Safe to ingore: "The following packages cannot be authenticated"?

I am following the guide here  [GUIDE] Installing CrashPlan for MBL - Cloud backup

Is it safe to ingore warnings like these:

“The following packages cannot be authenticated”

I tried installing debian-archive-keyring

but end up with the following errors after apt-get -f install

The following packages have unmet dependencies:
aptitude-common: Breaks: aptitude (< 0.6.8-1) but is to be installed
debian-archive-keyring: Breaks: apt (< but is to be installed
E: Unmet dependencies. Try ‘apt-get -f install’ with no packages (or specify a solution).

Try sending a pm to the creator of the guide for more information.

Please be very cautious when performing steps like this as this might brick your drive.

This type of installations are not supported as they void the warranty on the drive.

Yhea I decided no to go with it and rely on safepoints for backups. I got the above logs from a post online.