IPsec/OpenVPN: Use 4,096-bit RSA for host certificates as well

  We already moved away from 2048-MODP in Core Update 170. Similarly,
German Federal Office for Information Security (BSI) recommends shifting
away from RSA keys below 3,000 bits by the end of 2022 at the latest.

The only place left in IPFire 2.x where we generate such keys is for
IPsec and OpenVPN host certificates. This patch increases their key
sizes to 4,096 bits as well - CA certificates already have this length.

Existing VPN connections cannot be migrated automatically. However, only
the respective host certificate has to be regenerated - thanks to the CA
certificates' key length being sufficient, there is no need to replace
the entire VPN CA.

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
---
 html/cgi-bin/ovpnmain.cgi | 10 ++++------
 html/cgi-bin/vpnmain.cgi  |  4 ++--
 2 files changed, 6 insertions(+), 8 deletions(-)
  

Hello Peter,

This is great.

We picked 2048 to be able to generate those keys very quickly. Since that has been a long time ago and the average hardware has become a lot faster - and RDRAND is a lot more common - this is some great change!

Best,
-Michael

Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>

> On 3 Nov 2022, at 15:29, Peter Müller <peter.mueller@ipfire.org> wrote:
> 
> We already moved away from 2048-MODP in Core Update 170. Similarly,
> German Federal Office for Information Security (BSI) recommends shifting
> away from RSA keys below 3,000 bits by the end of 2022 at the latest.
> 
> The only place left in IPFire 2.x where we generate such keys is for
> IPsec and OpenVPN host certificates. This patch increases their key
> sizes to 4,096 bits as well - CA certificates already have this length.
> 
> Existing VPN connections cannot be migrated automatically. However, only
> the respective host certificate has to be regenerated - thanks to the CA
> certificates' key length being sufficient, there is no need to replace
> the entire VPN CA.
> 
> Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
> ---
> html/cgi-bin/ovpnmain.cgi | 10 ++++------
> html/cgi-bin/vpnmain.cgi  |  4 ++--
> 2 files changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/html/cgi-bin/ovpnmain.cgi b/html/cgi-bin/ovpnmain.cgi
> index 90d3710e4..f85d610d8 100644
> --- a/html/cgi-bin/ovpnmain.cgi
> +++ b/html/cgi-bin/ovpnmain.cgi
> @@ -2,7 +2,7 @@
> ###############################################################################
> #                                                                             #
> # IPFire.org - A linux based firewall                                         #
> -# Copyright (C) 2007-2014  IPFire Team  <info@ipfire.org>                     #
> +# Copyright (C) 2007-2022  IPFire Team  <info@ipfire.org>                     #
> #                                                                             #
> # This program is free software: you can redistribute it and/or modify        #
> # it under the terms of the GNU General Public License as published by        #
> @@ -18,9 +18,7 @@
> # along with this program.  If not, see <http://www.gnu.org/licenses/>.       #
> #                                                                             #
> ###############################################################################
> -###
> -# Based on IPFireCore 77
> -###
> +
> use CGI;
> use CGI qw/:standard/;
> use Imager::QRCode;
> @@ -1970,7 +1968,7 @@ END
>    }
> } else { # child
>    unless (exec ('/usr/bin/openssl', 'req', '-nodes',
> - '-newkey', 'rsa:2048',
> + '-newkey', 'rsa:4096',
> '-keyout', "${General::swroot}/ovpn/certs/serverkey.pem",
> '-out', "${General::swroot}/ovpn/certs/serverreq.pem",
> '-extensions', 'server',
> @@ -4363,7 +4361,7 @@ if ($cgiparams{'TYPE'} eq 'net') {
> }
>    } else { # child
> unless (exec ('/usr/bin/openssl', 'req', '-nodes',
> - '-newkey', 'rsa:2048',
> + '-newkey', 'rsa:4096',
> '-keyout', "${General::swroot}/ovpn/certs/$cgiparams{'NAME'}key.pem",
> '-out', "${General::swroot}/ovpn/certs/$cgiparams{'NAME'}req.pem",
> '-config',"${General::swroot}/ovpn/openssl/ovpn.cnf")) {
> diff --git a/html/cgi-bin/vpnmain.cgi b/html/cgi-bin/vpnmain.cgi
> index fc250b1f5..6c1fd4cf0 100644
> --- a/html/cgi-bin/vpnmain.cgi
> +++ b/html/cgi-bin/vpnmain.cgi
> @@ -1093,7 +1093,7 @@ END
> &General::log("ipsec", "Creating host cert...");
> if (open(STDIN, "-|")) {
> my $opt = " req -sha256 -nodes";
> - $opt .= " -newkey rsa:2048";
> + $opt .= " -newkey rsa:4096";
> $opt .= " -keyout ${General::swroot}/certs/hostkey.pem";
> $opt .= " -out ${General::swroot}/certs/hostreq.pem";
> $errormessage = &callssl ($opt);
> @@ -2139,7 +2139,7 @@ END
> 
> if (open(STDIN, "-|")) {
> my $opt = " req -nodes -rand /proc/interrupts:/proc/net/rt_cache";
> - $opt .= " -newkey rsa:2048";
> + $opt .= " -newkey rsa:4096";
> $opt .= " -keyout ${General::swroot}/certs/$cgiparams{'NAME'}key.pem";
> $opt .= " -out ${General::swroot}/certs/$cgiparams{'NAME'}req.pem";
> 
> -- 
> 2.35.3