TLS Ciphers and protocols

You can configure the permitted SSL/TLS protocols and ciphers using set::tls::protocols, set::tls::ciphers and set::tls::options::ciphersuites. Or, if you want to override these global options, then you can use listen::tls-options or link::tls-options for listen- and link-specific configuration.

We do our best to ship with secure defaults for these settings. More important for a server is to actually use a real certificate, like from Let's Encrypt.

Default configuration

The default configuration in UnrealIRCd 6.0.5 and later looks like this:

set {
    tls {
        protocols "TLSv1.2,TLSv1.3";
        ciphers "EECDH+CHACHA20 EECDH+AESGCM EECDH+AES+SHA384 EECDH+AES+SHA256";
        ciphersuites "TLS_CHACHA20_POLY1305_SHA256:TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256:TLS_AES_128_CCM_8_SHA256:TLS_AES_128_CCM_SHA256";
        ecdh-curves "x25519:secp521r1:secp384r1:prime256v1";
    }
}

NOTE: There is no need to copy-paste this to your config file as this is already the default!

Result

With OpenSSL 3.0.7 on the server side, this results in the following testssl output:

 Testing server preferences 

 Has server cipher order?     yes (OK) -- TLS 1.3 and below
 Negotiated protocol          TLSv1.3
 Negotiated cipher            TLS_CHACHA20_POLY1305_SHA256, 253 bit ECDH (X25519)
 Cipher order
    TLSv1.2:   ECDHE-ECDSA-CHACHA20-POLY1305 ECDHE-ECDSA-AES256-GCM-SHA384
               ECDHE-ECDSA-AES128-GCM-SHA256 ECDHE-ECDSA-AES256-SHA384 ECDHE-ECDSA-AES128-SHA256 
    TLSv1.3:   TLS_CHACHA20_POLY1305_SHA256 TLS_AES_256_GCM_SHA384 TLS_AES_128_GCM_SHA256
[..]
 Elliptic curves offered:     prime256v1 secp384r1 secp521r1 X25519 
[..]
 Testing 370 ciphers via OpenSSL plus sockets against the server, ordered by encryption strength 

Hexcode  Cipher Suite Name (OpenSSL)       KeyExch.   Encryption  Bits     Cipher Suite Name (IANA/RFC)
-----------------------------------------------------------------------------------------------------------------------------
 x1302   TLS_AES_256_GCM_SHA384            ECDH 253   AESGCM      256      TLS_AES_256_GCM_SHA384                             
 x1303   TLS_CHACHA20_POLY1305_SHA256      ECDH 253   ChaCha20    256      TLS_CHACHA20_POLY1305_SHA256                       
 xc02c   ECDHE-ECDSA-AES256-GCM-SHA384     ECDH 521   AESGCM      256      TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384            
 xc024   ECDHE-ECDSA-AES256-SHA384         ECDH 521   AES         256      TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384            
 xcca9   ECDHE-ECDSA-CHACHA20-POLY1305     ECDH 253   ChaCha20    256      TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256      
 x1301   TLS_AES_128_GCM_SHA256            ECDH 253   AESGCM      128      TLS_AES_128_GCM_SHA256                             
 xc02b   ECDHE-ECDSA-AES128-GCM-SHA256     ECDH 521   AESGCM      128      TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256            
 xc023   ECDHE-ECDSA-AES128-SHA256         ECDH 521   AES         128      TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256            

Rationale

By default we:

• Require protocol TLSv1.2 or higher
• Only allows ciphers with Forward Secrecy
• Use secure and randomly chosen ECDH curves

These minimum requirements can be met by these TLS client libraries:

• OpenSSL 1.0.1 (released in 2012): for example first used in Fedora 18 (2013), Debian 7 (2013), Ubuntu 14.04 (2014)
• GnuTLS 3.2.6 (2013): for example used in Ubuntu 16.0.4 (2016)
• Android 4.4.2 (2013)

Previous less secure setting

The default settings as of UnrealIRCd 6.0.5+ work with these minimum versions of popular TLS client libraries: OpenSSL 1.0.1 (released in 2012), GnuTLS 3.2.6 (2013), Android 4.4.2 (2013).

If you need to permit clients that use an TLS library that is more than 10+ years old, then you have to downgrade the security a bit and revert to these old settings:

set {
    tls {
        protocols "All"; /* TLSv1.0 or later */
        ciphers "EECDH+CHACHA20 EECDH+AESGCM EECDH+AES AES256-GCM-SHA384 AES128-GCM-SHA256 AES256-SHA256 AES128-SHA256 AES256-SHA AES128-SHA";
    };
};

History

See also: Moving users to TLS

• Prior to UnrealIRCd 4.0.7 (2016-10-09) if you did not have a cipher setting it was left up to your OS/Distro (and ultimately OpenSSL/LibreSSL build parameters) as to which algorithms were enabled. In practice this could easily mean that ciphers such as RC4 and 3DES were enabled which is discouraged.
• In UnrealIRCd 4.0.14 (2017-09-15) the cipher list was updated to include TLSv1.3 ciphers. This means as soon as you upgrade your OpenSSL to a version which supports TLSv1.3, UnrealIRCd will be able to use it.
• In UnrealIRCd 4.0.18 (2018-06-23) support was added of setting the ECDH(E) curves via the ecdh-curves option and a default was set. Previously this was left over to the SSL library with a fallback to P-256.
• In UnrealIRCd 4.2.0 (2018-09-30) support for cipher setting for TLSv1.3 was changed to match OpenSSL specifics.
• In UnrealIRCd 4.2.2 (2019-03-01) we reordered AES-128 and AES-256. In practice, most clients (by far) already negotiated either CHACHA20 or AES-256, but now in the remaining case (non-PFS) we prefer AES-256 as well.
• In UnrealIRCd 5.0.0 (2019-12-13) there were no changes in the chipers but we did change the default generated certificate from RSA-4096 to secp384r1. On a side note, we do not recommend using a self-signed certificate. Instead, you should use a real certificate like from Let's Encrypt.
• In UnrealIRCd 6.0.5 (2022-12-29) the requirements changed to TLSv1.2 or later and a cipher with Forward Secrecy (ECDHE). This was previously in a section called A more secure setting but is now the default. The old default is now documented under Previous less secure setting.
• Doc update: curve x25519 is actually added as well since Apr 2018, if OpenSSL supports is (1.1.0+), just was not documented here.