trouble with apt-get update

[fulvio97]

how could i resolve this?

sudo apt-get update
Trovato http://downloads.sourceforge.net all InRelease                         
Trovato http://security.kali.org sana/updates InRelease                        
Scaricamento di:1 http://security.kali.org sana/updates/main Sources [103 kB]  
Scaricamento di:2 http://downloads.sourceforge.net all/main amd64 Packages [895 B]
Scaricamento di:3 http://security.kali.org sana/updates/contrib Sources [20 B] 
Scaricamento di:4 http://security.kali.org sana/updates/non-free Sources [20 B]
Scaricamento di:5 http://http.packages.debian.org import InRelease [10,4 kB]   
100% [5 InRelease gpgv 10,4 kB] [In attesa degli header] [In attesa degli headeSplitting up /var/lib/apt/lists/partial/http.packages.debian.org_dists_import_InRIgn http://http.packages.debian.org import InRelease                           
E: Errore GPG: http://http.packages.debian.org import InRelease: Il file con la firma in chiaro non è valido, ottenuto "NODATA" (la rete richiede autenticazione?) /--------> in english: file with sign isn't valid, gained "NODATA" (network request authentication)

[grid]

I'd guess the repos might be down. Have you tried again since posting?

Also, it appears you are using the deprecated Kali Sana version. I suggest upgrading to Kali Rolling.