apt-get 업데이트 실패

나에게 다음과 같은 오류가 발생합니다.

Get:1 http://kali-za.bitcrack.net/kali kali-rolling InRelease [30.5 kB]
Err:1 http://kali-za.bitcrack.net/kali kali-rolling InRelease
  The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository <[email protected]>
Reading package lists... Done
W: GPG error: http://kali-za.bitcrack.net/kali kali-rolling InRelease: The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository <[email protected]>
E: The repository 'http://http.kali.org/kali kali-rolling InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

내 소스 목록은 다음과 같습니다.

deb http://http.kali.org/kali kali-rolling main contrib non-free
# For source package access, uncomment the following line
# deb-src http://http.kali.org/kali kali-rolling main contrib non-free