1. Online Security Tuesday April 8, 2003 Maxence Crossley

2. Outline  How do we authenticate a service?  How do we encrypt a session?  How do we prevent a “replay attack”?  Another Problem: Spoofing

3. How do we authenticate a session?  Certification Authorities (CAs)  VeriSign  SecureNet  Digital Signature Trust  Distribute and store certificates

4. Public Key Cryptography  Server publishes public key with Certification Agency  Client encrypts message with public key  Server decrypts message with private key Source: http://waubonsie.com/security/www.htmlhttp://waubonsie.com/security/www.html

5. Private Key Cryptography  Server and Client share a secret and private key  Client encrypts message with private key  Server decrypts message with private key Source: http://waubonsie.com/security/www.htmlhttp://waubonsie.com/security/www.html

6. How do we encrypt a session? SSL  Client requests a secured file  Server sends its certificate  Client checks with CA that the signature is valid  Client generates a unique session key and sends it to server Source: http://waubonsie.com/security/www.htmlhttp://waubonsie.com/security/www.html

7. How do we encrypt a session? Source: http://waubonsie.com/security/www.htmlhttp://waubonsie.com/security/www.html

8. How do we encrypt a session? Source: http://waubonsie.com/security/www.htmlhttp://waubonsie.com/security/www.html

9. How do we encrypt a session? Source: http://waubonsie.com/security/www.htmlhttp://waubonsie.com/security/www.html

10. What is a “replay attack”?  When an attacker uses captured authentication tokens to gain access to a user’s account while bypassing normal authentication  Sniffing a URL that has a session ID in it  Attacker can obtain access to users account Source: http://www.owasp.org/asac/auth-session/replay.shtmlhttp://www.owasp.org/asac/auth-session/replay.shtml

11. Countermeasures Source: http://www.owasp.org/asac/auth-session/replay.shtmlhttp://www.owasp.org/asac/auth-session/replay.shtml  “Generate hard to reverse-engineer Session IDs for authenticated web users (i.e. use strong crypto, MD5 hashes, etc.)”  “Build and require SSL (or other encryption) into the web application so that the authentication token can not be easily sniffed in transit between browser and server; Ensure that all cookies enable the "secure" field (see OWASP's explanation of cookies)”

12. Countermeasure Source: http://www.owasp.org/asac/auth-session/replay.shtmlhttp://www.owasp.org/asac/auth-session/replay.shtml  “Provide a logout function that expires all cookies and other authentication tokens”  “Users can choose not to select the "Remember Me" option on web application accounts so that authentication tokens are not persistent after logout”

13. Another Problem: Spoofing  Web users rely on visual clues when deciding to trust a site  Location bar information  SSL icons  SSL warnings  Certificate information  Response time  These cues can be forged Source: http://www.cs.dartmouth.edu/~pkilab/demos/spoofing/http://www.cs.dartmouth.edu/~pkilab/demos/spoofing/

14. Spoofing Source: http://www.cs.dartmouth.edu/~pkilab/demos/spoofing/http://www.cs.dartmouth.edu/~pkilab/demos/spoofing/

15. Spoofing Source: http://www.cs.dartmouth.edu/~pkilab/demos/spoofing/http://www.cs.dartmouth.edu/~pkilab/demos/spoofing/

16. Countermeasures  Mozilla with SRD (synchronized random dynamic) Boundary  Trusted Reference Window in lower right corner  Untrusted Outer Window  Colors chosen at random Source: http://www.cs.dartmouth.edu/~pkilab/demos/countermeasures/http://www.cs.dartmouth.edu/~pkilab/demos/countermeasures/