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 -

Icon  Name                    Last modified      Size  Description
[PARENTDIR] Parent Directory - [   ] InRelease 2020-07-10 07:00 2.8K [   ] Packages 2020-07-10 07:00 21K [   ] Packages.gz 2020-07-10 07:00 5.1K [TXT] Readme.txt 2008-06-03 09:27 370 [   ] Release 2020-07-10 07:00 1.9K [   ] Release.gpg 2020-07-10 07:00 833 [   ] Release.gpg.new 2017-02-15 15:28 181 [   ] Sources 2020-07-10 07:00 1.2K [   ] Sources.gz 2020-07-10 07:00 698 [DIR] aircrack-ng/ 2011-02-08 14:28 - [DIR] alsa-driver/ 2011-06-30 01:34 - [DIR] alsa-lib/ 2011-10-12 17:03 - [DIR] alsa-tools/ 2011-10-12 17:03 - [DIR] alsa-utils/ 2011-10-12 17:03 - [DIR] alsa/ 2012-09-21 09:31 - [   ] archive.key 2020-07-10 07:00 3.0K [DIR] asterisk-addons/ 2010-10-15 18:18 - [DIR] asterisk-core-sounds/ 2011-10-25 11:38 - [DIR] asterisk-extra-sounds/ 2011-06-30 01:34 - [DIR] asterisk-gui/ 2011-10-25 11:38 - [DIR] asterisk-moh-opsound/ 2010-10-15 18:30 - [DIR] asterisk/ 2012-05-24 00:46 - [DIR] atl1e/ 2009-07-08 01:44 - [DIR] atl2/ 2009-07-08 01:44 - [DIR] audiofile/ 2014-11-19 23:54 - [DIR] aufs/ 2011-09-12 17:11 - [DIR] awds/ 2010-05-27 13:16 - [DIR] batctl/ 2011-06-30 01:34 - [DIR] batman/ 2012-09-21 09:31 - [DIR] batmand/ 2012-09-21 09:31 - [DIR] bcm43xx-fwcutter/ 2006-06-01 22:24 - [TXT] build.sh 2017-03-01 15:17 654 [   ] build.sh.old 2017-02-15 16:05 642 [DIR] busybox/ 2006-11-15 23:07 - [DIR] casper/ 2006-10-07 00:42 - [DIR] crda/ 2014-11-19 23:54 - [DIR] dahdi-firmware/ 2012-05-24 00:46 - [DIR] dahdi-linux/ 2012-05-24 00:46 - [DIR] dahdi-tools/ 2012-05-24 00:46 - [DIR] dahdi/ 2014-11-19 23:54 - [DIR] et131x/ 2009-07-08 01:44 - [DIR] firmware-nonfree/ 2017-01-19 10:05 - [DIR] frottle/ 2006-06-01 22:24 - [DIR] fxload/ 2010-10-15 18:23 - [DIR] glib1.2/ 2011-06-30 01:34 - [DIR] haserl/ 2006-11-15 23:07 - [DIR] hostapd/ 2011-10-25 11:38 - [DIR] ieee80211/ 2006-06-01 22:39 - [DIR] ieee80211softmac/ 2006-06-01 22:39 - [DIR] initramfs-tools/ 2013-06-20 10:05 - [DIR] ipw2100/ 2006-06-01 22:39 - [DIR] ipw2200/ 2006-06-01 22:39 - [DIR] iw/ 2011-10-25 11:38 - [DIR] lame/ 2012-05-24 00:46 - [DIR] lcr/ 2011-02-08 14:28 - [DIR] libav/ 2017-01-19 10:05 - [DIR] libcue/ 2010-02-22 12:13 - [DIR] libffado/ 2011-10-25 11:38 - [DIR] libgea2/ 2008-06-23 01:44 - [DIR] libgea3/ 2010-05-27 13:16 - [DIR] libnl3/ 2011-10-25 11:38 - [DIR] libpri/ 2012-05-24 00:46 - [DIR] libresample/ 2010-10-15 18:26 - [DIR] libss7/ 2010-10-15 18:17 - [DIR] linux-firmware/ 2014-11-19 23:54 - [DIR] linux/ 2017-05-29 09:49 - [DIR] lirc/ 2011-09-12 17:11 - [DIR] lzma/ 2009-07-08 01:44 - [DIR] madwifi-ifupdown/ 2007-01-28 23:43 - [DIR] madwifi-ng/ 2006-11-15 23:07 - [DIR] madwifi-tools/ 2011-02-08 14:28 - [DIR] madwifi/ 2011-09-12 17:11 - [TXT] maintainers.sh 2005-03-17 10:23 108 [DIR] minidlna/ 2012-05-24 00:46 - [DIR] misdn-kernel/ 2011-02-08 14:28 - [DIR] misdn-user/ 2011-02-08 14:28 - [DIR] misdn/ 2011-10-11 01:44 - [DIR] misdnv2user/ 2011-02-08 14:28 - [DIR] mpd/ 2017-01-19 10:05 - [DIR] ncurses/ 2011-10-12 17:02 - [DIR] ndiswrapper/ 2011-09-12 17:11 - [DIR] nginx/ 2012-05-24 00:46 - [DIR] nocatauth/ 2006-06-01 22:24 - [DIR] nocatsplash/ 2011-06-30 01:34 - [DIR] olsrd/ 2010-05-27 13:16 - [DIR] openr2/ 2012-05-24 00:46 - [DIR] openssl/ 2010-02-22 12:13 - [DIR] openswan/ 2008-07-13 12:11 - [DIR] p910nd/ 2007-07-23 14:23 - [DIR] parprouted/ 2006-06-01 22:24 - [TXT] promote.sh 2009-01-08 13:05 241 [DIR] rt2400/ 2006-06-01 22:39 - [DIR] rt2500/ 2006-06-01 22:39 - [DIR] rt2860/ 2009-07-08 01:44 - [DIR] shairport/ 2015-05-04 11:40 - [DIR] snd/ 2017-05-29 09:49 - [DIR] spandsp/ 2012-05-24 00:46 - [DIR] squashfs-tools/ 2010-02-22 12:13 - [DIR] squashfs/ 2010-02-22 12:13 - [DIR] sysvinit/ 2011-10-11 14:59 - [DIR] usbmount/ 2017-03-06 11:48 - [DIR] voyage-util/ 2017-01-19 10:05 - [DIR] wavemon/ 2010-05-27 13:16 - [DIR] wifidog/ 2006-06-01 22:24 - [DIR] wireless-regdb/ 2014-10-20 11:25 - [DIR] wireless-tools/ 2008-07-13 12:11 - [DIR] wpa/ 2014-11-19 23:54 - [DIR] wpasupplicant/ 2011-10-25 11:38 - [DIR] x264/ 2012-05-24 00:46 - [DIR] xvidcore/ 2012-05-24 00:46 - [DIR] zaptel/ 2009-07-08 01:44 -
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