Because it was revealed that an actual TLS certificate used the number 4 as a private key.

You may find that answr from another community helpful:
https://feddit.online/comment/10016475

There is a massive security incident this week where an Indian certificate authority used 4 as the private key they used to sign encrypted internet traffic with.

Knowing their secret key lets anyone forge certificates that they can use to snoop on or modify internet traffic.

All 8 of their private keys were under 255, so could be trivially guessed. These certificates were accepted by all major browsers and operating systems, as well as many programming languages and tools.

That was a really good answer actually

I tried to read the comments, but I couldn't get in:

In my defense, the comm is No Stupid Questions, not No Stupid Comments.

because 42 would have been too obvious.

Not just a tls certificate, A root CA certificate trusted by pretty much everything

Amazing. I have the same combination on my luggage.

I'm surrounded by Assholes!

https://arstechnica.com/security/2026/10/the-internet-goes-on-high-alert-after-discovery-of-8-compromised-tls-certs/

It's hard to properly describe how big a fuckup this is. All I will say is that all the coverage I've seen is underselling the potential for harm. There's nothing you can do except update your shit, pray that everyone in the upstream supply chain of every service you use has updated their shit, and take comfort in the fact that there are no proven wild exploits out there (yet).

There are two parts to this answer.

First, as many have pointed out, eMudhra as a trusted certificate authority has issued eight high-level certificates with a key length of onle 3-8 bits, when they should be 384 bits long. And yes, the smallest key was '4'.

But the other point is tha xkcd predicted using 4 as a random number, decades ago. It was supposed to be a joke.

https://xkcd.com/221/

Oh my god, I thought that was a recent meme someone made because of this debacle, didn't know it was an OG xkcd...

An organization trusted with the security of potentially billions of people essentially used the password "4" among other bad choices.

You can read the technical explanation here: https://emudhra.we-have-a-problem.com/

"Lemmeme" tho. 'twas RIGHT there.

But, since nobody would expect an organization like that to have a one digit key, wouldn't that make it extremely hard to guess?

Half kidding here.

Not if you're brute forcing it.

xkcd also happened to release a comic about a "vulnerability in the number 3" the same day the eMudhra news broke.

Well, someone did guess it so it's not that hard. The entropy was really low.

I think it technically was not "brute forcing" (since it wasn't found by searching the entire key space), but specifically someone tried generating CA cert private keys from numbers 0-255, and surprisingly found a few.

Ain’t no way I’m starting from 0 if the standard key is 256-bit

I just dont understand why they would do this? Putting so shitty key is like they wanted to make it as insecure as possible. Even if the ones responsible were criminally stupid, they still should have understood that this is like leaving the whole thing unlocked.

And for such critical thing. Imagine if this wasnt discovered like this but instead by some competent malicious actor that had resources to coordinate some large scale attack and kept it hidden until just the right moment when they can strike at everything.

I also dont understand how little outrage there even is about this, we were really close to huge catastrophe. Or maybe i have misunderstood the severity of what happened.

'Entropy' doesnt apply here

I'm glad I use good ol' 12345!

They are saying there were mistakes made with their key generation scripts:

We have done some preliminary assessment, there appears to be a flaw in the KGC script that was used on that specific day to create these ECC issuers. As for these ECC keys, our review of the KGC, assessment of the code and view of HSM keys so far indicate that a) a set of original ECC keys were created onboard as expected b) an approved deviation to our usual KGC to test a wrap/unwrap was introduced as these keys were meant for export for this instance c) a flaw in the code resulted in the second pair of keys being created onboard which were weaker d) these second pair of weaker keys were used by mistake to create the csr (because the key labels were similar) and signed by our root e) the CSR from these weaker keys were also sent over to Sectigo for cross signing (we verified the files sent over to Sectigo)

Source: https://bugzilla.mozilla.org/show_bug.cgi?id=2083449#c11

Personally I'm still a little confused why it makes any difference that the keys were intended for export to their European and US operations

Nit: That that key doesn’t technically encrypt traffic, if I understand correctly. It’s used to verify the identify of a website. So someone with this private key can’t directly read internet traffic. They can set up a man-in-the-middle attack, but they’d also have to compromise DNS to pull it off.

That's not "happened to"; read the title text if you want to remove all reasonable doubt that it's a reference to it.

