Doesn't work; it's an age old argument ("wasn't me guv, was my mate wearing my clothes") and it will be struck from the record if you claim it with no evidence.
Remember; reasonable doubt is not just the production of an alternate theory, it requires legitimate evidence to verify.
Both the example theories you cite would usually be easy to disprove as well. The first because you could look at various aspects of activity on the computer either side of the creation of the encrypted file and show that it resembles their usual activity (for example, there are numerous other ways to do it).
Now, this is where it gets clunky. I'm speculating here, but from direct experience so... take it with caution.
If you're under investigation for something and refuse to hand over a password then you're unlikely to automatically go to jail over it. The case that probably exists is that there is evidence to support the accusation, but no actual images/material. The latter is needed for a prosecution to succeed. I've never seen a case that looks like a blank go as far as demanding encryption keys - unless you are insanely careful there will always be traces left outside the encrpted file.
(BTW, Pro Tip - if you want to be secure from investigation, scrap windows (it logs way too much) and switch to Linux. Much of the forensics stuff is Windows focused so you instantly throw the [get the right file system and the main forensic tools won't even recognise it...]. Couple that with encrypted containers and you're on to a winner)
Remember; reasonable doubt is not just the production of an alternate theory, it requires legitimate evidence to verify.
Both the example theories you cite would usually be easy to disprove as well. The first because you could look at various aspects of activity on the computer either side of the creation of the encrypted file and show that it resembles their usual activity (for example, there are numerous other ways to do it).
Now, this is where it gets clunky. I'm speculating here, but from direct experience so... take it with caution.
If you're under investigation for something and refuse to hand over a password then you're unlikely to automatically go to jail over it. The case that probably exists is that there is evidence to support the accusation, but no actual images/material. The latter is needed for a prosecution to succeed. I've never seen a case that looks like a blank go as far as demanding encryption keys - unless you are insanely careful there will always be traces left outside the encrpted file.
(BTW, Pro Tip - if you want to be secure from investigation, scrap windows (it logs way too much) and switch to Linux. Much of the forensics stuff is Windows focused so you instantly throw the [get the right file system and the main forensic tools won't even recognise it...]. Couple that with encrypted containers and you're on to a winner)