Yahoo! Yippee? What to Do?

by adam on December 15, 2016

[Dec 20 update: The first draft of this post ended up with both consumer and enterprise advice, which made it complex. The enterprise half is now on the IANS blog: Never Waste a Good Crisis: Yahoo Edition.]

Yesterday, Yahoo disclosed that attackers broke into Yahoo in 2013 and stole details on a billion accounts. Brian Krebs summarizes what was taken, and also has a more general FAQ.

The statement says that for “potentially affected accounts, the stolen user account information may have included names, email addresses, telephone numbers, dates of birth, hashed passwords (using MD5) and, in some cases, encrypted or unencrypted security questions and answers.”

Yahoo says users should change their passwords and security questions and answers for any other accounts on which they used the same or similar information used for their Yahoo account.

The New York Times has an article “How Many Times Has Your Personal Information Been Exposed to Hackers?

The big question is “How can you protect yourself in the future?” The Times is right to ask it, and their answer starts:

It’s pretty simple: You can’t. But you can take a few steps to make things harder for criminals. Turn on two-factor authentication, whenever possible. Most banking sites and ones like Google, Apple, Twitter and Facebook offer two-factor authentication. Change your passwords frequently and do not use the same password across websites.

I think the Times makes two important “mistakes” in this answer. [Update: I think mistake may be harsher than I mean: I wish they’d done differently.]

The first mistake is to not recommend a password manager. Using a password manager is essential to using a different password on each website. I use 1Password, and recommend it. I also use it to generate random answers to “security questions” and use 1Password’s label/data fields to store those. I do hope that one day they start managing secret questions, but understand that that’s tricky because secret questions are not submitted to the web with standard HTML form names.

The reason I recommend 1Password is that it works well without the cloud, and that means that a cloud provider cannot disclose my passwords. They also can’t disclose my encrypted passwords, where encrypting them is a mitigation for that first-layer information disclosure threat. (One of these days I should write up my complete password manager threat model.) These threats are important and concrete. 1Password competitor Lastpass has repeatedly messed this up, and those problems are made worse by their design of mandatory centralization.

It’s not to say that 1Password is perfect. Tavis Ormandy has said “More password manager bugs out today and more due out soon. I’m not going to look at more, the whole industry is crazy,” and commented on 1Password with a GIF. Some of those issues have now been revealed. (Tavis is very, very good at finding security flaws, and this worries me a bit.)

But: authentication is hard. You must make a risk tradeoff. The way I think about the risk tradeoff is:

  • If I use a single password, it’s easily compromised in many places. (Information disclosure threats at each site, and in my browser.)
  • If I use a paper list, an attacker who compromises my browser can likely steal most of my passwords.
  • If I use a cloud list, an attacker who breaks into that cloud can steal the list. If the list is encrypted, then they can still attack it offline. If the cloud design either sends my master password to the cloud, or javascript to the client, then my master password is vulnerable to an attacker who has broken into the cloud.
  • If I use a paper list, I can’t back it up easily. (My backups are on my phone, and in a PGP encrypted file on a cloud provider.)

So 1Password is the least bad of currently available options, and the Times should have put a stake in the ground on the subject. (Or perhaps their new “Wirecutter” division should take a look. Oh wait! They did. I disagree with their assessment, as stated above.)

The second big mistake is to assert that you can’t fully protect yourself in a simple, declarative sentence at the end of their answer. What’s that you say? It’s not the end of their answer? But it is. In today’s short attention-span world, you see those words and stop. You move on. It’s important that security advice be actionable.

So: use a password manager. Lie in your answers to “secret questions.” Tell different sites different lies. Use a password manager to remember them.

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