Ten years ago, we printed one of the nerdiest t-shirts we’ve ever made. On the front was the entire PEM encoding of ISRG Root X1 in base64. Back then, it represented a future we were working toward. Today, that same design tells the story of just how far Let’s Encrypt has come. Let’s Encrypt was already issuing publicly trusted certificates in 2016, but ISRG Root X1 itself was still slowly and qui…
Let’s Encrypt is committed to a post-quantum-safe Web PKI. The path we’re planning to take is Merkle Tree Certificates (“MTCs”), a new approach that adds post-quantum authentication to the web without sacrificing the speed and reliability that have made TLS universal. This post is about these plans and why we believe MTCs are worth pursuing as a key to a post-quantum future. An increasingly urgent…
Have you ever needed to make sure your website has a broken certificate? While many tools exist to help run an HTTPS server with valid certificates, there aren’t tools to make sure your certificate is revoked or expired. This is not a problem most people have. Tools to help manage certificates are always focused on avoiding those problems, not creating them. Let’s Encrypt is a Certificate Authorit…
Nick Silverman is a Senior Infrastructure Engineer on the Edge Infrastructure team at Shopify, where he maintains the systems that provision, renew, and publish SSL certificates for millions of merchants’ custom domains. He is also a contributor to the Ruby acme-client gem. The challenge Shopify’s automated certificate management system relied on a static renewal threshold: 30 days before the end…
This was also posted on EFF’s blog. As we announced earlier this year, Let’s Encrypt now issues IP address and six-day certificates to the general public. The Certbot team at the Electronic Frontier Foundation has been working on two improvements to support these features: the --preferred-profile flag released last year in Certbot 4.0, and the --ip-address flag, new in Certbot 5.3. With these impr…
As previously announced, over the next two years we will be switching the default certificate lifetime from 90 days to 64 days, and then 45 days. This will ultimately double the number of certificate renewal requests each day: today we expect renewal around day 60 (of a 90-day certificate), while in the future we expect renewal around day 30 (of a 45-day certificate). If you use an ACME client tha…
When you request a certificate from Let’s Encrypt, our servers validate that you control the hostnames in that certificate using ACME challenges. For subscribers who need wildcard certificates or who prefer not to expose infrastructure to the public Internet, the DNS-01 challenge type has long been the only choice. DNS-01 works well. It is widely supported and battle-tested, but it comes with oper…
In a recent conversation with a Let’s Encrypt subscriber, we asked them to guess how many people work at ISRG, the nonprofit behind Let’s Encrypt (and Prossimo and Divvi Up). Their guess was about 100; they’d overestimated by 72.5 people. We’re a pretty small team, and we get a lot done, but most of that work is entirely remote, distributed, and automated. That is a big part of what makes FOSDEM s…
Update: March 11, 2026 If you use Certbot, see Six-Day and IP Address Certificates Available in Certbot for details on requesting these certificates. Short-lived and IP address certificates are now generally available from Let’s Encrypt. These certificates are valid for 160 hours, just over six days. In order to get a short-lived certificate subscribers simply need to select the ‘shortlived’ certi…
This letter was originally published in our 2025 Annual Report. This year was the 10th anniversary of Let’s Encrypt. We’ve come a long way! Today we’re serving more than 700 million websites, issuing ten million certificates on some days. Most importantly, when we started 39% of page loads on the Internet were encrypted. Today, in many parts of the world, over 95% of all page loads are encrypted.…
On September 14, 2015, our first publicly-trusted certificate went live. We were proud that we had issued a certificate that a significant majority of clients could accept, and had done it using automated software. Of course, in retrospect this was just the first of billions of certificates. Today, Let’s Encrypt is the largest certificate authority in the world in terms of certificates issued, the…
Let’s Encrypt will be reducing the validity period of the certificates we issue. We currently issue certificates valid for 90 days, which will be cut in half to 45 days by 2028. This change is being made along with the rest of the industry, as required by the CA/Browser Forum Baseline Requirements, which set the technical requirements that we must follow. All publicly-trusted Certificate Authoriti…
In a ceremony held in September, Let’s Encrypt generated two new Root Certification Authorities (CAs) and six new Intermediate CAs, which we’re collectively calling the “Generation Y” hierarchy. Now we’re moving to begin issuing certificates from this new hierarchy, and to submit it to various root programs for inclusion in their trust stores. The two new roots look very similar to our existing ro…
Seth Schoen was an early contributor to Let's Encrypt through his work at the Electronic Frontier Foundation. He's also one of the longest standing participants in the Let's Encrypt community support forum, so we asked him to offer his thoughts on the role and impact of the forum as a resource for our users. Thank you for your many years of expertise and participation, Seth! — Josh Aas, Head of Le…
Let’s Encrypt has been proud to work with the IETF to maintain ACME as an open standard since we first developed the technology a decade ago. We’re happy to announce that IETF has published our latest addition to the ACME protocol, ACME Renewal Information (ARI), as RFC 9773. ARI helps keep the renewal process reliable during unexpected events affecting certificate validity. Since the ACME protoco…
