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gpgmymail

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+#!/usr/bin/python3
+
+# COPYRIGHT 2024 revsuine <pid1@revsuine.xyz>
+# Copyright 2019 Julian Andres Klode <jak@jak-linux.org>
+#
+# Licensed under the GNU General Public License version 3, which is available
+# at https://www.gnu.org/licenses/gpl-3.0.txt
+
+"""
+SOURCE: Based on the following:
+https://github.com/julian-klode/ansible.jak-linux.org/blob/49cd62c6fa2109678c751ae5c2a7e696dd761e8e/roles/mailserver/files/usr/local/lib/dovecot-sieve-filters/gpgmymail
+https://blog.jak-linux.org/2019/06/13/encrypted-email-storage/
+
+You may also want to reference the following resources:
+https://www.grepular.com/Automatically_Encrypting_all_Incoming_Email
+https://perot.me/encrypt-specific-incoming-emails-using-dovecot-and-sieve
+
+---
+
+Encrypt/Decrypt GPG/MIME messages.
+
+This tool can encrypt and decrypt emails using PGP/MIME. Decryption only
+works well for emails created with this tool. When encrypting, the tool
+preserves all headers in the original email in the encrypted part, and
+copies relevant headers to the output. When decrypting, any headers are
+ignored, and only the encrypted headers are restored.
+"""
+
+import argparse
+import sys
+import email.encoders
+import email.message
+import email.mime.application
+import email.mime.multipart
+import email.mime.message
+import typing
+
+# see: https://gnupg.readthedocs.io/en/latest/
+import gnupg
+
+def is_message_encrypted(message: email.message.Message) -> bool:
+    """Determines whether or not an email message is encrypted.
+
+    Currently just does it by checking the content type header:
+    https://stackoverflow.com/questions/18819126/checking-encryption-status-of-email"""
+
+    return message.get_content_type() == "multipart/encrypted"
+
+def encrypt(message: email.message.Message, recipients: typing.List[str]) -> str:
+    """Encrypt given message"""
+    
+    # some mail clients like Thunderbird don't like twice-encrypted emails,
+    # so we return the message as-is if it's already encrypted
+    if is_message_encrypted(message):
+        return message.as_string()
+    
+    encrypted_content = gnupg.GPG().encrypt(message.as_string(), recipients, armor=True)
+    if not encrypted_content:
+        raise ValueError(encrypted_content.status)
+    
+    # Build the parts
+    enc = email.mime.application.MIMEApplication(
+        _data=str(encrypted_content).encode(),
+        _subtype="octet-stream",
+        _encoder=email.encoders.encode_7or8bit
+    )
+
+    control = email.mime.application.MIMEApplication(
+        _data=b'Version: 1\n',
+        _subtype='pgp-encrypted; name="msg.asc"',
+        _encoder=email.encoders.encode_7or8bit
+    )
+    control['Content-Disposition'] = 'inline; filename="msg.asc"'
+
+    # Put the parts together
+    encmsg = email.mime.multipart.MIMEMultipart(
+        'encrypted',
+        protocol='application/pgp-encrypted'
+    )
+    encmsg.attach(control)
+    encmsg.attach(enc)
+
+    # Copy headers
+    headers_not_to_override = {key.lower() for key in encmsg.keys()}
+
+    for key, value in message.items():
+        if key.lower() not in headers_not_to_override:
+            encmsg[key] = value
+
+    return encmsg.as_string()
+
+def decrypt(message: email.message.Message) -> str:
+    """Decrypt the given message
+    Likely won't work on this server as I don't store private keys"""
+    return str(gnupg.GPG().decrypt(message.as_string()))
+
+def main() -> None:
+    """Program entry"""
+    parser = argparse.ArgumentParser(
+        description="Encrypt/decrypt mail using GPG/MIME"
+    )
+    parser.add_argument('-d', '--decrypt', action="store_true",
+                        help="Decrypt rather than encrypt")
+    parser.add_argument('recipient', nargs='*',
+                        help="Key ID or email of keys to encrypt for")
+    args = parser.parse_args()
+    msg = email.message_from_file(sys.stdin)
+
+    if args.decrypt:
+        sys.stdout.write(decrypt(msg))
+    else:
+        sys.stdout.write(encrypt(msg, args.recipient))
+
+if __name__ == '__main__':
+    main()
+