德尔福：30天试用 [英] Delphi: 30-day trial
问题描述
如何为我的申请进行为期30天的试用？我需要允许用户只使用30天的应用程序。如何计数这些天？
我将第一个和最后一个日期保存在注册表中。但如果要改变系统时间 - 不会有保护。我需要计算这30天。
你可能想出一个需要互联网连接但没有任何东西的系统用户不能篡改，我没有看到解决方案。
依赖于不可信元素的任何解决方案（保护的一个元素是用户的控制）是极其微弱的。
我想到的最简单的方法是防止用户将时钟移回来，是限制启动次数。但是，尝试限制启动次数需要持久性 - 将数据保存到磁盘，也许加密并存储激活数据文件的修改版本 -
想象一下，在应用程序启动后，即使在重复使用同一个日期的情况下，您也可以将30天内的一个计算为用完。为了避免在启动时使用超过1个激活时间，用户必须允许您的软件每次运行时重新保存其激活文件。
为了阻止这种方法，用户只需要保持明显的日期不被更改，加上它们必须阻止你将任何东西存储到磁盘中;或者可以使用监视进程或使用VMWare快照跟踪和记录更改并将其撤销。关于VMWare快照，您什么也不做。虚拟机的磁盘不受您的控制。
How can I make a 30-day trial for my application? I need to allow users to use an application only 30 days. How to count these days?
I keep the first and the last date in registry. But if to change a system time - no protection will be. I need to count these 30 days.
You could probably come up with a system that requires an internet connection, but without something that the user can't tamper with, I don't see a solution.
Any solutions that rely on an untrusted element (an element of the protection that is under the user's control) is critically weak.
The simplest way I can think of to protect against the user moving the clock back is to limit the total number of launches.
However, attempts to limit the number of launches requires persistence -- saving data to the disk, perhaps encrypting and storing a modified version of your activation data file -
Imagine that you count one of the 30 days as "used up" once the app has been launched, on a unique occasion, even when the same date is re-used. In order to avoid using up more than 1 "activation time day" when launched, the user must allow your software to re-save its activation file each time it runs.
To block that approach, the user needs only to keep the apparent date from changing, plus they must either prevent you from storing anything to disk; or they can simply track and record your changes and reverse them out, either using a monitoring process, or using VMWare snapshots. About VMWare snapshots, you can do nothing. The virtual machine's disk is not under your control.
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