How to hide a code from myself until a specified time?

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http://superuser.com – Essentially, what I need is some way to generate and store a random string (20 characters long, say) for some period of time, such that there is no way for me to recover the string until the end of that period. I am running standard Ubuntu 12.10. Things that make this hard: I have root access. The computer might shut down and start up during the period. There needs to be no way for me to recover the string before the period ends. I'll have no internet access for the duration of the period. The reason I need to do this is that I have an addiction to internet porn. Most of the time I can co (HowTos)