• It’s this time of year again, sending emails from Thunderbird fails with an error message:

    The certificates I use to sign my emails have expired. So I once again need to go through the process of getting replacements. Or I could just give up on email signing and encryption. Right now, I am leaning towards the latter.

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  • TL;DR: The answer to the question in the title is most likely “no.” While the OPAQUE protocol is a fascinating approach to authentication, for web applications it doesn’t provide any security advantages.

    I read an interesting post by Matthew Green where he presents ways to authenticate users by password without actually transmitting the password to the server, in particular a protocol called OPAQUE. It works roughly like that:

    The server has the user’s salt and public key, the client knows the password. Through application of some highly advanced magic, a private key materializes in the client, matching the public key known to the server. This only works if the password known to the client is correct, yet the client doesn’t learn the salt and the server doesn’t learn the password in the process. From that point on, the client can sign any requests sent to the server, and the server can verify them as belonging to this user.

    The fact that you can do it like this is amazing. Yet the blog post seems to suggest that websites should adopt this approach. I wrote a comment mentioning this being pointless. The resulting discussion with another commenter made obvious that the fundamental issues of browser-based cryptography that I first saw mentioned in Javascript Cryptography Considered Harmful (2011) still aren’t widely known.

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  • A few days ago Google announced ensuring privacy for your Android data backups. The essence is that your lockscreen PIN/pattern/passcode is used to encrypt your data and nobody should be able to decrypt it without knowing that passcode. Hey, that’s including Google themselves! Sounds good? Past experience indicates that such claims should not always be taken at face value. And in fact, this story raises some red flags for me.

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  • Two days ago I decided to take a look at Keybase. Keybase does crypto, is open source and offers security bug bounties for relevant findings — just the perfect investigation subject for me. It didn’t take long for me to realize that their browser extension is deeply flawed, so I reported the issue to them via their bug bounty program. The response was rather… remarkable. It can be summed up as: “Yes, we know. But why should we care?” Turns out, this is a common response, see update at the bottom.

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  • Dear developers of password managers, we communicate quite regularly, typically within the context of security bug bounty programs. Don’t get me wrong, I don’t mind being paid for finding vulnerabilities in your products. But shouldn’t you do your homework before setting up a bug bounty program? Why is it the same basic mistakes that I find in almost all password managers? Why is it that so few password managers get AutoFill functionality right?

    Of course you want AutoFill to be part of your product, because from the user’s point of view it’s the single most important feature of a password manager. Take it away and users will consider your product unusable. But from the security point of view, filling in passwords on the wrong website is almost the worst thing that could happen. So why isn’t this part getting more scrutiny? There is a lot you can do, here are seven recommendations for you.

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