Why I got such message,The following packages cannot be authenticated?

[Xiaoyang Gu <xiaoyang.backup@gmail.com>]

Today I upgraded my debian sid. I found than capplets has been
removed, and gnome-control-center provied the capplets. So I decided
to use dist-upgrade, after choosing Y, I got the message as mentioned
in the title. What's wrong? Can I install them? And a package named
jackd has been kept back. How to solve this problem?
Detailed messages are listed below:

Reading package lists... Done
Building dependency tree... Done
Calculating upgrade... Done
The following packages will be REMOVED:
  capplets
The following packages have been kept back:
  gftp gftp-common gftp-gtk gftp-text jackd nvidia-glx
  nvidia-kernel-common nvidia-kernel-source stardict stardict-tools xmms
The following packages will be upgraded:
  capplets-data gnome-control-center
2 upgraded, 0 newly installed, 1 to remove and 12 not upgraded.
Need to get 2337kB of archives.
After unpacking 1175kB disk space will be freed.
Do you want to continue [Y/n]? 
WARNING: The following packages cannot be authenticated!
  gnome-control-center capplets-data
Install these packages without verification [y/N]? 

Thanks a lot. 
                                                                      
        xiaoyang