执行时debian喘息的GPG错误'；sudo-apt-get-update'；

我安装了Debian wheezy。然后我想设置apt source，如下所示：

deb http://security.debian.org/ wheezy/updates main contrib 
deb-src http://security.debian.org/ wheezy/updates main contrib 

deb http://ftp.debian.org/debian/ wheezy-updates main contrib 
deb-src http://ftp.debian.org/debian/ wheezy-updates main contrib 

然后我执行命令“sudo apt get update”，得到错误消息：

Get:1 http://security.debian.org wheezy/updates Release.gpg
Get:2 http://security.debian.org wheezy/updates Release   
Ign http://security.debian.org wheezy/updates Release       
E: GPG error: http://security.debian.org wheezy/updates Release: The following signatures were invalid: NODATA 1 NODATA 2

我的apt密钥列表输出为：

/etc/apt/trusted.gpg.d//debian-archive-squeeze-automatic.gpg
------------------------------------------------------------
pub   4096R/473041FA 2010-08-27 [expires: 2018-03-05]
uid                  Debian Archive Automatic Signing Key (6.0/squeeze) <ftpmaster@debian.org>

/etc/apt/trusted.gpg.d//debian-archive-squeeze-stable.gpg
---------------------------------------------------------
pub   4096R/B98321F9 2010-08-07 [expires: 2017-08-05]
uid                  Squeeze Stable Release Key <debian-release@lists.debian.org>

/etc/apt/trusted.gpg.d//debian-archive-wheezy-automatic.gpg
-----------------------------------------------------------
pub   4096R/46925553 2012-04-27 [expires: 2020-04-25]
uid                  Debian Archive Automatic Signing Key (7.0/wheezy) <ftpmaster@debian.org>

/etc/apt/trusted.gpg.d//debian-archive-wheezy-stable.gpg
--------------------------------------------------------
pub   4096R/65FFB764 2012-05-08 [expires: 2019-05-07]
uid                  Wheezy Stable Release Key <debian-release@lists.debian.org>

/etc/apt/trusted.gpg.d//debian-archive-squeak-automatic.gpg
------------------------------------------------------------
pub 4096R/473041FA 2010-08-27[到期日：2018-03-05]
uid Debian存档自动签名密钥（6.0/squeeze）
/etc/apt/trusted.gpg.d//debian-archive-squence-stable.gpg
---------------------------------------------------------
pub 4096R/B98321F9 2010-08-07[到期日期：2017-08-05]
液压稳定释放键
/etc/apt/trusted.gpg.d//debian-archive-wheezy-automatic.gpg
-----------------------------------------------------------
pub 4096R/46925553 2012-04-27[到期日期：2020-04-25]
uid Debian存档自动签名密钥（7.0/wheezy）
/etc/apt/trusted.gpg.d//debian-archive-wheezy-stable.gpg
--------------------------------------------------------
pub 4096R/65FFB764 2012-05-08[到期日期：2019-05-07]
油气喘息稳定释放键

如何解决GPG错误