This page <https://www.debian.org/releases/stable/errata > states:
"If you use APT, add the following line to /etc/apt/sources.list to be able
to access the latest security updates:
deb http://security.debian.org/ jessie/updates main contrib non-free
After that, run apt-get update followed by apt-get upgrade."
Adding that entry to /etc/apt/sources.list on the Raspberry Pi3 running Debian
Jessie results in an error message indicating that the public key is not found.
It also finds two libraries that require updating that are not found when the
above mentioned /etc/apt/sources.list entry is removed.
1. What do I need to do to prevent the error message?
2. As there are other security related URLs (doubtless, as
distributed/released) that are checked during apt-get update, is the
recommended additional entry advisable/useful for this platform?