Downloading Ubuntu source code gave a security warning:
# apt-get source gedit
Reading package lists... Done
Building dependency tree
Reading state information... Done
NOTICE: 'gedit' packaging is maintained in the 'Bzr' version control system at:
https://code.launchpad.net/~ubuntu-desktop/gedit/ubuntu
Please use:
bzr branch https://code.launchpad.net/~ubuntu-desktop/gedit/ubuntu
to retrieve the latest (possibly unreleased) updates to the package.
Need to get 3,116 kB of source archives.
Get:1 http://gb.archive.ubuntu.com/ubuntu/ vivid/main gedit 3.10.4-0ubuntu10 (dsc) [2,650 B]
Get:2 http://gb.archive.ubuntu.com/ubuntu/ vivid/main gedit 3.10.4-0ubuntu10 (tar) [3,086 kB]
Get:3 http://gb.archive.ubuntu.com/ubuntu/ vivid/main gedit 3.10.4-0ubuntu10 (diff) [26.7 kB]
Fetched 3,116 kB in 5s (611 kB/s)
gpgv: Signature made Sat 04 Apr 2015 22:31:17 BST using RSA key ID 778FA6F5
gpgv: Can't check signature: public key not found
dpkg-source: warning: failed to verify signature on ./gedit_3.10.4-0ubuntu10.dsc
It downloaded the code anyway. But why did it's key fail? And does the warning mean the downloaded files can't be trusted?