Overview#Let’s Encrypt is a free, automated, and open Certificate Authority (CA), run for the public’s benefit. Let’s Encrypt is a service provided by the Internet Security Research Group (ISRG).
The key principles behind Let’s Encrypt are:
- Free: Anyone who owns a domain name can use Let’s Encrypt to obtain a trusted certificate at zero cost.
- Automatic: Software running on a web server can interact with Let’s Encrypt to painlessly obtain a certificate, securely configure it for use, and automatically take care of renewal.
- Secure: Let’s Encrypt will serve as a platform for advancing TLS security best practices, both on the CA side and by helping site operators properly secure their servers.
- Transparent: All certificates issued or revoked will be publicly recorded and available for anyone to inspect.
- Open: The automatic issuance and renewal protocol will be published as an open standard that others can adopt.
- Cooperative: Much like the underlying Internet protocols themselves, Let’s Encrypt is a joint effort to benefit the community, beyond the control of any one organization.
We’re sometimes asked why we only offer certificates with ninety-day lifetimes. People who ask this are usually concerned that ninety days is too short and wish we would offer certificates lasting a year or more, like some other CAs do.
Ninety days is nothing new on the Web. According to Firefox Telemetry, 29% of TLS transactions use ninety-day certificates. That’s more than any other lifetime. From our perspective, there are two primary advantages to such short certificate lifetimes:
- They limit damage from key compromise and mis-issuance. Stolen keys and mis-issued certificates are valid for a shorter period of time.
- They encourage automation, which is absolutely essential for ease-of-use. If we’re going to move the entire Web to HTTPS, we can’t continue to expect system administrators to manually handle renewals. Once issuance and renewal are automated, shorter lifetimes won’t be any less convenience than longer ones.