOKIE['rememberMe'] with the value of the username. Now when that user comes back 3 days later, I obviously want to recognize them and re-log them in automatically. It doesn't sound safe to simply check for the existence of that cookie and then use it's value as the username to login without a password. But I'm not sure how else I would log them automatically... Is there a way this usually done?
Your cookie should have three values:
1. username
2. expiration time
3. a session code
When a user logs in, generate a session code and set an expiration time.
Store that session code and expiration time in the cookie and on your database.
Then whenever user returns to the site, and if user is not logged in:
1. check for the cookie
2. check for the cookie against the database
If all three variable matches and the expiration time is not over, log the user in.
Alternatively, if you simply encode the session code as say a md5 of ($username.$expiration_time), then you won't have to set up a database for storing and checking. Although having a database with randomly generated session code is much safer.
This is extremely unsafe. Since the cookie is the only thing you have to go by and the cookie is transferable from system to system, you would be vulnerable to cookie poisoning attacks and cookie copying attacks. If this is indeed the course you're set on, you will need to use some manner of foot-printing the user's system and storing that information in a database somewhere possibly as part of a persistent session on a session state server. This information could then be compared with the new login so if the cookie is transferred to a different system, it will not match and the automatic login will fail. As for accomplishing the login, I would recommend at a minimum to have a session state database where session information could be stored per session ID and username. If these 2 items are stored in the cookie, this information could then be used to get the information out of the database, and the foot-printing could be used as a stop-gap (although a very weak one) to prevent misuse.
The only information you need to store in a cookie is some unique hash that's going to point to the right user session in your system. Storing username or other information is redundant and unsafe considering the fact that username can be captured by an attacker and used with a combination of other information. To make the system more safe, you should implement a layer that'd check user's location by the IP address and his browser details. I suggest you should learn from what companies like Facebook and Google do with user accounts.
Place a random and uniqe hash in the cookie and store it in DB too with the current client's IP address.
If the user comes back, you can search for the hash in your DB.