Secure apt feature has been added to 0.5 and experimental repositories.  
Although apt-get complains about the key is missing, you could still be able to 
add the packages from voyage apt repository with the key.

To add the public key to apt key rings and get rid of the error messages:

# wget http://www.voyage.hk/dists/experimental/archive.key -O - | apt-key add -

 Name                    Last modified      Size  Description
 Parent Directory                             -   
 InRelease               2026-06-11 21:00  2.8K  
 Packages                2026-06-11 21:00   21K  
 Packages.gz             2026-06-11 21:00  5.1K  
 Readme.txt              2008-06-03 09:27  370   
 Release                 2026-06-11 21:00  1.9K  
 Release.gpg             2026-06-11 21:00  833   
 Release.gpg.new         2017-02-15 15:28  181   
 Sources                 2026-06-11 21:00  1.2K  
 Sources.gz              2026-06-11 21:00  698   
 aircrack-ng/            2011-02-08 14:28    -   
 alsa-driver/            2011-06-30 01:34    -   
 alsa-lib/               2011-10-12 17:03    -   
 alsa-tools/             2011-10-12 17:03    -   
 alsa-utils/             2011-10-12 17:03    -   
 alsa/                   2012-09-21 09:31    -   
 archive.key             2026-06-11 21:00  3.0K  
 asterisk-addons/        2010-10-15 18:18    -   
 asterisk-core-sounds/   2011-10-25 11:38    -   
 asterisk-extra-sounds/  2011-06-30 01:34    -   
 asterisk-gui/           2011-10-25 11:38    -   
 asterisk-moh-opsound/   2010-10-15 18:30    -   
 asterisk/               2012-05-24 00:46    -   
 atl1e/                  2009-07-08 01:44    -   
 atl2/                   2009-07-08 01:44    -   
 audiofile/              2014-11-19 23:54    -   
 aufs/                   2011-09-12 17:11    -   
 awds/                   2010-05-27 13:16    -   
 batctl/                 2011-06-30 01:34    -   
 batman/                 2012-09-21 09:31    -   
 batmand/                2012-09-21 09:31    -   
 bcm43xx-fwcutter/       2006-06-01 22:24    -   
 build.sh                2017-03-01 15:17  654   
 build.sh.old            2017-02-15 16:05  642   
 busybox/                2006-11-15 23:07    -   
 casper/                 2006-10-07 00:42    -   
 crda/                   2014-11-19 23:54    -   
 dahdi-firmware/         2012-05-24 00:46    -   
 dahdi-linux/            2012-05-24 00:46    -   
 dahdi-tools/            2012-05-24 00:46    -   
 dahdi/                  2014-11-19 23:54    -   
 et131x/                 2009-07-08 01:44    -   
 firmware-nonfree/       2017-01-19 10:05    -   
 frottle/                2006-06-01 22:24    -   
 fxload/                 2010-10-15 18:23    -   
 glib1.2/                2011-06-30 01:34    -   
 haserl/                 2006-11-15 23:07    -   
 hostapd/                2011-10-25 11:38    -   
 ieee80211/              2006-06-01 22:39    -   
 ieee80211softmac/       2006-06-01 22:39    -   
 initramfs-tools/        2013-06-20 10:05    -   
 ipw2100/                2006-06-01 22:39    -   
 ipw2200/                2006-06-01 22:39    -   
 iw/                     2011-10-25 11:38    -   
 lame/                   2012-05-24 00:46    -   
 lcr/                    2011-02-08 14:28    -   
 libav/                  2017-01-19 10:05    -   
 libcue/                 2010-02-22 12:13    -   
 libffado/               2011-10-25 11:38    -   
 libgea2/                2008-06-23 01:44    -   
 libgea3/                2010-05-27 13:16    -   
 libnl3/                 2011-10-25 11:38    -   
 libpri/                 2012-05-24 00:46    -   
 libresample/            2010-10-15 18:26    -   
 libss7/                 2010-10-15 18:17    -   
 linux-firmware/         2014-11-19 23:54    -   
 linux/                  2017-05-29 09:49    -   
 lirc/                   2011-09-12 17:11    -   
 lzma/                   2009-07-08 01:44    -   
 madwifi-ifupdown/       2007-01-28 23:43    -   
 madwifi-ng/             2006-11-15 23:07    -   
 madwifi-tools/          2011-02-08 14:28    -   
 madwifi/                2011-09-12 17:11    -   
 maintainers.sh          2005-03-17 10:23  108   
 minidlna/               2012-05-24 00:46    -   
 misdn-kernel/           2011-02-08 14:28    -   
 misdn-user/             2011-02-08 14:28    -   
 misdn/                  2011-10-11 01:44    -   
 misdnv2user/            2011-02-08 14:28    -   
 mpd/                    2017-01-19 10:05    -   
 ncurses/                2011-10-12 17:02    -   
 ndiswrapper/            2011-09-12 17:11    -   
 nginx/                  2012-05-24 00:46    -   
 nocatauth/              2006-06-01 22:24    -   
 nocatsplash/            2011-06-30 01:34    -   
 olsrd/                  2010-05-27 13:16    -   
 openr2/                 2012-05-24 00:46    -   
 openssl/                2010-02-22 12:13    -   
 openswan/               2008-07-13 12:11    -   
 p910nd/                 2007-07-23 14:23    -   
 parprouted/             2006-06-01 22:24    -   
 promote.sh              2009-01-08 13:05  241   
 rt2400/                 2006-06-01 22:39    -   
 rt2500/                 2006-06-01 22:39    -   
 rt2860/                 2009-07-08 01:44    -   
 shairport/              2015-05-04 11:40    -   
 snd/                    2017-05-29 09:49    -   
 spandsp/                2012-05-24 00:46    -   
 squashfs-tools/         2010-02-22 12:13    -   
 squashfs/               2010-02-22 12:13    -   
 sysvinit/               2011-10-11 14:59    -   
 usbmount/               2017-03-06 11:48    -   
 voyage-util/            2017-01-19 10:05    -   
 wavemon/                2010-05-27 13:16    -   
 wifidog/                2006-06-01 22:24    -   
 wireless-regdb/         2014-10-20 11:25    -   
 wireless-tools/         2008-07-13 12:11    -   
 wpa/                    2014-11-19 23:54    -   
 wpasupplicant/          2011-10-25 11:38    -   
 x264/                   2012-05-24 00:46    -   
 xvidcore/               2012-05-24 00:46    -   
 zaptel/                 2009-07-08 01:44    -