My Debian version is 7.1 with the following info:

Distributor ID: Debian
Description: Debian GNU/Linux 7.1 (wheezy)
Release: 7.1
Codename: wheezy

PROBLEM:

I get the error message below when I tried updating. Here is the error message(below). The public are also listed

W: There is no public key available for the following key IDs:
9D6D8F6BC857C906
W: There is no public key available for the following key IDs:
7638D0442B90D010
W: There is no public key available for the following key IDs:
7638D0442B90D010
NO_PUBKEY CBF8D6FD518E17E1
W: There is no public key available for the following key IDs:
9D6D8F6BC857C906
W: GPG error: http://www.deb-multimedia.org stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5C808C2B65558117
W: GPG error: http://www.deb-multimedia.org wheezy Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5C808C2B65558117

SOLUTION:

To fix the above error message, use the following commands in bold, as root, per public key. The command and output is pasted for clarity:

root@debian7:/# gpg --recv-keys 9D6D8F6BC857C906
gpg: requesting key C857C906 from hkp server keys.gnupg.net
gpg: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key C857C906: public key "Debian Security Archive Automatic Signing Key (8/jessie) < This email address is being protected from spambots. You need JavaScript enabled to view it.>" imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
root@debian7:/# gpg --export 9D6D8F6BC857C906 | apt-key add -
OK
root@debian7:/# gpg --recv-keys 7638D0442B90D010
gpg: requesting key 2B90D010 from hkp server keys.gnupg.net
gpg: key 2B90D010: public key "Debian Archive Automatic Signing Key (8/jessie) < This email address is being protected from spambots. You need JavaScript enabled to view it.>" imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
root@debian7:/# gpg --export 7638D0442B90D010 | apt-key add -
OK
root@debian7:/# gpg --recv-keys 5C808C2B65558117
gpg: requesting key 65558117 from hkp server keys.gnupg.net
gpg: key 65558117: public key "Christian Marillat < This email address is being protected from spambots. You need JavaScript enabled to view it.>" imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
root@debian7:/# gpg --export 5C808C2B65558117 | apt-key add -
OK
root@debian7:/#

thats all folks

You have no rights to post comments