SSL client certificates

SSL client certificates allow us to identify you by your certificate's fingerprint. This is a cryptographically secure way to identify people (well, at least certificates that belong to people) so that channel owership and access control isn't as hard anymore as it used to be back when the only access control mechanism in IRC were hostmasks.

It also allows us to have service-like channel registration without actually running a services package, i.e. no service-like bots like NickServ, ChanServ etc. exist on this network.

Getting started

You will need to generate a SSL private key and certificate (a self-signed one will do, so you won't even have to deal with certification authorities, however if you use S/MIME for encrypting or signing e-mail, you can also just reuse the private key and certificate and save yourself some time).

You can either use openssl(1) (should be available just about everywhere) or you can use certtool(1) from the gnutls package (gnutls-bin on debian). We will use openssl because it is assumed to be more widespread.

$ openssl genrsa -out key.pem 4096 # generate the private key
$ openssl req -new -x509 -key key.pem -out cert.pem -days 1095 # and the certificate

During the certificate creation process, openssl will ask you a couple of questions. If you don't know the answer to those, just leave them blank and press enter to use the default value since the IRC server does not validate them anyway.

This process will generate a private RSA key with a length of 4096 bits and a certificate that will be valid for 1095 days, which is 3 years. You can replace the number by a higher one or leave -days x out entirely as you deem fit to make your certificate valid until the end of time or SSL, whichever comes first.

You can also adjust the key size, i.e. replace the 4096 by a different number but please note that keys smaller than 2048 bits are considered unsafe by modern standards and keys greater than 8192 might not work with all software (in particular, Apple computers seem to have a problem with them).

UNIX-like operating systems like Linux, *BSD and Mac OS X typically have the openssl commandline tool already installed.

Windows users will need to download the OpenSSL Win32 binaries or Microsoft's makecert.exe (which is part of Microsoft Visual C++) and use the Windows command prompt to generate certificates since Windows itself does not ship a tool for generating certificates. Alternatively, it is also possible to generate certificates using IIS.

Verifying that your certificate works

Assuming you already configured your IRC client to use the certificate according to the client specific instructions and reconnected (because the certificate is only transmitted when a connection is made), you can /whois your own nick to verify if it worked. If you see something like this

* is using a secure connection
* has client certificate fingerprint 0847d42c2c266bb9faaff55320c5a453a71fac43

in the whois output, this means that your attempt at installing a client certificate was successful.

You can also find out about your own certificate's fingerprint by using the openssl command mentioned above:

$ openssl x509 -noout -in path/to/cert.pem -fingerprint -sha1
SHA1 Fingerprint=08:47:D4:2C:2C:26:6B:B9:FA:AF:F5:53:20:C5:A4:53:A7:1F:AC:43

This also works if you concatenated your certificate and private key into a single file, the way irssi and some other IRC clients require it, so there's no need to keep the certificate file around separately.

Please note that you need to strip all colons from this value to format it in a way the IRC server can use it for features like auto-op:

$ openssl x509 -noout -in path/to/cert.pem -fingerprint -sha1 | sed 's/.*=//;s/://g'

This way you can easily copy-paste it whenever you need it.

Using the certificate fingerprint to automatically set modes

This is described in a separate article.