R3 TLS Certificate
Phishing sites using this certificate issuer
About R3
- Operator
- Internet Security Research Group (ISRG)
- Chains to
- ISRG Root X1
- Key type
- RSA
- In use since
- 2020
Let's Encrypt's primary RSA intermediate from 2020 through early 2024 — the issuer behind a very large fraction of the public web's free TLS during that window.
Replaced by the R10-R14 rotation in 2024 but still appears on long-lived certificates issued before then.
Frequently asked questions
Is R3 a legitimate certificate authority?
Yes. R3 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 R3 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 R3 itself.
How do I verify a certificate issued by R3?
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 R3 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 R3 and R10?
R3 and its siblings (R10, R11, R12, R13) 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.
It is strongly recommended to use them for Threat Hunting or add them to a Watchlist.
| Last check (UTC) | First seen (UTC) ▾ | URL | Screenshot | Flags | Details |
|---|
It is strongly recommended to use them for Threat Hunting or add them to a Watchlist.
| URL | Screenshot | Flags | Details |
|---|