Freenode SASL Upgrade: Irssi HOWTO

Mon 01/05/15   12:25  in  technical

The freenode [1] IRC network has for a long time supported connecting and automatic identification using SASL [2].

Recently, the freenode network deprecated the commonly used SASL mechanism DH-BLOWFISH due to security concerns, causing my IRC client (irssi [3]) to no longer be able to authenticate.

Unfortunately, while scripts and guides describing using irssi with DH-BLOWFISH are plentiful, it seems the steps required to use the new preferred ECDSA-NIST256P-CHALLENGE method are not yet documented.

Read on for a step-by-step walk-through of configuring irssi to use SASL with freenode in 2015.


Recently freenode upgraded to Atheme 7.2 [4], and in the process deprecated support for the SASL mechanism DH-BLOWFISH. Atheme is the reference implementation of the current IRC protocol, which deprecates DH-BLOWFISH in IRCv3 [5].

There are good reasons for this change, but regardless it’s been done and irssi needs some help accommodating this change.

Why not PLAIN?

It would be remiss not to mention that the simplest solution to this problem is to use the PLAIN SASL method in conjunction with SSL. Clients configured in this way will work with the new services just like they have previously, with similar security properties.

While it is not my goal to convince you PLAIN is insufficient, there is benefit in using a SASL method other than PLAIN in a defense-in-depth sort of way. Should the SSL stream become compromised in some manner, PLAIN would make obtaining a user’s password as easy as forcing a reconnect, while the other mechanisms provide additional layers of security.

Use SSL!

Regardless of the SASL method being used, if you’re bothering with any of this the first and most effective step to securing your IRC connection is using SSL. SSL is supported by virtually all IRC networks and requires only trivial configuration in most clients.

Be sure your client validates the server’s certificate properly (strict SSL) or your connection is trivially vulnerable to MITM [6] attacks.

Why SASL in addition to SSL

Common implementations give SASL users one benefit not generally available to other users: with SASL, network services recognize you before you even are active on the network, which can be useful when making use of services like a hostname cloak or automatically joining channels only open to invited accounts.

As an aside, as far as I can tell client-side certificates (like those used with CertFP [7] identification) could be used to provide similar benefits but this doesn’t seem to be done on any network I’m familiar with. One possible explanation is that since CertFP doesn’t work with Tor (I believe?), implementation efforts focus on SASL which is available to all users.

Other reasons include additional layers of security in terms of protecting the account password, and policies such as freenode’s requirement of SASL when connecting over Tor [8].

Configuring Irssi to use ECDSA-NIST256p-CHALLENGE

1) Install ecdsatool

First, download and build a copy of ecdsatool [9]. This wasn’t available as a package for my server’s distribution, so I built is as follows:

$ git clone
$ cd ecdsatool
$ ./
$ ./configure --prefix=$HOME/local
$ make -j
$ make install

Standard build recipe, tweak as you see fit.

Afterwards, be sure the resulting ecdsatool utility is available on your shell’s PATH so the irssi script we configure later will be able to find and use it.

2) Generate key pair

Next, use ecdsatool to generate a key pair for SASL use:

$ mkdir -p ~/.irssi/certs
$ ecdsatool keygen ~/.irssi/certs/freenode.pem

I keep my IRC-related certificates in ~/.irssi/certs, personal preference.

3) Install cap_sasl script

Next, grab a copy of the script shipped in the ecdsatool repository:

$ mkdir -p ~/.irssi/scripts
$ wget -O ~/.irssi/scripts/

Additionally you likely want to have the script loaded when irssi starts:

$ mkdir -p ~/.irssi/scripts/autorun
$ ln -s ../ ~/.irssi/scripts/autorun/

4) Configure SASL for freenode

From within irssi, use the /sasl set command to indicate what username and certificate to use for your IRC network:

$ irssi
/sasl set freenode username /full/path/to/freenode.pem ECDSA-NIST256P-CHALLENGE

Replacing freenode with the network name your configured in irssi, username with your freenode account name, and the path with a full path to the key pair generated earlier.

Afterwards, be sure to save this information for future use:

/sasl save

The result should be an entry in ~/.irssi/sasl.auth that looks something like this:

freenode dtzWill /home/will/.irssi/certs/freenode.pem ECDSA-NIST256P-CHALLENGE

5) Register Public Key with NickServ

Almost there! Final step is to give NickServ the public key portion of our key pair so it can recognize your client and associate it with your account.

First, grab the pubkey from the key pair:

$ ecdsatool pubkey ~/.irssi/certs/freenode.pem

Next, connect to freenode and identify yourself as you would usually.

Finally, tell NickServ about your public key:

/msg nickserv set property pubkey ArRZ4XCwSFYhT7RH5Ms7dosJEm8OYLO3gWSSGQCsYOCk

Replacing the example public key with what was printed by ecdsatool in the previous step.

6) Done! Reconnect and Test

At this point you have all the pieces required to use SASL with the ECDSA-NIST256P-CHALLENGE mechanism to connect to freenode. Disconnect from freenode and reconnect to try it out!

If successful, you should see something like this:

14:50 -!- Irssi: CLICAP: supported by server: account-notify extended-join identify-msg multi-prefix sasl
14:50 -!- Irssi: CLICAP: requesting: multi-prefix sasl
14:50 -!- Irssi: CLICAP: now enabled: multi-prefix sasl
14:50 -!- will!will@unaffiliated/dtzwill dtzWill You are now logged in as dtzWill.
14:50 -!- Irssi: SASL authentication successful

Alternative Method Without ecdsatool

It appears that there is another solution that does not require the use of an external tool like ecdsatool by using the Crypt::PK::ECC perl module.

This script is available in the Atheme git repository: git [10]. In addition to no longer requiring an external tool, the script offers a keygen command that should make setup easier.

I haven’t tried this script yet myself, as I didn’t discover it until well after I completed the procedure described above. Additionally, the module is uses doesn’t seem to be available as a package on any of my systems although it can of course be obtained using cpan [11].

If you try this method and have success, please report back.

(Update: March 03, 2015)

Jesper Freesbug from the comments was kind enough to share his experiences and provide a walkthrough of the setup process when using this approach. I’ve featured this comment below and recommend taking a look if you’re interested in this solution.

In addition to the FreeBSD package he mentions, it seems other systems also provide the required perl module as part of a cryptx package. For example, on Arch it’s available as an AUR package named perl-cryptx. Hopefully the module is made more universally available in the future.

Closing Thoughts

It seems the folks working on Atheme and freenode are hard at work improving the services that are widely used in a variety of communities. While this post is motivated by a lack of documentation, the procedure is simple and it has been mentioned in multiple places time that they hope to both document this thoroughly soon and to improve the workflow for users. Huge thanks to those folks, and for offering all of this work for free for users like myself to enjoy.

Additionally, all of this is arguably something an IRC client should support natively or at least help facilitate. This is how some folks feel and have opened an issue on the irssi github [12].

Hope this helps, and let me know if you have any questions or issues. Enjoy!

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