Thank you all. This is exactly what I had in mind.
(who puts "[SOLVED]" on thread's titles?)
@crts: actually I am not that "bad". I did some reading. I read and skimmed most of GnuPG's man page, but I didnīt understand it very well. The "-c" option there was not clear to me. But if your "much reading" would mean many hours of reading, then, yes, I would not want it. And I usually do not blindly follow instructions.
@dv502: my man page for "openssl" (for "OpenSSL comand line tool") doesnīt say anything about the options you used, none of them. Although the program didnīt complain to execute it.
This kind of man page, or those that mention little and says to look the Texinfo manual wich many times isnīt isntalled makes it much harder for newbies to learn the commands they have on their system. ...
@alan99: but I most probably wonīt be on the same machine and account someother time. So it wouldnīt work, or it would troublesome (and carrying a private key around isnīt much of a good idea, I guess).
@jefro: nice example of what I wanted, using GnuPG. I am surprised to have not (and now again) found anything like this on GnuPG's help pages, like http://www.gnupg.org/documentation/faqs.en.html
Good bye, all.