NGINX and Let's Encrypt share a common vision of an open and secure web. Now, with built-in support for ACME, the world's most popular web server, reverse proxy and ingress controller for Kubernetes can simplify certificate management for everyone. From the home lab to scaled-out, mission-critical enterprise deployments. — Liam Crilly, Sr Dir, Product Management, F5 NGINX Our ideal has always been…
Update, August 18, 2025 We have updated the read-only and shutdown dates to ensure that our new Static CT API logs are fully trusted by browsers before switching Oak to read-only in order to avoid any disruption. Let’s Encrypt operates two types of Certificate Transparency (“CT”) logs—some implement the original RFC 6962 API, and some that implement the newer Static CT API. Today we are announcing…
Today we turned off our Online Certificate Status Protocol (OCSP) service, as announced in December of last year. We stopped including OCSP URLs in our certificates more than 90 days ago, so all Let’s Encrypt certificates that contained OCSP URLs have now expired. Going forward, we will publish revocation information exclusively via Certificate Revocation Lists (CRLs). We ended support for OCSP pr…
Update: January 15, 2026 Six-day and IP address certificates are now generally available. See 6-day and IP Address Certificates are Generally Available for details. Since Let’s Encrypt started issuing certificates in 2015, people have repeatedly requested the ability to get certificates for IP addresses, an option that only a few certificate authorities have offered. Until now, they’ve had to look…
Since its inception, Let’s Encrypt has been sending expiration notification emails to subscribers that have provided an email address to us via the ACME API. This service ended on June 4, 2025. The decision to end the service is the result of the following factors: Over the past 10 years more and more of our subscribers have been able to put reliable automation into place for certificate renewal.…
The Certificate Transparency ecosystem has been improving transparency for the web PKI since 2013. It helps make clear exactly what certificates each certificate authority has issued and makes sure errors or compromises of certificate authorities are detectable. Let’s Encrypt participates in CT both as a certificate issuer and as a log operator. For the past year, we’ve also been running an experi…
Every night, right around midnight (mainly UTC), a horde of zombies wakes up and clamors for … digital certificates! The zombies in question are abandoned or misconfigured Internet servers and ACME clients that have been set to request certificates from Let’s Encrypt. As our certificates last for at most 90 days, these zombie clients’ software knows that their certificates are out-of-date and need…
At Let’s Encrypt we know that building a secure Internet isn’t just a technical challenge—it’s a long-term commitment. Over the past decade we’ve made enormous strides: from issuing billions of TLS certificates to continually innovating to keep the web safer and more accessible. But none of this would be possible without recurring donations from individuals and organizations around the world. Recu…
Update March 16, 2026: Thanks to some timeline changes in the root program requirements, we have been able to push back the removal of the tlsclient profile slightly. If you are already using the tlsclient profile before May 13, 2026, now you will be able to continue to do so through July 8, 2026. Let’s Encrypt will no longer include the “TLS Client Authentication” Extended Key Usage (EKU) in our…
How Pebble Supports ACME Client Developers Together with the IETF community, we created the ACME standard to support completely automated certificate issuance. This open standard is now supported by dozens of clients. On the server side, did you know that we have not one but two open-source ACME server implementations? The big implementation, which we use ourselves in production, is called Boulder…
As we touched on in our first blog post highlighting ten years of Let’s Encrypt: Just as remarkable to us as the technical innovations behind proliferating TLS at scale is the sustained generosity we have benefited from throughout our first decade. With that sense of gratitude top of mind, we are proud to announce a contribution of $1,000,000 from Jeff Atwood. Jeff has been a longtime supporter of…
Earlier this year we announced our intention to introduce short-lived certificates with lifetimes of six days as an option for our subscribers. Yesterday we issued our first short-lived certificate. You can see the certificate at the bottom of our post, or here thanks to Certificate Transparency logs. We issued it to ourselves and then immediately revoked it so we can observe the certificate’s who…
2025 marks ten years of Let’s Encrypt. Already this year we’ve taken steps to continue to deliver on our values of user privacy, efficiency, and innovation, all with the intent of continuing to deliver free TLS certificates to as many people as possible; to deliver encryption for everybody. And while we’re excited about the technical progress we’ll make this year, we’re also going to celebrate thi…
Let’s Encrypt protects a vast portion of the Web by providing TLS certificates to over 550 million websites—a figure that has grown by 42% in the last year alone. We currently issue over 340,000 certificates per hour. To manage this immense traffic and maintain responsiveness under high demand, our infrastructure relies on rate limiting. In 2015, we introduced our first rate limiting system, built…
Since its inception, Let’s Encrypt has been sending expiration notification emails to subscribers that have provided an email address to us. We will be ending this service on June 4, 2025. The decision to end this service is the result of the following factors: Over the past 10 years more and more of our subscribers have been able to put reliable automation into place for certificate renewal. Prov…