There's no easy way to "just" transmit data in a foolproof manner. You practically need to support CSRs as a CA anyway, so you might as well use the existing ASN.1+X509 system to transmit data.

ASN.1 and X509 aren't all that bad. It's a comprehensively documented binary format that's efficient and used everywhere, even if it's hidden away in binary protocols you don't look at every day.

Unlike what most people seem to think, ACME isn't something invented just for Let's Encrypt. Let's Encrypt was certainly the first high-profile CA to implement the protocol, but various CAs (free and paid) have their own ACME servers and have had them for ages now. It's a generic protocol for certificate authorities to securely do domain validation and certificate provisioning that Let's Encrypt implemented first.

The unnecessarily complex parts of the protocol when writing a from-the-ground-up client are complex because ACME didn't reinvent the wheel, and reused existing standard protocols instead. Unfortunately, that means having to deal with JWS, but on the other hand, it means most people don't need to write their own ACME-JWS-replacement-protocol parsers. All the other parts are complex because the problem ACME is solving is actually quite complex.

The author wrote [another post](https://rachelbythebay.com/w/2023/01/03/ssl/) about the time they fell for the lies of a CA that promised an "easier" solution. That solution is pretty much ACME, but with more manual steps (like registering an account, entering domain names).

I personally think that for this (and for many other protocols, to be honest) XML would've been a better fit as its parsers are more resilient against weird data, but these days talking about XML will make people look at you like you're proposing COBOL. Hell, I even exchanging raw, binary ASN.1 messages would probably have gone over pretty well, as you need ASN.1 to generate the CSR and request the certificate anyway. But, people chose "modern" JSON instead, so now we're base64 encoding values that JSON parsers will inevitably fuck up instead.

> Unlike what most people seem to think, ACME isn't something invented just for Let's Encrypt. Let's Encrypt was certainly the first high-profile CA to implement the protocol, but various CAs (free and paid) have their own ACME servers and have had them for ages now. It's a generic protocol for certificate authorities to securely do domain validation and certificate provisioning that Let's Encrypt implemented first.

This depends on whether you're speaking as a matter of history. ACME was originally invented and implemented by the Let's Encrypt team, but in the hope that it could become an open standard that would be used by other CAs. That hope was eventually borne out.

The described protocol looks like rewording of X509 with json syntax, but you still have X509, as a result you have two X509. Replay nonce is used straightforwardly as serial number, termsOfServiceAgreed can be extension, and CSR is automatically signed in the process of generation.