eMudhra's weak certificate keys: what happened and why it matters

A cybersecurity company just managed to make Google, Apple, Microsoft and Mozilla collectively lose their minds. And all because someone apparently thought the number 4 was a perfectly reasonable encryption key.

What a certificate authority does

For the people who think HTML is a programming language: When you visit a website, your browser checks its security certificate to verify that you're connecting to the genuine server. Companies called Certificate Authorities (CAs) issue these certificates, and eMudhra is one of them.

On October 17, a security researcher alerted Google and Mozilla that eight intermediate certificates belonging to eMudhra had private keys so weak they could be recovered almost instantly.

These certificates were created on April 30, 2025, using P-384 elliptic-curve cryptography.

The eight keys

For context, a properly generated key is selected from an astronomically large range of possible numbers. We're talking roughly 2³⁸⁴ possibilities.

The eight private keys discovered by researchers?

4, 56, 66, 115, 155, 156, 230 and 237.

I'm not kidding. Those were the actual numbers.

All eight could be recovered in less than a second.

Someone could potentially use these keys to forge certificates, impersonate legitimate websites and intercept communications if the affected certificates were still trusted.

Imagine opening what appears to be your bank's website, seeing the reassuring padlock in your browser, and having absolutely no idea that you're talking to an attacker.

And this wasn't some random startup's internal testing environment. These certificates belonged to an authority trusted by major browsers.

How Google, Mozilla, Apple and Microsoft responded

Google received the report at 18:05 UTC on October 17 and had confirmed the problem and deployed a protective block by 19:45 UTC. Good job, Gemini!

Mozilla also blocked the affected certificates that evening. Apple and Microsoft subsequently took protective action as well.

So how on earth did this happen?

According to eMudhra, a flaw during a cryptographic key-generation ceremony produced a second set of weak keys during a wrap/unwrap operation. Those weak keys ended up being published.

The company says its infrastructure wasn't breached, its Indian digital-signature services remain unaffected, and none of the eight intermediates issued certificates to end users.

There is also no confirmed evidence of malicious exploitation.

Which is fortunate, because this could have been spectacularly ugly.

How did this pass two years of audits?

But here's the part that bothers me.

eMudhra says these certificates had passed independent audits for two consecutive years.

TWO YEARS.

We're talking about cryptographic infrastructure where the entire security model depends on generating keys that nobody can realistically guess. And somehow, eight keys smaller than 256 survived the process.

Apparently, someone forgot that the random number generator was supposed to generate random numbers.