I’m exploring the use of Let’s Encrypt in our environment. As part of our internal governance requirements, we conduct a thorough security review for any product or service before adoption.
I would appreciate guidance from the community on how best to approach a security review for Let’s Encrypt.
Specifically, I’m looking to understand:
What is the recommended approach or methodology for performing a security review of Let’s Encrypt?
Are there any official security documents, architecture diagrams, or threat models available for reference?
What are the key security considerations, common pitfalls, or areas that require particular attention (e.g., certificate issuance, validation mechanisms, key management, API usage)?
Additionally, if there are any published security assessments, best practices, or community guidelines related to secure adoption, I would greatly appreciate links or references.
Thank you in advance for your guidance and support.
If you want high security, protect your domain with DNSSEC and a CAA record where the CAA record includes validationmethods=dns-01 and/or accounturi.
Other validation methods are available and can be included in the CAA record however they're susceptible to MitM attacks which can be prevented by specifying the account uris permitted to get certificates for your domain (one account per CAA record).
I think a lot depends on what exactly you're reviewing. Are you talking about enabling Let's Encrypt as a CA your user systems trust (which most operating systems and browsers trust by default, but some places might be more strict)? Are you talking about becoming a Let's Encrypt subscriber to request certificates for use on your servers? What kind of threats are you trying to tell if using Let's Encrypt's services in some fashion can help you defend against in some way?
All of those aren't really any different with Let's Encrypt than with any other CA. I suppose for ACME-based CAs like Let's Encrypt you have to consider your account key management in addition to your certificate key management, but really again there isn't anything specific to Let's Encrypt there.
You certainly want to be aware of the rate limits, but they're generally pretty generous.
I'd like to add that Let's Encrypt never sees your private keys. This is not unique to Let's Encrypt, however it might be useful to know this when comparing Let's Encrypt against a CA which does handle your private keys.
We plan to initially leverage Let’s Encrypt for internal services and automate the certificate lifecycle. Any internal service requiring an SSL/TLS certificate will be able to request it, enabling automated issuance as well as deployment to the target environment. The future depends on the experience. Thank your for suggestions around ACME based enrollment and rate limits.