4 is the new funny number. All other funny numbers are thereby declared obsolete.

@vaporeon_ I missed the context for this, why were you and someone else posting about 4?

but also, 4 is death https://en.wikipedia.org/wiki/Tetraphobia

@The_T Do you know about TLS certificates? They are used to encrypt a HTTPS connection, and also to prove that a web site really is the server it claims to be and not someone intercepting your connection and directing it somewhere else. But for that to work, ultimately you need to trust a Certificate Authority's certificates.

And some CA that I've never heard of before messed up and used 4 as the private key for one of those certificates (and very small numbers for the others).

And so now I, or anyone else, can create new certificates without anyone's approval and sign them as the CA who messed up, and pretend to be any web site

@The_T A private key should be a very big number that's basically impossible to guess

So it's inherently funny for it to be... 4

@The_T If you're now worried about whether you're affected, this is a web site (not mine) where you can test it: https://emudhra.we-have-a-problem.com/

@vaporeon_ I was aware of TLS certificates, but I've never understood how they worked. And your explanation about, requiring to trust a CA, makes sense, but then a mistake like this also seems... well, not inevitable, but unsurprising?

But yeah that is pretty funny

"if I'm affected" would only be if I had a website, right? or is it for websites I use? I think they'd have bigger problems, though...

@The_T Not only if you had a web site, if you connect to any web site, it's a bad problem

Imagine you connect to https://glaceon.social
glaceon.social sends to your browser a chain of certificates (if you're curious, in Firefox, you can click on the lock icon -> "Encrypted connection" -> "Details" -> "View certificate"), each certificate signed by the private key of the previous certificate. If e.g. glaceon.social's certificate is signed by Let's Encrypt, that means Let's Encrypt vouches for glaceon.social to really be who it claims to be, and then someone else signs Let's Encrypt's certificate, and so on, up to a root certificate that's stored in your browser and trusted unconditionally. The browser verifies this chain before establishing the connection to glaceon.social and sending them e.g. your password.

Now imagine Let's Encrypt's private key got leaked (it did not, another CA called "eMudhra" did, but that's just as bad because there's no limitation on which web site a CA can issue certificates for)

Then anyone could create a fake glaceon.social certificate, sign it with Let's Encrypt's private key, serve it on an evil web site pretending to be glaceon.social, and browsers would accept the fake certificate without complaining

The attacker would also need to intercept your connection first, which somewhat limits who can do this attack, but still, it is worth fixing ASAP if you're affected

@vaporeon_ mm, that makes sense.

Sounds like nothing I can do, though. 🤷

@The_T Do you use Firefox? In Firefox, you can manually revoke the compromised certificates so that your browser doesn't trust them anymore.

@vaporeon_ how would I know, though.

Like yeah, if I accidentally went to glaceoff.social, but

I'm at least vaguely aware I'm going to the site I intend to go to

@The_T The very problem with this is that even you typed correctly glaceon.social, an attacker who controls any computer on the path from your computer to glaceon.social (admittedly, that somewhat limits who can do this attack...), could intercept your connection and direct you to glaceoff.social and your browser wouldn't notice because glaceoff.social is faking glaceon.social's certificate

You could, in advance, revoke the trust in eMudhra's certificate that got compromised, so that any real or fake (it's impossible to distinguish at this point) certificates signed by it no longer are trusted by your browser, and so if an attacker directed you to glaceoff.social, the browser would give you an error message instead of connecting

@vaporeon_ yeah, but at that point I wouldn't know.

@The_T @vaporeon_ vaporeon is explaining to you what you can do so that you would know if it were to happen to you

@The_T @vaporeon_ if you remove the known compurromised root certificates then the browser won't trust certificates signed with them and will give you extremely loud warnings that something is bad and wrong

@aescling @vaporeon_ ohhh

how do I do that then

@The_T @aescling In Firefox? Go to about:preferences -> Privacy and security -> View certificates..., and that will open an interface where you can view all certificates and delete any that you want to

Specifically, the certificates by eMudhra and by Comodo (I am honestly not sure how Comodo is related to this, but the web site that reports this is advising to distrust the Comodo certificate, too...)

@vaporeon_ @The_T in non ESR firefox there's a submenu "Connection security" in Privacy and security, under "Certificates" click "Manage certificates"; by default it shows you certificate authorities, which is what you want here