kali-rolling & & apt-get 업데이트 오류 - GPG error 솔루션

Today, I want to update my kali liinux. But I got a GPG error. Just like this:

# apt-get update
Get:1 http://mirrors.ustc.edu.cn/kali kali-rolling InRelease [30.5 kB]         
Get:2 http://mirrors.aliyun.com/kali kali-rolling InRelease [30.5 kB]          
Get:3 http://mirrors.tuna.tsinghua.edu.cn/kali kali-rolling InRelease [30.5 kB]
Err:1 http://mirrors.ustc.edu.cn/kali kali-rolling InRelease
  The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository 
Err:2 http://mirrors.aliyun.com/kali kali-rolling InRelease    
  The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository 
Err:3 http://mirrors.tuna.tsinghua.edu.cn/kali kali-rolling InRelease
  The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository 
Reading package lists... Done
W: GPG error: http://mirrors.ustc.edu.cn/kali kali-rolling InRelease: The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository 
E: The repository 'http://mirrors.ustc.edu.cn/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.
W: GPG error: http://mirrors.aliyun.com/kali kali-rolling InRelease: The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository 
E: The repository 'http://mirrors.aliyun.com/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.
W: GPG error: http://mirrors.tuna.tsinghua.edu.cn/kali kali-rolling InRelease: The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository 
E: The repository 'http://mirrors.tuna.tsinghua.edu.cn/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.

It is because that your kali linux is too old to be trusted.
So just update your key is ok.

wget -q -O - https://archive.kali.org/archive-key.asc | apt-key add

And I update my kali very well. Then modify the sourcelist file. And update !

# 
deb http://mirrors.ustc.edu.cn/kali kali-rolling main non-free contrib
deb-src http://mirrors.ustc.edu.cn/kali kali-rolling main non-free contrib
 
# 
#deb http://mirrors.aliyun.com/kali kali-rolling main non-free contrib
#deb-src http://mirrors.aliyun.com/kali kali-rolling main non-free contrib
 
# 
#deb http://mirrors.tuna.tsinghua.edu.cn/kali kali-rolling main contrib non-free
#deb-src https://mirrors.tuna.tsinghua.edu.cn/kali kali-rolling main contrib non-free
 
# 
#deb http://mirrors.zju.edu.cn/kali kali-rolling main contrib non-free
#deb-src http://mirrors.zju.edu.cn/kali kali-rolling main contrib non-free

root@Kali:/usr/xiaocan# apt-get update && apt-get upgrade && apt-get dist-upgrade

Perfect!