Let’s Encrypt, a publicly trusted certificate authority (CA) that Cloudflare uses to issue TLS certificates, has been relying on two distinct certificate chains. One is cross-signed with IdenTrust, a globally trusted CA that has been around since 2000, and the other is Let’s Encrypt’s own root CA, ISRG Root X1. Since Let’s Encrypt launched, ISRG Root X1 has been steadily gaining its own device compatibility.

On September 30, 2024, Let’s Encrypt’s certificate chain cross-signed with IdenTrust will expire. To proactively prepare for this change, on May 15, 2024, Cloudflare will stop issuing certificates from the cross-signed chain and will instead use Let’s Encrypt’s ISRG Root X1 chain for all future Let’s Encrypt certificates.

The change in the certificate chain will impact legacy devices and systems, such as Android devices version 7.1.1 or older, as those exclusively rely on the cross-signed chain and lack the ISRG X1 root in their trust store. These clients may encounter TLS errors or warnings when accessing domains secured by a Let’s Encrypt certificate.

According to Let’s Encrypt, more than 93.9% of Android devices already trust the ISRG Root X1 and this number is expected to increase in 2024, especially as Android releases version 14, which makes the Android trust store easily and automatically upgradable.

We took a look at the data ourselves and found that, from all Android requests, 2.96% of them come from devices that will be affected by the change. In addition, only 1.13% of all requests from Firefox come from affected versions, which means that most (98.87%) of the requests coming from Android versions that are using Firefox will not be impacted.

Preparing for the change

If you’re worried about the change impacting your clients, there are a few things that you can do to reduce the impact of the change. If you control the clients that are connecting to your application, we recommend updating the trust store to include the ISRG Root X1. If you use certificate pinning, remove or update your pin. In general, we discourage all customers from pinning their certificates, as this usually leads to issues during certificate renewals or CA changes.

If you experience issues with the Let’s Encrypt chain change, and you’re using Advanced Certificate Manager or SSL for SaaS on the Enterprise plan, you can choose to switch your certificate to use Google Trust Services as the certificate authority instead.

For more information, please refer to our developer documentation.

While this change will impact a very small portion of clients, we support the shift that Let’s Encrypt is making as it supports a more secure and agile Internet.

Embracing change to move towards a better Internet

Looking back, there were a number of challenges that slowed down the adoption of new technologies and standards that helped make the Internet faster, more secure, and more reliable.

For starters, before Cloudflare launched Universal SSL, free certificates were not attainable. Instead, domain owners had to pay around $100 to get a TLS certificate. For a small business, this is a big cost and without browsers enforcing TLS, this significantly hindered TLS adoption for years. Insecure algorithms have taken decades to deprecate due to lack of support of new algorithms in browsers or devices. We learned this lesson while deprecating SHA-1.

Supporting new security standards and protocols is vital for us to continue improving the Internet. Over the years, big and sometimes risky changes were made in order for us to move forward. The launch of Let’s Encrypt in 2015 was monumental. Let’s Encrypt allowed every domain to get a TLS certificate for free, which paved the way to a more secure Internet, with now around 98% of traffic using HTTPS.

In 2014, Cloudflare launched elliptic curve digital signature algorithm (ECDSA) support for Cloudflare-issued certificates and made the decision to issue ECDSA-only certificates to free customers. This boosted ECDSA adoption by pressing clients and web operators to make changes to support the new algorithm, which provided the same (if not better) security as RSA while also improving performance. In addition to that, modern browsers and operating systems are now being built in a way that allows them to constantly support new standards, so that they can deprecate old ones.

For us to move forward in supporting new standards and protocols, we need to make the Public Key Infrastructure (PKI) ecosystem more agile. By retiring the cross-signed chain, Let’s Encrypt is pushing devices, browsers, and clients to support adaptable trust stores. This allows clients to support new standards without causing a breaking change. It also lays the groundwork for new certificate authorities to emerge.

Today, one of the main reasons why there’s a limited number of CAs available is that it takes years for them to become widely trusted, that is, without cross-signing with another CA. In 2017, Google launched a new publicly trusted CA, Google Trust Services, that issued free TLS certificates. Even though they launched a few years after Let’s Encrypt, they faced the same challenges with device compatibility and adoption, which caused them to cross-sign with GlobalSign’s CA. We hope that, by the time GlobalSign’s CA comes up for expiration, almost all traffic is coming from a modern client and browser, meaning the change impact should be minimal.