When using gpg4win 2.3.0, you cannot change cipher-algo to most values that
should be accepted. Both GPA and Kleopatra offer you choices to modify
cipher-algo. In Kleopatra, this is: Settings -> Configure Kleopatra -> GnuPG
System -> GPG for S/MIME. In GPA, this is: Edit -> Backend preferences ->
Set Level to Advanced -> Tab GPG for S/MIME.
In both, the setting defaults to AES. In GPA, certain strings are rejected
when apply is hit, and the option then defaults back to whatever was
previously there. In Kleopatra, certain strings cause the error message
"Error from gpgconf while saving configuration: Operation not permitted".
According to gpg --version, the following ciphers are available:
AES is entered and accepted by default. When trying the other strings, the
following is observed.
When used on the command line, I am able to use the --cipher-algo argument
to perform RSA/TWOFISH on a file. I am not sure why the --cipher-algo cannot
be set from the GUI.