确定订阅是否仍然有效而不与DateTime.Now进行比较

Question

This question may be easy and the answer obvious, but I can't seem to be able to find a solution right now. I built an application which has a big flaw in it. In a property of my User class, I check to see if the user subscription is expired. To do this, I compare the ending date of the subscription with DateTime.Now:

return (DateTime.Compare(DateTime.Now, subEndDate) > 0);

It doesn't take a genius user to realize that all it is needed is to change the Windows date to an earlier one, and then the application won't expire at all. So I think that comparing to DateTime.Now should not be done, is there a better method that I could use in order to validate a subscription date?

Thanks.

Regards,

Answer 1

调用网络服务或检查数据库以确定订阅是否仍处于活动状态

Answer 2

也许您可以从客户端程序中提取订阅到期逻辑并将其放入外部服务，然后您的客户端应用程序可以连接到其他服务器并根据传入的用户参数检索到期详细信息？

Answer 3

Does this actually matter? If your product is purely web based the only time you have to worry about is your server time. If the server time is able to be altered without your consent you probably have larger problems to worry about.

If your product is desktop based, then how much protection do you want build in? If you just want to protect against your casual user the solution you have is probably enough. If someone is determined to pirate your software then they will probably be successful. If you want to make it harder for these users one solution would be to keep a log of all the times the application has been run. This way you can get an idea of they are playing with the clock.

Answer 4

There are several NTP servers out there which you can use for free... they return the exact time and your casual user won't have a hand in manipulating those... to access them you have several options - though none built-in:

• http://dotnet-snippets.com/dns/simple-network-time-ntp-protocol-client-SID571.aspx
• http://www.codeproject.com/KB/IP/ntpclient.aspx
• http://www.codeproject.com/KB/datetime/SNTPClient.aspx
• http://www.rebex.net/time.net/ (commercial)