when i try

apt-get update

it gives as follows
Get:1 http://repo.kali.org kali-bleeding-edge Release.gpg [819 B]
Get:2 http://repo.kali.org kali-bleeding-edge Release [11.0 kB]
Ign http://repo.kali.org kali-bleeding-edge Release
Get:3 http://repo.kali.org kali-bleeding-edge/main i386 Packages [7,640 B]
Ign http://repo.kali.org kali-bleeding-edge/main Translation-en_US
Ign http://repo.kali.org kali-bleeding-edge/main Translation-en
Get:4 http://http.kali.org kali Release.gpg [819 B]
Get:5 http://security.kali.org kali/updates Release.gpg [819 B]
Get:6 http://http.kali.org kali Release [21.1 kB]
Err http://http.kali.org kali Release

Get:7 http://security.kali.org kali/updates Release [11.0 kB]
Err http://security.kali.org kali/updates Release

Fetched 53.2 kB in 10s (5,042 B/s)
Reading package lists... Done
W: GPG error: http://repo.kali.org kali-bleeding-edge Release: The following signatures were invalid: KEYEXPIRED 1425567400 KEYEXPIRED 1425567400 KEYEXPIRED 1425567400
W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://http.kali.org kali Release: The following signatures were invalid: KEYEXPIRED 1425567400 KEYEXPIRED 1425567400 KEYEXPIRED 1425567400

W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://security.kali.org kali/updates Release: The following signatures were invalid: KEYEXPIRED 1425567400 KEYEXPIRED 1425567400 KEYEXPIRED 1425567400

W: Failed to fetch http://http.kali.org/kali/dists/kali/Release

W: Failed to fetch http://security.kali.org/kali-security/dists/kali/updates/Release