E: Erro GPG: http://downloads.sourceforge.net all Release: As seguintes assinaturas eram inválidas: NODATA 1 NODATA 2

Question

A seguir está a saída para o sudo apt-get update

Get:1 http://deb.torproject.org precise Release.gpg [490 B]
Get:2 http://deb.torproject.org precise Release [3,709 B]                                                                                                 
Ign http://deb.torproject.org precise Release                                                                                                                
Get:3 http://http.kali.org kali Release.gpg [819 B]                                                                                                          
Get:4 http://security.kali.org kali/updates Release.gpg [819 B]                                                                             
Get:5 http://downloads.sourceforge.net all Release.gpg [163 B]                                                        
Get:6 http://http.kali.org kali Release [19.4 kB]                                                                               
Get:7 http://downloads.sourceforge.net all Release.gpg [17.1 kB]                                                                         
Get:8 http://security.kali.org kali/updates Release [11.0 kB]                                                                            
Get:9 http://http.kali.org kali/main Sources [7,555 kB]                                                                                                      
Get:10 http://downloads.sourceforge.net all Release [1,681 B]                                                                                                
Get:11 http://deb.torproject.org precise/main Sources [2,885 B]                                                                                     
Get:12 http://deb.torproject.org precise/main i386 Packages [3,933 B]                                                                                        
Ign http://deb.torproject.org precise/main Translation-en_US                                                                                                 
Ign http://deb.torproject.org precise/main Translation-en                                                                                                    
Get:13 http://downloads.sourceforge.net all/main i386 Packages [857 B]                                                                                       
Get:14 http://downloads.sourceforge.net all Release [17.1 kB]                                                                                                
Ign http://downloads.sourceforge.net all Release                                                                                                             
W: GPG error: http://deb.torproject.org precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 74A941BA219EC810
E: GPG error: http://downloads.sourceforge.net all Release: The following signatures were invalid: NODATA 1 NODATA 2

Sources.list:

## Regular repositories
deb http://http.kali.org/kali kali main non-free contrib
deb http://security.kali.org/kali-security kali/updates main contrib non-free
## Source repositories
deb-src http://http.kali.org/kali kali main non-free contrib
deb-src http://security.kali.org/kali-security kali/updates main contrib non-free

deb http://downloads.sourceforge.net/project/ubuntuxilla/mozilla/apt all main

deb http://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt all main

deb http://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt all main

O problema é que não consigo instalar nenhum software, incluindo okteta ou mesmo vlc.