This is correct and intended behavior I believe.
By default, packages archives shipped on the ISO images are signed with
the cdimage key, and are trusted.
This means one can perform [dist-]upgrades from installation ISOs (note
these are no longer produced by default).
And enabled one to install packages from the ISOs (e.g. install updated
openssl on a 14.04.0 host from the 14.04.1 server iso; another example
install optional drivers off the desktop iso).
You received this bug notification because you are a member of Ubuntu
Touch seeded packages, which is subscribed to ubuntu-keyring in Ubuntu.
ubuntu-keyring imports the Ubuntu CD Signing Key as a key trusted by
Status in ubuntu-keyring package in Ubuntu:
Please take this with a grain of salt as I'm not reporting it with a
clean trusty install at my fingertips.
ubuntu-keyring ships a /usr/share/keyrings/ubuntu-archive-keyring.gpg
file that contains the Ubuntu CD Signing Keys (old and new):
% gpg /usr/share/keyrings/ubuntu-archive-keyring.gpg
pub 1024D/437D05B5 2004-09-12 Ubuntu Archive Automatic Signing Key
sub 2048g/79164387 2004-09-12
pub 1024D/FBB75451 2004-12-30 Ubuntu CD Image Automatic Signing Key
pub 4096R/C0B21F32 2012-05-11 Ubuntu Archive Automatic Signing Key (2012)
pub 4096R/EFE21092 2012-05-11 Ubuntu CD Image Automatic Signing Key (2012)
They end up being trusted by apt because the keyring is taken as the
initial trusted key set in /etc/apt/trusted.gpg. This is most likely
not what we want.
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