anchor.diff:  
               mkdir -m 0755 -p /etc/ssh
   
  -            if ! test -f /etc/ssh/ssh_host_dsa_key; then
  -                ${pkgs.openssh}/bin/ssh-keygen -t dsa -b 1024 -f /etc/ssh/ssh_host_dsa_key -N ""
  +            if ! test -f /etc/ssh/ssh_host_${hktn}_key; then
  +                ${pkgs.openssh}/bin/ssh-keygen -t ${hktn} -b ${toString hktb} -f /etc/ssh/ssh_host_${hktn}_key -N ""
               fi
             '';
   
  
positive.code: 
          exec =
            ''
              ${pkgs.openssh}/sbin/sshd -h /etc/ssh/ssh_host_dsa_key \
                -f ${pkgs.writeText "sshd_config" cfg.extraConfig}
            '';
        };
  
negative.code:         '';
        };
  
        hostKeyType = mkOption {
          default = "dsa1024";
          description = "Type of host key to generate (dsa1024/rsa1024/ecdsa521)";
        };
  
        extraConfig = mkOption {
          default = "";
          description = "Verbatim contents of <filename>sshd_config</filename>.";
  