Specify TLSv1.3 Cipher Suites

[inoblue]

1. Caddy version (caddy version):

v2.4.3 h1:Y1FaV2N4WO3rBqxSYA8UZsZTQdN+PwcoOcAiZTM8C0I=

2. How I run Caddy:

a. System environment:

OS: Debian bullseye amd64
Kernel: 5.10.0-7

b. Command:

Use systemd to start caddy.

c. Service/unit/compose file:

This is the systemd service file.

[Unit]
Description=caddy
After=network-online.target
[Service]
ExecStart=/usr/bin/caddy run --config /path/to/Caddyfile
[Install]
WantedBy=multi-user.target

d. My complete Caddyfile or JSON config:

Since the question is only related to TLS, I hide the domain.

example.com
root * /path/to/html
tls /path/to/cert.crt /path/to/priv.key {
	protocols tls1.3
	curves x25519
}
file_server

3. The problem I’m having:

In the document, it says cipher suites are not customizable for TLS 1.3. I wonder is there a way to specify TLSv1.3 cipher suites for caddy? For example, specify that only TLS_AES_128_GCM_SHA256 is accepted. When using Apache and Nginx, which are based on OpenSSL, you can specify TLSv1.3 cipher suites by changing OpenSSL config /usr/lib/ssl/openssl.cnf. I want to know if there is also a similar way to do that in caddy.

4. Error messages and/or full log output:

5. What I already tried:

I tried to change OpenSSL config, but of course it doesn’t work since caddy uses Go’s TLS.

6. Links to relevant resources:

[francislavoie]

@inoblue

In the document, it says cipher suites are not customizable for TLS 1.3. I wonder is there a way to specify TLSv1.3 cipher suites for caddy?

No. Cipher suites for TLS 1.3 are set in stone. We use Go’s stdlib for TLS facilities, and it doesn’t allow configuring cipher suites, because from a security perspective, it’s a risk to allow users to potentially shoot themselves in the foot.