This document summarizes security issues with single sign-on systems like OpenID and provides recommendations. It describes 7 attacks that can occur: (1) observing username/password combinations, (2) choosing misleading URLs, (3) exploiting weaknesses in crypto protocols, (4) phishing through malicious sites, (5) privacy issues from sharing login data, (6) replay attacks despite nonces, and (7) cross-site request forgery. While having a single sign-on is useful, the document argues flexibility must be reduced and security strengthened to prevent these attacks, such as using client certificates. Overall, OpenID can work but needs more focus on privacy and security issues.

1. Single Sign-On for the Internet: A Security Story [email_address] [email_address] BlackHat USA, Las Vegas 2007

2. The Good, The Bad, The Ugly

3. The Ugly

4. How do you manage your 169 Web 2.0 accounts today?

5. Does your “SSO” consist of A login (e.g. johndoe) + 2 passwords (one insecure for web 2.0 sites and one secure for banking sites) ?

6. Attack #1 a. Fail a user’s login b. Observe the user try every single combination of their username and password, including the secure password..

7. BlackHat Advice #1 Change your bank password (we man-in-the-middle’d your secure “SSO” last night)

8. Observation #1 Complexity breeds insecurity

9. One login to rule them all… … a story about reducing complexity

10. Proves that a user owns a URL You get to choose who manages your identity e.g. http://john.doe.name/ or http://john.myopenid.com/

11. Answers the who? question (authentication) are you john.doe.name? Does NOT answer the what? (authorization) is john.doe.name allowed to access this page?

12. History Specifications Industry Support

13. How? (demo)

14. How? (man-in-the-middle secure demo)

19. That was easy!

20. Oh. Never mind.

21. The Bad

22. Let’s start at the beginning

24. Attack #2 – Which one are you? http://nsa.gov:1/, http://nsa.gov:2/, … https://192.168.1.15/internal/auth?ip=1.1.1.1 http://localhost:8080/ http://www.youtube.com/largemovie.flv http://www.tarpit.com/cgi-bin/hang.pl file:///dev/null

25. Observation #2 Flexibility and security do not get along (or, why it’s important to be less flexible and more paranoid)

26. Everybody loves crypto “ associate mode”

27. Why is crypto required? to protect request & response URLs

28. Shared symmetric key is generated using Diffie-Hellman

29. Attack #3 - Diffie-Hellman is vulnerable to man-in-the-middle attacks! So what’s the point of using DH in the first place? The spec suggests running DH over https to improve protocol security

30. Observation #3 Home brewed crypto is a no no (or, why you should stick to https)

31. Where are you going?

32. This way! No, that way! Location: http://www.myopenid.com/server? openid.assoc_handle =%7BHMAC-SHA1%7D%7B4..& openid.identity =http://eugene.tsyrklevich.name/& openid.mode =checkid_setup& openid.return_to =http://www.jyte.com/finish& openid.trust_root =http://www.jyte.com/

33. Attack #4a Phishing with malicious RPs

34. Attack #4b Phishing with malicious URL hosts

35. Change your bank password BlackHat Advice #2 (we phish’ed your first attempt)

36. Observation # 4 Phishers 1 – OpenID 0 (or, why Johnny will never learn to read URLs)

37. Let me in!

38. Once signed in, you will no longer need to re-enter your password for other OpenID enabled sites Convenient, eh?

39. In other words… your identity provider receives and processes ALL your login requests on your behalf … privacy, anyone?

40. Observation #5 OpenID makes privacy difficult (or, why some paranoid users might want to use one OpenID login per site)

41. Not another redirect!

42. Location: http://www.BADsite.com/finish_auth.php? openid.assoc_handle =%7BHMAC-HA1%7D%7B47bb..& openid.identity =http://eugene.tsyrklevich.name/& openid.mode =id_res& openid.return_to =http://www.jyte.com/& openid.sig =vbUyND6n39Ss8IkpKl19RT83O%2F4%3D& openid.signed =mode%2Cidentity%2Creturn_to& Attack #6a – Phishing (again!)

43. Location: http://www.somesite.com/finish_auth.php? openid.assoc_handle =%7BHMAC-SHA1%7D%7B47b..& openid.identity =http://eugene.tsyrklevich.name/& openid.mode =id_res& openid.return_to =http://www.jyte.com/& openid.sig =vbUyND6n39Ss8IkpKl19RT83O%2F4%3D& openid.signed =mode%2Cidentity%2Creturn_to& Attack #6b – Replay attack nonce=wVso75KH

44. Problems with Nonces a. Not part of the OpenID spec (v1) b. Do not actually protect against active attackers!

45. Observation #6 Nonces are nonsense (or, why you must be drinking absolut kool-aid if you believe nonces will protect you against an active attacker)

46. I am secure once I am logged in though, right?

47. Attack #7 Cross-site request forgery <html><body> <iframe id=&quot; login &quot; src=&quot; http://bank.com/login?openid_url=john.doe.name &quot; width=&quot; 0 &quot; height=&quot; 0 &quot; ></iframe> <iframe id=“ transfer &quot; src=&quot; http://bank.com/transfer_money?amount=100&to=attacker &quot; width=&quot; 0 &quot; height=&quot; 0 &quot; ></iframe> </body></html>

48. Observation #7 OpenID robs you of control (or IdP, not RP, makes the security decisions)

49. Change your bank password BlackHat Advice #3 Actually don’t bother… ...all your OpenID are belong to us.

50. The Good

51. Is it really all that bad?! No! OpenID can make your logins far more secure than they are today!

52. How?! Only one service to secure so we can afford to use Client-side certificates SecurID Smartcards

54. Observation #8 There is only 1 front door with OpenID (or, how I got over my privacy and learnt to love OpenID)

55. Lessons Learnt Complexity breeds insecurity Flexibility and security do not get along Home brewed crypto is a no no Phishers 1 – OpenID 0 OpenID makes privacy difficult Nonces are nonsense OpenID robs you of control There is only 1 front door with OpenID

56. Is OpenID doomed? Absolutely not It’s a great system solving a very real problem But its security and privacy concerns need further thought

57. Thanks! [email_address] [email_address] Try it today. http://www.openid.net/ http://www.freeyourid.com/