I wouldn't hand over disk encryption keys to Apple no matter how much I trusted them, purely because they're in a form where Apple could access them without my intervention, and they could conceivably be legally forced to hand over those keys by some government entity in the future.
Apple's argument against decrypting iOS devices hinges on the fact that they don't retain those keys, and therefore can't decrypt them for the government.
In your case you are looking for some way to heatmap certain keywords, or even the tone of a piece of content. You could go further and see the context of the content (which is presumably some form of document which can be parsed).
There are innumerable things online to do this. My first port of call is to trawl Github and find a repo on there which does this.
Just be careful of online services which are hoovering up your query and making off with your data...
I wrote about this setup on the blog:
"Why I run this blog on MaxCDN and Ghost"
http://blog.higg.im/2015/02/10/why-i-run-this-blog-on-maxcdn...
And very worth it getting a site off the apex too:
http://blog.higg.im/2014/03/10/getting-jque-re-off-the-apex/