Check the alt text on that one :-)

Aw, thanks

Yes, I think you’re correct

It does doesn't it?

The higher the number of bits, the more entropy in the system.

supposed to ...

It’s just as arbitrary as any other number. You can pick at random, but starting with a dictionary attack of easy, non-random keys would probably be a better start.

I remember playing a game of dvd-deal or no deal, where you would pick random number from one to twenty and see if you won money. The people I was playing with were mad because I just started guessing 1, 2, 3, 4…

I told them statistically it was just as likely to be those numbers as anything else.

Interesting question! Google spit this out and it makes sense:

The primary reason these specific keys/issuers were created was to solve data sovereignty and data residency requirements for customers in those regions.

Many European and US corporate clients operate under strict legal frameworks (like GDPR in Europe or various federal compliance standards in the US) that legally dictate where cryptographic infrastructure can live, where data can be decrypted, and who can possess the root or intermediate private keys.

Generating separate regional keys is a compliance mechanism to guarantee that a customer's data or handshake traffic stays within their jurisdiction.

Security by obscurity is what it’s called in the industry, and yeah it’s not a good way to do it. Automation and scripts would make it trivial to guess.

It's kinda like locking your door by putting a wedge in the crack. Probably, no one is going to try to open your door anyways, and probably, even if they did no one is going to take 5 seconds to examine the door and figure it out

But if someone does, it's laughably easy to figure it out

It's a pointlessly obscure way of saying there are more numbers

Its a measure of the randomness of numbers in the system, ie the definition of entropy.

People do use it to sound cool, but this use still fits its mathematic definition.

"Time to brute force this key, I guess I will go get some lun.... What do you mean it's already done? Who uses 4????"

I know. Its still pointlessly obscure

I think they italcized that word because it was sardonic.

Aren't all words you don't understand obscure ?

Entropy is the correct word and is commonly use in cryptography.

Except this is internet and pretty much anybody on the planet could test the security of your doors.

I like the analogy but I think it doesn't really apply when it comes to devices that are connected to the internet.

Its a very simple concept and so there's no reason to give it a scientific name which doesnt mean anything to most people

And by the way I would say that entropy isnt even a useful term here. Entropy is defined as

k ln(O)

where O is the total number of microstates (here the number of unique keys that can be made in the system) and k is the boltzmann constant. For the purpose of brute-force attacks we're interested in the total number of microstates O, and so the logarithmic scaling of entropy isn't meaningful.

So why did it take so long for someone to try it?

Kind of like how you don't expect to walk up to an atm, press 1234, and hope for a million dollars to spit out.

No it absolutely does, the method they used to generate private keys ended up having just 8 shannons of entropy which led to the discovery we are discussing

We don't know whether anyone tried it before April 2025, because that's when the vulnerable certificates were issued. If someone did try it before then, they would not find any certificates (as expected) and probably wouldn't even talk to anyone about it.

It feels like the kind if thing that someone, somewhere would have a script running constantly testing for private keys with low values. That it went 18 months without being found is a miracle!

I think there's a good chance people will be looking for this now so will get caught a lot quicker next time.

I think there’s a good chance people will be looking for this now so will get caught a lot quicker next time.

That's pretty much guaranteed from now on, yes.

It feels like the kind if thing that someone, somewhere would have a script running constantly testing for private keys with low values. That it went 18 months without being found is a miracle!

It's not the kind of thing you'd expect to need to guard against, or even really think of. It should not happen. It sounds like someone was kind of just fooling around with making private keys and stumbled upon it.

I guess now someone needs to try seeding some of the most popular PRNGs with 0-255 and seeing whether any keys come up in the first few hundred numbers.

It’s a little more complex than that. But if you want to encrypt, and you do want your site traffic encrypted, you use site certificate to give the client browser proof that you are who you say you are. You do this by establishing a chain of trust: “I got this proof that I am who I say I am from this major trusted certificate authority” you trust them and they trust me, so we’re all good. You’ve probably seen the warning that a site isn’t secure, and that’s because they let their certificate of trust expire.

This low entropy key means it’s trivial for me to fake that I have that major authority’s trust. The browser needs to be updated to no longer trust that authority. Until it does I can easily fake being anyone and say that compromised site vouches for me. I don’t even need to be a man in the middle, I just need to set up a way that your browser sends you to my fake server instead of the real one. Lots of ways to do that.