我正在试验 VPN，所以我想安装 pptpd。
john@desktop:~$ sudo apt-get install pptpd
[sudo] password for john:
<snip>
The following extra packages will be installed:
bcrelay
The following NEW packages will be installed:
bcrelay pptpd
0 upgraded, 2 newly installed, 0 to remove and 11 not upgraded.
Need to get 90.5 kB of archives.
After this operation, 442 kB of additional disk space will be used.
Do you want to continue [Y/n]? y
一切都运行良好，直到我到达这里：
WARNING: The following packages cannot be authenticated!
bcrelay pptpd
Install these …我创建了一个包并将其上传到我的 PPA。构建完成后，我去安装它，但遇到了以下消息：
$ sudo apt-get install stackapplet
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
stackapplet
0 upgraded, 1 newly installed, 0 to remove and 31 not upgraded.
Need to get 17.7kB of archives.
After this operation, 106kB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
stackapplet
Install these packages without verification [y/N]?
为什么它会警告我未验证软件包？