example: sign and encrypt file

* Example to sign and encrypt a file.
* Similar to encrypt-file.py except all keys are considered trusted
  and signs with the default key.
* Also encrypts to the default key.

lang/python/examples/howto/encrypt-sign-file.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+from __future__ import absolute_import, division, unicode_literals
+
+# Copyright (C) 2018 Ben McGinnes <ben@gnupg.org>
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation; either version 2 of the License, or (at your option) any later
+# version.
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the Free
+# Software Foundation; either version 2.1 of the License, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU General Public License and the GNU
+# Lesser General Public Licensefor more details.
+#
+# You should have received a copy of the GNU General Public License and the GNU
+# Lesser General Public along with this program; if not, see
+# <http://www.gnu.org/licenses/>.
+
+import gpg
+import sys
+
+"""
+Signs and encrypts a file to a specified key.  If entering both the key and the
+filename on the command line, the key must be entered first.
+
+Signs with and also encrypts to the default key of the user invoking the
+script.  Will treat all recipients as trusted to permit encryption.
+
+Will produce both an ASCII armoured and GPG binary format copy of the encrypted
+file.
+"""
+
+if len(sys.argv) > 3:
+    a_key = sys.argv[1]
+    filename = " ".join(sys.argv[2:])
+elif len(sys.argv) == 3:
+    a_key = sys.argv[1]
+    filename = sys.argv[2]
+elif len(sys.argv) == 2:
+    a_key = sys.argv[1]
+    filename = input("Enter the path and filename to encrypt: ")
+else:
+    a_key = input("Enter the fingerprint or key ID to encrypt to: ")
+    filename = input("Enter the path and filename to encrypt: ")
+
+rkey = list(c.keylist(pattern=a_key, secret=False))
+with open(filename, "rb") as f:
+    text = f.read()
+
+with gpg.Context(armor=True) as ca:
+    ciphertext, result, sign_result = ca.encrypt(text, recipients=rkey,
+                                                 always_trust=True,
+                                                     add_encrypt_to=True)
+    with open("{0}.asc".format(filename), "wb") as fa:
+        fa.write(ciphertext)
+
+with gpg.Context() as cg:
+    ciphertext, result, sign_result = cg.encrypt(text, recipients=rkey,
+                                                 always_trust=True,
+                                                     add_encrypt_to=True)
+    with open("{0}.gpg".format(filename), "wb") as fg:
+        fg.write(ciphertext)