Statistics

TLS Certificate

R10

About R10

Operator
Internet Security Research Group (ISRG)
Chains to
ISRG Root X1
Key type
RSA
In use since
2024

Free automated DV TLS via ACME. Most of the free-TLS web chains through a Let's Encrypt intermediate.

Part of the 2024 rotation of RSA intermediates. Rotating intermediates reduces blast radius if a key ever has to be revoked.

Frequently asked questions

Is R10 a legitimate certificate authority?

Yes. R10 is a publicly trusted intermediate CA operated by Internet Security Research Group (ISRG) and chained to ISRG Root X1. It is recognized by all mainstream browsers and operating system trust stores. The certificate itself is not a phishing indicator — the same intermediate signs millions of legitimate sites.

Why does R10 show up on phishing sites?

Internet Security Research Group (ISRG) issues RSA domain-validated certificates automatically and at no cost (or very low cost), which is the exact workflow scammers need to put HTTPS on a throwaway domain. Domain validation only proves that the requester controls the domain name, not that the site behind it is trustworthy. phishunt lists the specific domains currently flagged below — those are the suspicious ones, not R10 itself.

How do I verify a certificate issued by R10?

In a desktop browser, click the padlock in the address bar and open the certificate viewer. Confirm the issuer chain ends at ISRG Root X1, that the subject matches the domain you expect, and that the notAfter date has not passed. A valid R10 certificate only proves TLS was negotiated correctly — always verify the domain name itself belongs to the service you intended to visit.

What is the difference between R10 and R11?

R10 and its siblings (R11, R12, R13, R14) share the same operator (Internet Security Research Group (ISRG)) and roll up to the same root (ISRG Root X1). CAs rotate multiple intermediates so that if one key ever has to be revoked, the damage is contained. As a user, you can treat all of them as the same trust anchor.

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