Although IRC is useful, the default IRC protocol is unencrypted, which means that anyone listening to your network traffic, such as a black hat sniffing WiFi packets in the same coffee shop as us, or perhaps an unscrupulous Three-Letter Agency or Internet Service Provider, is able to read, and possibly modify, the contents of our messages. In order to defend against this, you can use SSL/TLS on top of the IRC protocol in order to connect securely.
SSL/TLS is poorly-named; the short story is that SSL (Secure Sockets Layer) refers to a now-obsolete version of the encryption protocol while TLS (Transport Layer Security) refers to a new version of the protocol. However, because of the naming kerfuffle, libraries that implement the newer TLS protocol still use the old SSL in their name, such as in the case of the OpenSSL library, which is often used for TLS. The encryption protocol will be referred to in this document as TLS.
TLS makes use of a type of cryptography known as public/private key cryptography. In its most basic form, each user has a pair of keys, one public, and one private. A single user will share their public key and keep secret their private key. The user will thus acquire many public keys and have one private key.
Alas, TLS is not quite so straight-forward with it’s naming, so instead of public keys it has certificates (more formally, “X.509” certificates), which are (very roughly) analogous to public keys. A full discussion of TLS and its X.509 certificates is out of the scope of this document.
Verify Server to the Client
When you connect using TLS, the server will send you a certificate which must
be verified by your machine. By default, this verification is done against a
set of certificates known as the PKI (Public Key
is probably the same set of certificates that your browser uses for
verification. In order to use this with
/server add -ssl_verify chat.freenode.net 6697
irssi to verify the server’s certificate against the
PKI. Note also that the command uses port 6697 rather than 6667, because
the TLS version of the protocol usually runs on a different port. You should
now be able to connect to Freenode securely!
Verify Client to the Server (Optional)
This is an optional step that is useful if you do not wish to send your password to NickServ in order to identify to your account.
This is a bit more tricky, because we need to securely create a public/private
key pair and tell
irssi where they are. The most obvious place to store these
is in your
irssi configuration directory, run:
$ mkdir ~/.irssi/freenode $ cd ~/.irssi/freenode
Next, generate the private key:
$ umask 0077 $ openssl genrsa -out key.pem 4096
This will generate a private key file called
key.pem. Now use the private
key to create a self-signed cerificate:
$ openssl req -x509 -key key.pem -sha256 -out cert.pem -days 7200
This command will prompt you for metadata about yourself: the only field worth
filling out is the “Common Name” field, for which you should put your IRC
nickname. After filling the fields out, you should have a certificate named
cert.pem. Now you can tell
irssi to use this cert and key when you connect
by starting up
irssi and running:
/server add -ssl_cert ~/.irssi/freenode/cert.pem -ssl_pkey ~/.irssi/freenode/key.pem chat.freenode.net 6697
Using a self-signed certificate works in this case because Freenode doesn’t
verify the certificate against the PKI; however, since anyone can create a
certificate, this isn’t very useful for identification purposes, thus we can
only use this for identification by first identifying ourself to NickServ and
then telling NickServ to trust the certificate’s fingerprint. After
connecting to Freenode using
/msg NickServ identify YOURPASSWORD /msg NickServ CERT ADD
This will tell NickServ to add the fingerprint of the certificate that you used to connect with to its database of trusted certificates for your account, thus when you connect with your certificate in the future you will be automatically identified!
This has been an extremely brief introduction to using TLS with Freenode IRC. You should now be able to connect securely to Freenode over TLS, and be able to identify yourself to NickServ without providing your account password.