我遇到了问题，“apt-get update”产生了 KEYEXPIRED 1587841717 错误：
# apt-get update
...
W: GPG error: http://archive.debian.org jessie Release: The following signatures were invalid: KEYEXPIRED 1587841717
这是我的来源列表：
# cat /etc/apt/sources.list.d/sources.list
deb http://http.debian.net/debian jessie main
deb http://http.debian.net/debian jessie contrib
deb http://archive.debian.org/debian jessie main
deb http://archive.debian.org/debian jessie contrib
这里是 apt-key 发现的过期密钥（看来密钥 46925553 于 2020-04-25 过期）：
apt-key list | grep expired -A1
pub 4096R/46925553 2012-04-27 [expired: 2020-04-25]
uid Debian Archive Automatic Signing Key (7.0/wheezy) <ftpmaster@debian.org>
--
pub 4096R/65FFB764 2012-05-08 [expired: 2019-05-07]
uid Wheezy Stable Release Key <debian-release@lists.debian.org> …