S2S-TLS: Convert SSL.txt to Markdown and update information given

[ngircd-alex.git] / doc / SSL.md

diff --git a/doc/SSL.md b/doc/SSL.md
new file mode 100644 (file)
index 0000000..a2e029b
--- /dev/null
+++ b/doc/SSL.md
@@ -0,0 +1,80 @@
+# [ngIRCd](https://ngircd.barton.de) - SSL/TLS Encrypted Connections
+
+ngIRCd supports SSL/TLS encrypted connections using the *OpenSSL* or *GnuTLS*
+libraries. Both encrypted server-server links as well as client-server links
+are supported.
+
+SSL is a compile-time option which is disabled by default. Use one of these
+options of the ./configure script to enable it:
+
+- `--with-openssl`: enable SSL support using OpenSSL.
+- `--with-gnutls`: enable SSL support using GnuTLS.
+
+You can check the output of `ngircd --version` to validate if your executable
+includes support for SSL or not: "+SSL" must be listed in the feature flags.
+
+You also need a SSL key and certificate, for example using Let's Encrypt, which
+is out of the scope of this document.
+
+From a feature point of view, ngIRCds support for both libraries is
+comparable. The only major difference (at this time) is that ngIRCd with GnuTLS
+does not support password protected private keys.
+
+## Configuration
+
+SSL-encrypted connections and plain-text connects can't run on the same network
+port (which is a limitation of the IRC protocol); therefore you have to define
+separate port(s) in your `[SSL]` block in the configuration file.
+
+A minimal configuration for *accepting* SSL-encrypted client & server
+connections looks like this:
+
+``` ini
+[SSL]
+CertFile = /etc/ssl/certs/my-fullchain.pem
+KeyFile = /etc/ssl/certs/my-privkey.pem
+Ports = 6697, 6698
+```
+
+In this case, the server only deals with *incoming* connections and never has to
+validate SSL certificates itself, and therefore no "Certificate Authorities" are
+needed.
+
+If you want to use *outgoing* SSL-connections to other servers, you need to add:
+
+``` ini
+[SSL]
+...
+CAFile = /etc/ssl/certs/ca-certificates.crt
+DHFile = /etc/ngircd/dhparams.pem
+
+[SERVER]
+...
+SSLConnect = yes
+```
+
+The `CAFile` option configures a file listing all the certificates of the
+trusted Certificate Authorities.
+
+The Diffie-Hellman parameters file `dhparams.pem` can be created like this:
+
+- OpenSSL: `openssl dhparam -2 -out /etc/ngircd/dhparams.pem 4096`
+- GnuTLS: `certtool --generate-dh-params --bits 4096 --outfile /etc/ngircd/dhparams.pem`
+
+Note that enabling `SSLConnect` not only enforces SSL-encrypted links for
+*outgoing* connections to other servers, but for *incoming* connections as well:
+If a server configured with `SSLConnect = yes` tries to connect on a plain-text
+connection, it won't be accepted to prevent data leakage! Therefore you should
+set this for *all* servers you expect to use SSL-encrypted connections!
+
+## Accepting untrusted Remote Certificates
+
+If you are using self-signed certificates or otherwise invalid certificates,
+which ngIRCd would reject by default, you can force ngIRCd to skip certificate
+validation on a per-server basis and continue establishing outgoing connections
+to the respective peer by setting `SSLVerify = no` in the `[SERVER]` block of
+this remote server in your configuration.
+
+But please think twice before doing so: the established connection is still
+encrypted but the remote site is *not verified at all* and man-in-the-middle
+attacks are possible!