Cookie expiration and security in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the 'expires' attribute in a cookie do?

The 'expires' attribute sets the date and time when the cookie will be deleted by the browser. After this time, the cookie is no longer sent with requests.

beginner

What is the purpose of the 'Secure' flag in a cookie?

The 'Secure' flag ensures the cookie is only sent over HTTPS connections, protecting it from being sent over unencrypted HTTP.

intermediate

How does the 'HttpOnly' flag improve cookie security?

The 'HttpOnly' flag prevents JavaScript from accessing the cookie, reducing the risk of cross-site scripting (XSS) attacks stealing the cookie.

intermediate

What is the difference between 'expires' and 'max-age' attributes in cookies?

'expires' sets a fixed date/time for cookie expiration, while 'max-age' sets the lifetime in seconds from the current time. 'max-age' is newer and preferred for relative expiration.

intermediate

Why should you set the 'SameSite' attribute on cookies?

The 'SameSite' attribute restricts how cookies are sent with cross-site requests, helping to prevent cross-site request forgery (CSRF) attacks.

Which cookie attribute ensures the cookie is only sent over HTTPS?

A Secure

B HttpOnly

C SameSite

D Expires

The 'Secure' attribute makes sure the cookie is sent only over HTTPS connections.

What does the 'HttpOnly' flag prevent?

A Cross-site request forgery

B Cookie expiration

C Sending cookie over HTTP

D Access to the cookie via JavaScript

'HttpOnly' prevents JavaScript from accessing the cookie, protecting it from XSS attacks.

If you want a cookie to expire in 1 hour from now, which attribute is best to use?

A expires with a fixed date 1 hour later

B max-age set to 3600 seconds

C HttpOnly

D Secure

'max-age' sets the cookie lifetime in seconds from now, so 3600 means 1 hour.

What is the main security benefit of setting 'SameSite' to 'Strict'?

A Allows cookies to be accessed by JavaScript

B Makes cookies expire immediately

C Prevents cookies from being sent with cross-site requests

D Encrypts the cookie data

'SameSite=Strict' blocks cookies from being sent on cross-site requests, reducing CSRF risks.

Which PHP function is used to set a cookie with expiration and security flags?

A setcookie()

B cookie_set()

C set_cookies()

D cookie()

The PHP function 'setcookie()' is used to create cookies with options like expiration, Secure, and HttpOnly.

Explain how to set a cookie in PHP that expires in 2 hours and is secure and HttpOnly.

Think about the parameters of setcookie() including options array.

Describe why cookie security flags like Secure, HttpOnly, and SameSite are important.

Consider common web security threats related to cookies.

Practice

1. What does setting the expires parameter in setcookie() control?

easy

A. How long the cookie stays on the user's browser

B. The name of the cookie

C. The value stored inside the cookie

D. The domain where the cookie is valid

Solution

1. Step 1: Understand the purpose of the expires parameter

   The expires parameter sets the time when the cookie will be deleted by the browser.

2. Step 2: Relate expires to cookie lifetime

   Setting expires controls how long the cookie remains stored on the user's device.

3. Final Answer:

   How long the cookie stays on the user's browser -> Option A

4. Quick Check:

   Cookie expiration = lifetime on browser [OK]

Hint: Expires means cookie lifetime in browser [OK]

Common Mistakes:

• Confusing expires with cookie name or value
• Thinking expires controls cookie content
• Mixing expires with domain or path

2. Which of the following is the correct way to set a cookie with secure and HttpOnly flags in PHP?

easy

A. setcookie('user', 'John', time() + 3600, '/', '', true, false);

B. setcookie('user', 'John', time() + 3600, '/', '', false, true);

C. setcookie('user', 'John', time() + 3600, '/', '', true, true);

D. setcookie('user', 'John', time() + 3600, '/', true, true);

Solution

1. Step 1: Recall setcookie() parameters order

   The parameters are: name, value, expire, path, domain, secure, httponly.

2. Step 2: Identify correct secure and httponly flags

   Setting secure to true means cookie sent only over HTTPS, and httponly true means inaccessible to JavaScript.

3. Final Answer:

   setcookie('user', 'John', time() + 3600, '/', '', true, true); -> Option C

4. Quick Check:

   Secure and HttpOnly flags = true, true [OK]

Hint: Secure is 6th, HttpOnly is 7th parameter in setcookie [OK]

Common Mistakes:

• Mixing order of parameters
• Setting secure or httponly to false by mistake
• Omitting parameters causing errors

3. What will be the output of this PHP code?

setcookie('test', '123', time() - 3600);
if(isset($_COOKIE['test'])) { echo 'Cookie set'; } else { echo 'Cookie not set'; }

medium

A. Cookie set

B. Cookie not set

C. Syntax error

D. Empty output

Solution

1. Step 1: Understand the expiration time used

   The cookie is set with an expiration time in the past (time() - 3600), which deletes the cookie immediately.

2. Step 2: Check if cookie exists after deletion

   Since the cookie is expired, $_COOKIE['test'] will not be set, so the else branch runs.

3. Final Answer:

   Cookie not set -> Option B

4. Quick Check:

   Expired cookie = not set [OK]

Hint: Past expiration deletes cookie, so isset returns false [OK]

Common Mistakes:

• Assuming cookie is set immediately after setcookie
• Ignoring expiration time meaning
• Confusing server and client cookie states

4. Identify the error in this PHP code snippet for setting a secure cookie:

setcookie('session', 'abc123', time() + 3600, '/', '', 'true', true);

medium

A. The secure flag is a string instead of boolean

B. The expiration time is in the past

C. The cookie name is invalid

D. Missing path parameter

Solution

1. Step 1: Check parameter types in setcookie()

   The secure parameter must be a boolean (true/false), not a string.

2. Step 2: Identify the incorrect usage

   Here, 'true' is a string, which PHP treats as true but is incorrect usage and can cause unexpected behavior.

3. Final Answer:

   The secure flag is a string instead of boolean -> Option A

4. Quick Check:

   Secure flag must be boolean, not string [OK]

Hint: Use true/false without quotes for flags [OK]

Common Mistakes:

• Using 'true' or 'false' as strings
• Forgetting to set secure flag for HTTPS
• Omitting required parameters

5. You want to set a cookie named auth that lasts exactly 2 hours, is only sent over HTTPS, and cannot be accessed by JavaScript. Which of the following is the best way to do this?

hard

A. setcookie('auth', 'token', time() + 3600, '/', '', true, false);

B. setcookie('auth', 'token', time() + 7200, '/', '', false, true);

C. setcookie('auth', 'token', time() + 7200, '/', '', true, false);

D. setcookie('auth', 'token', time() + 7200, '/', '', true, true);

Solution

1. Step 1: Calculate correct expiration time

   2 hours = 7200 seconds, so expiration should be time() + 7200.

2. Step 2: Set secure and httponly flags correctly

   Secure flag true ensures HTTPS only; httponly true prevents JavaScript access.

3. Step 3: Verify all parameters

   Path is '/', domain is default '', flags are true, true matching requirements.

4. Final Answer:

   setcookie('auth', 'token', time() + 7200, '/', '', true, true); -> Option D

5. Quick Check:

   2 hours + secure + httponly = setcookie('auth', 'token', time() + 7200, '/', '', true, true); [OK]

Hint: Use time()+7200, secure=true, httponly=true for 2hr secure cookie [OK]

Common Mistakes:

• Using wrong expiration time
• Not setting secure flag for HTTPS
• Leaving httponly false allowing JS access