WD my cloud进行apt-get时报错:GPG error: http://ftp.us.debian.org jessie Release: The following signatures were invalid: REVKEYSIG 7638D0442B90D010 Debian Archive Automatic Signing Key

我在WD my cloud进行apt-get时出现了以下错误:
W: GPG error: http://ftp.us.debian.org jessie Release: The following signatures were invalid: REVKEYSIG 7638D0442B90D010 Debian Archive Automatic Signing Key (8/jessie) ftpmaster@debian.org

尝试过的解决方案有以下,均没有解决问题:
方法一、
# apt-get clean
# cd /var/lib/apt
# mv lists lists.old
# mkdir -p lists/partial
# apt-get clean
# apt-get update

方法二、
sudo apt-key list | grep -A 1 expired
apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 2B90D010
apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys B38A8516
apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 473041FA
apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 46925553
apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys B98321F9
apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 65FFB764

我的发行版本是:
Debian GNU/Linux 7 \n \l

请大神不吝赐教啊

实际上,我在出现问题的整个过程是这样的,受限于论坛不能发超过2个链接,所以我没有描述全。这里补充一下:
我在WD my cloud进行apt-get时先是报错:
W: GPG error: http://ftp.us.debian.org jessie Release: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 7638D0442B90D010
W: GPG error: http://ftp.us.debian.org sid Release: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 648ACFD622F3D138 NO_PUBKEY 0E98404D386FA1D9

根据网上搜的方法进行以下操作:
gpg --keyserver pgp.mit.edu --recv-keys 7638D0442B90D010
gpg --armor --export 7638D0442B90D010 | apt-key add -
gpg --keyserver pgp.mit.edu --recv-keys 648ACFD622F3D138
gpg --armor --export 648ACFD622F3D138 | apt-key add -
gpg --keyserver pgp.mit.edu --recv-keys 0E98404D386FA1D9
gpg --armor --export 0E98404D386FA1D9 | apt-key add -

重新apt-get update,才出现了原文错误