Let's Encrypt CA Root Hierarchy Chain Evolution History
2015: Let’s Encrypt Root CA Initial Setup In 2015, Let’s Encrypt have three CA certificates:
ISRG Root X1 Certificate Let’s Encrypt Intermediate X1 CA Certificate Let’s Encrypt Intermediate X2 CA Certificate Let’s Encrypt will issue certificates to subscribers from its intermediate CAs, allowing Let’s Encrypt to keep root CA safely offline. IdenTrust will cross-sign Let’s Encrypt intermediates. This allow our end certificates to be accepted by all major browsers while Let’s Encrypt propagate its own root.