Indian certification authority eMudhra’s private keys compromised – one of them was the number ‘4’

Tragically simple private keys used by a certification authority based in India have been compromised, meaning the 60-million-plus certs it has issued can’t be trusted and necessitating a massive clean-up job.

The CA of concern in this case is called eMudhra, which boasts of having issued over 60 million digital certificates to help usher in a world of digital trust.

The company has instead panicked the world.

News of the company’s errors appeared on Tuesday in a post by Dennis Jackson, a member of Mozilla’s cryptography engineering team.

“On Saturday, October 17, at 20:06 UTC, Mozilla received a report from a community member that private keys associated with eight eMudhra intermediate certificates had been compromised,” he wrote. “These keys could allow attackers to issue fraudulent HTTPS certificates for websites they do not control.”

Or as Cloudflare put it, “an attacker can create a forged certificate for any domain and use it to impersonate servers to intercept or modify traffic.”

Jackson has since elaborated on the incident and the response, which has thankfully seen Mozilla, Chrome, and Apple remediate the issue so their browsers won’t rely on the certificates – at least after users install an update. He also reports that eMudhra has revoked the certs, and lists many FOSS projects that have issued updates that mean they won’t recognize certs from eMudhra.

That’s welcome, but sadly certs signed with these private keys are still out there and many services rely on them. Browser makers are set up to detect and reject bad certs. Others who relied on them may not be, and will likely need to dig into their environments to see if they rely on certs signed by eMudhra. Developer Geoffrey Huntley has offered some advice on automating that process.

At the time of writing, eMudhra has not responded to The Register’s inquiries about the incident and its security practices.

The latter question is of great interest because security researcher Scott Helme analyzed eMudhra’s certs and found one the private keys it used “is the number 4.”

“Not a number that starts with 4, or the number 4 followed by a few hundred random digits, just, 4... Another one is 56, and another is 115. I know, because I recovered all of them from their public certificates on my laptop just now, and it took less than a second,” Helme wrote.

Other researchers have found private keys including the numbers 66, 155, 156, 230 and 237.

Those are vastly inadequate keys, because they’re easy to guess, making all certs issued by eMudhra susceptible to brute force attacks.

As Helme put it: “A P-384 private key should be a random 384-bit number, which gives you 2³⁸⁴ possibilities (or roughly 10¹¹⁵), so nobody is ever going to search that.”

This is a developing story and The Register will update it as more information becomes available. ®