nixpkgs/nixos/modules/security/dhparams.nix

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{ config, lib, pkgs, ... }:
with lib;
let
cfg = config.security.dhparams;
in
{
options = {
security.dhparams = {
params = mkOption {
description =
''
Diffie-Hellman parameters to generate.
The value is the size (in bits) of the DH params to generate. The
generated DH params path can be found in
<filename><replaceable>security.dhparams.path</replaceable>/<replaceable>name</replaceable>.pem</filename>.
Note: The name of the DH params is taken as being the name of the
service it serves: the params will be generated before the said
service is started.
Warning: If you are removing all dhparams from this list, you have
to leave security.dhparams.enable for at least one activation in
order to have them be cleaned up. This also means if you rollback to
a version without any dhparams the existing ones won't be cleaned
up.
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'';
type = with types; attrsOf int;
default = {};
example = { nginx = 3072; };
};
path = mkOption {
description =
''
Path to the directory in which Diffie-Hellman parameters will be
stored.
'';
type = types.str;
default = "/var/lib/dhparams";
};
enable = mkOption {
description =
''
Whether to generate new DH params and clean up old DH params.
'';
default = false;
type = types.bool;
};
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};
};
config = mkIf cfg.enable {
systemd.services = {
dhparams-init = {
description = "Cleanup old Diffie-Hellman parameters";
wantedBy = [ "multi-user.target" ]; # Clean up even when no DH params is set
serviceConfig.Type = "oneshot";
script =
# Create directory
''
if [ ! -d ${cfg.path} ]; then
mkdir -p ${cfg.path}
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fi
'' +
# Remove old dhparams
''
for file in ${cfg.path}/*; do
if [ ! -f "$file" ]; then
continue
fi
'' + concatStrings (mapAttrsToList (name: value:
''
if [ "$file" == "${cfg.path}/${name}.pem" ] && \
${pkgs.openssl}/bin/openssl dhparam -in "$file" -text | head -n 1 | grep "(${toString value} bit)" > /dev/null; then
continue
fi
''
) cfg.params) +
''
rm $file
done
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# TODO: Ideally this would be removing the *former* cfg.path, though this
# does not seem really important as changes to it are quite unlikely
rmdir --ignore-fail-on-non-empty ${cfg.path}
'';
};
} //
mapAttrs' (name: value: nameValuePair "dhparams-gen-${name}" {
description = "Generate Diffie-Hellman parameters for ${name} if they don't exist yet";
after = [ "dhparams-init.service" ];
before = [ "${name}.service" ];
wantedBy = [ "multi-user.target" ];
serviceConfig.Type = "oneshot";
script =
''
mkdir -p ${cfg.path}
if [ ! -f ${cfg.path}/${name}.pem ]; then
${pkgs.openssl}/bin/openssl dhparam -out ${cfg.path}/${name}.pem ${toString value}
fi
'';
}) cfg.params;
};
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}