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On Stack Exchange's Add a login page, one can add logins with Google, Facebook, Yahoo, etc. How many logins should I have to provide the least chance of a hacker gaining access to my Stack Exchange account, and the best recovery in case they do?

One? As many as possible? My undoubtedly incorrect assumption is that I should have two, so that:

  • There are less sites that can be hacked into to gain access to my Stack Exchange account;
  • If one of the two does get hacked, and, for example, its password is changed, I'll still be able to regain control of my Stack Exchange account with the other site's account that did not get hacked.
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"the least chance of a hacker gaining access to my Stack Exchange account, and the best recovery in case they do?" Pretty sure you can't have both at once, and there may be more than one distinct point on the Pareto front of the trade-off. Possibly all answers are Pareto optimal: that just requires that risk and recovery both increase with additional logins. –  Steve Jessop Apr 17 at 17:36

5 Answers 5

up vote 10 down vote accepted

If someone compromises your StackExchange account can't they just unlink all your recovery options? Assuming they can't, the model is that:

  • Losing any of the accounts linked to SE is a "compromise".
  • If any of the other accounts linked to SE is not lost then you can "recover".

On this model, 2 seems reasonable by your own analysis:

  • 0 is no good, you can't log in to SE at all ;-)
  • 1 is no good, you have no chance of recovery following a compromise.
  • 2 is the least number of accounts with non-zero chance of recovery. Provided that losing one does not compromise the other, then in fact it gives you a pretty good chance of recovery, since losing accounts is rare and losing two in quick succession is very rare.
  • Additional accounts increase the chance of compromise, and the additional chance of recovery must diminish rapidly because the recovery chance is already good.

As I said, however, I'm not confident of the model. I've never tried to unlink something from my SE account.

The provided is quite a big one. If your Gmail account is also the recovery option for your Facebook, then losing your Gmail account means you've a fair chance of losing Facebook too. So adding Facebook to StackExchange would have a less dramatic effect on your chance of recovery following compromise via Gmail.

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Adding logins means adding alternative methods to access your account; see this page for details.

Thus, additional logins cannot reduce the risk of hostile hijack; in fact, they can only increase the risk since they provide additional entry routes for the attacker. If you have several logins, then your "security level", formally, is no more than that provided by the weakest of the involved authentication systems.

Additional logins are meant to avoid being locked out if an authentication provider fails (e.g. ceases to operate). This can be viewed as extra "security", not against attackers, but against disasters.

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+1, but that's pretty much what I said in my question. The actual question is "how many should I have" –  The Guy with The Hat Apr 17 at 13:09
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The logic is simple: if you want to minimize the risks of hostile hijack, have only one login. If you want to minimize the risks of being locked out, have at many as possible. This is a trade-off, and only you can make that decision. (However, one possible "login" option is through stackexchange themselves, which is unlikely to close independently of the site itself, so maybe "just one, the one provided by stackexchange" would be the optimal spot.) –  Tom Leek Apr 17 at 13:18

Simply put, additional logins would have 2 effects:

  • It increases the risk of attacks and account compromission

but on the other hand,

  • It lowers the impact of a successful attack by limiting the perimeter of data accessed.

Then it's up to you to decide based on the risk you accept, and the balance you want in terms of usability versus security.

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Before addressing the "hacker gaining access to my Stack Exchange account" using 3rd party authentication, shouldn't you be addressing the security of your 3rd party OpenID/OAuth provider? Sign up for two-factor authentication.

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My recommendation is either:

1, based on Stack Exchange's own login system. There's absolutely no good reason to crosslink systems.

or

1, based on some trusted shared identity hub, if you're already using such a hub other than Stack Exchange's own system. Assuming you have found a single-sign-on system that you do trust. I haven't yet seen one on the public net that I consider worth using.

The serious concern isn't so much losing access to your Stack Exchange identity (if that happens you start again with a new username, and need to work with SE a bit to shut down the old ID and clean up any abusive posts that were made in your name if someone else got access to it; that's a nuisance at worst) as that someone breaking into SE might be able to gain access to your accounts elsewhere.

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