Help -- GPG error

I'm getting

"W: GPG error: http://security.debian.org wheezy/updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553"

doing apt-get/aptitude update for wheezy.

I have tried several things that I have found doing Google searches but no difference.

Here is my sources list and complete messages below

Anybody have any ideas?

TNX!!

deb http://mirrors.kernel.org/debian/ wheezy main contrib non-free
deb-src http://mirrors.kernel.org/debian/ wheezy main contrib non-free

deb http://security.debian.org/ wheezy/updates main contrib non-free
deb-src http://security.debian.org/ wheezy/updates main contrib non-free

apt-get update

Fetched 273kB in 16s (16.6kB/s)
Reading package lists... Done
W: GPG error: http://security.debian.org wheezy/updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553
W: GPG error: http://mirrors.kernel.org wheezy Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 6FB2A1C265FFB764
W: You may want to run apt-get update to correct these problems