Setting file extensions to be handled by gpg encryption problem

[bar tomas]

Hi,

I'm using gpg to encrypt files and I would like that files with 'txt'
extension be treated like 'gpg' files.
I read in the doc that this can be controlled with the variable
epa-file-name-regexp
So I added the following line at the end of my .emacs file

(setq epa-file-name-regexp "\\.txt$")

But this has absolutely no effect. I mean, if I create a txt file with
emacs, when I save it I would like for emacs to ask for an encryption
paraphrase, but it does not.

I have very little knowledge of the .emacs file, so maybe the line I
added is wrong?
Many thanks for any help