Isn't the point of a diary that nobody can read it but you? That's why they have locks on them.
If you want a diary that other people can read, that's called a blog.
More seriously, PGP is really hard. I think it has some potential for signing emails from your bank, Amazon, etc. but other than that ... it's just a pain. I'm not a crypto expert but a reasonably skilled IT professional, and even I struggle with it.