remove the dependency on gpg

I removed the dependency on GPG by making the encrypted signature file optional
rather than required.

.gitignore

@@ -1,6 +1,5 @@
 ## files from here
 *.pdf
-figures/signature.pdf
 
 ## From: https://github.com/github/gitignore/blob/master/TeX.gitignore
 ## Core latex/pdflatex auxiliary files:

Makefile

@@ -3,7 +3,9 @@
 ENC_SIGIMAGE = figures/signature.pdf.gpg
 DEC_SIGIMAGE = figures/signature.pdf
 
-all: figures/signature.pdf $(patsubst %.tex,%.pdf,$(wildcard *.tex))
+# to use encrypted signatures files, add "figures/signature.pdf" (no
+# quotes) right before the first $( in the following line:
+all: $(patsubst %.tex,%.pdf,$(wildcard *.tex))
 
 figures/signature.pdf:
 	gpg --yes --output $(DEC_SIGIMAGE) --decrypt $(ENC_SIGIMAGE)
@@ -14,7 +16,8 @@ figures/signature.pdf:
 clean:
 	latexmk -C *.tex
 	$(RM) -f *.tmp *.run.xml
-	$(RM) -f $(DEC_SIGIMAGE)
+	# to use encrypted signature files, uncomment the following line
+	# $(RM) -f $(DEC_SIGIMAGE)
 
 viewpdf: all
 	evince *.pdf

README

@@ -29,10 +29,16 @@ will required:
 * GNU Make: https://www.gnu.org/software/make/
 * latexmk: https://ctan.org/pkg/latexmk?lang=en
 
-The signature file (a gray image) is GPG encrypted file using a
-symmetric cipher. The passphrase is "weakpassword" (without
-quotes). You will want to customize this. For this file, you will also
-need GPG installed in the system.
+
+Encrypted signatures files
+===========================
+
+If you'd like, you can encrypt the signature file. There are several
+lines you in the Makefile you can uncomment to do this. We've included
+an optional encrypted copy of the fake signature file. To use it, the
+passphrase is "weakpassword" (without quotes). You will want to
+customize this. To use this, you will also need the GNU Privacy Guard
+(GPG) installed on your system.
 
 
 Contributing changes