transparently decrypting/encrypting gpg files from Gnu Emacs 25.2.1

[Rainer Thiel <r.thiel@uni-jena.de>]

I had used Emacs to decrypt and encrypt text files transparently for
several years.  Since I use Gnu Emacs 25.2.1 for Windows, I have GPG4WIN
installed.  This had worked for several years.  «Suddenly», I can
neither encrypt nor decrypt .gpg-files because Emacs (or gpg2 when
called from Emcas) cannot find the relevant public and secret keys.

I know that I am not very specific when I say that it «suddenly» does
not work anymore.  But I am not aware I have changed anything in my
configuration (though obviously in some way I am not aware of I must
have done it), and I have no idea where to look.

I only know I still can de/encrypt files using gpg2(.exe) from the
command line, the relevant directory for the executables is in the PATH
environmental variable, and the settings in the epg-customising group
are at their standard values.  Also, it still does work on my notebook
with the same settings (in fact, I regularly mirror the HOME directory
from my desktop computer to my notebook and vice versa).

Does anyone have an idea what might go wrong here or where I should
look?

Many thanks in advance

Rainer
-- 
Prof. Dr. Rainer Thiel
Institut für Altertumswissenschaften
07737 Jena, Germany (EU)
r.thiel@uni-jena.de