[Novalug] how to lock a file with a key

[Nino Pereira]

A simple question for security experts:

I'd like to scramble a file, send it by email,
and then unscamble it at the other end. I'd like
it to be scrambled with a key, which only I know,
so that I can unscramble it at the other end with
this same key.

Any earlier discussion about hashes and md5 and such
mostly went by me because I didn't expect to ever want to do
this, but now that I do I can't remember what to google for.

Any suggestions?

Thank you,

Nino