feat: detect PGP encrypted content in partition_email and partition_msg (#1205)

### Summary

Closes #1018. Enables `partition_email` and `partition_msg` to detect if
an email has PGP encrypted content. Based on the specification in [RFC
2015](https://www.ietf.org/rfc/rfc2015.txt). The test emails are based
on the example email in the spec. If PGP detected content is detected, a
warning is emitted and an empty set of lists is returned.

### Testing

```python
from unstructured.partition_email import partition_email

filename = "example-docs/eml/fake-encrypted.eml"
partition_email(filename=filename)
```

```python
from unstructured.partition_msg import partition_msg

filename = "example-docs/fake-encrypted.msg"
partition_msgl(filename=filename)
```

CHANGELOG.md

@@ -1,8 +1,11 @@
-## 0.10.6-dev2
+## 0.10.6-dev3
 
 ### Enhancements
-* Add threaded Slack conversations into Slack connector output
 
+* Enable `partition_email` and `partition_msg` to detect if an email is PGP encryped. If
+  and email is PGP encryped, the functions will return an empy list of elements and
+  emit a warning about the encrypted content.
+* Add threaded Slack conversations into Slack connector output
 * Add functionality to sort elements using `xy-cut` sorting approach in `partition_pdf` for `hi_res` and `fast` strategies
 
 ### Features

docs/source/bricks/partition.rst

@@ -265,6 +265,9 @@ workflow looks like:
     filename=filename, process_attachments=True, attachment_partitioner=partition
   )
 
+If the content of an email is PGP encrypted, ``partition_email`` will return an empty
+list of elements and emit a warning indicated the email is encrypted.
+
 For more information about the ``partition_email`` brick, you can check the `source code here <https://github.com/Unstructured-IO/unstructured/blob/a583d47b841bdd426b9058b7c34f6aa3ed8de152/unstructured/partition/email.py>`_.
 
 
@@ -457,6 +460,9 @@ workflow looks like:
     filename=filename, process_attachments=True, attachment_partitioner=partition
   )
 
+If the content of an email is PGP encrypted, ``partition_msg`` will return an empty
+list of elements and emit a warning indicated the email is encrypted.
+
 For more information about the ``partition_msg`` brick, you can check the `source code here <https://github.com/Unstructured-IO/unstructured/blob/a583d47b841bdd426b9058b7c34f6aa3ed8de152/unstructured/partition/msg.py>`_.
 
 

example-docs/eml/fake-encrypted.eml

@@ -0,0 +1,26 @@
+From: Michael Elkins <elkins@aero.org>
+To: Michael Elkins <elkins@aero.org>
+Mime-Version: 1.0
+Content-Type: multipart/encrypted; boundary=foo;
+	protocol="application/pgp-encrypted"
+
+--foo
+Content-Type: application/pgp-encrypted
+
+Version: 1
+
+--foo
+Content-Type: application/octet-stream
+
+-----BEGIN PGP MESSAGE-----
+Version: 2.6.2
+
+hIwDY32hYGCE8MkBA/wOu7d45aUxF4Q0RKJprD3v5Z9K1YcRJ2fve87lMlDlx4Oj
+eW4GDdBfLbJE7VUpp13N19GL8e/AqbyyjHH4aS0YoTk10QQ9nnRvjY8nZL3MPXSZ
+g9VGQxFeGqzykzmykU6A26MSMexR4ApeeON6xzZWfo+0yOqAq6lb46wsvldZ96YA
+AABH78hyX7YX4uT1tNCWEIIBoqqvCeIMpp7UQ2IzBrXg6GtukS8NxbukLeamqVW3
+1yt21DYOjuLzcMNe/JNsD9vDVCvOOG3OCi8=
+=zzaA
+-----END PGP MESSAGE-----
+
+--foo--

test_unstructured/partition/msg/test_msg.py

@@ -64,6 +64,7 @@ def test_partition_msg_from_filename_with_metadata_filename():
 class MockMsOxMessage:
     def __init__(self, filename):
         self.body = "Here is an email with plain text."
+        self.header_dict = {"Content-Type": "text/plain"}
 
 
 def test_partition_msg_from_filename_with_text_content(monkeypatch):
@@ -240,3 +241,14 @@ def test_partition_msg_custom_metadata_date(
     )
 
     assert elements[0].metadata.last_modified == expected_last_modification_date
+
+
+def test_partition_msg_with_pgp_encrypted_message(
+    caplog,
+    filename="example-docs/fake-encrypted.msg",
+):
+    elements = partition_msg(filename=filename)
+
+    assert elements == []
+    assert "WARNING" in caplog.text
+    assert "Encrypted email detected" in caplog.text

test_unstructured/partition/test_email.py

@@ -549,3 +549,14 @@ def test_partition_email_odd_attachment_filename(
     )
 
     assert elements[1].metadata.filename == "odd=file=name.txt"
+
+
+def test_partition_email_with_pgp_encrypted_message(
+    caplog,
+    filename="example-docs/eml/fake-encrypted.eml",
+):
+    elements = partition_email(filename=filename)
+
+    assert elements == []
+    assert "WARNING" in caplog.text
+    assert "Encrypted email detected" in caplog.text

unstructured/__version__.py

@@ -1 +1 @@
-__version__ = "0.10.6-dev2"  # pragma: no cover
+__version__ = "0.10.6-dev3"  # pragma: no cover

unstructured/partition/email.py

@@ -14,6 +14,7 @@ from unstructured.file_utils.encoding import (
     read_txt_file,
     validate_encoding,
 )
+from unstructured.logger import logger
 from unstructured.partition.common import (
     convert_to_bytes,
     exactly_one,
@@ -49,7 +50,6 @@ from unstructured.documents.email_elements import (
     Subject,
 )
 from unstructured.file_utils.filetype import FileType, add_metadata_with_filetype
-from unstructured.logger import logger
 from unstructured.nlp.patterns import EMAIL_DATETIMETZ_PATTERN_RE
 from unstructured.partition.html import partition_html
 from unstructured.partition.text import partition_text
@@ -322,6 +322,7 @@ def partition_email(
     if not encoding:
         encoding = detected_encoding
 
+    is_encrypted = False
     content_map: Dict[str, str] = {}
     for part in msg.walk():
         # NOTE(robinson) - content dispostiion is None for the content of the email itself.
@@ -329,11 +330,26 @@ def partition_email(
         if part.get_content_disposition() is not None:
             continue
         content_type = part.get_content_type()
+
+        # NOTE(robinson) - Per RFC 2015, the content type for emails with PGP encrypted
+        # content is multipart/encrypted
+        # ref: https://www.ietf.org/rfc/rfc2015.txt
+        if content_type.endswith("encrypted"):
+            is_encrypted = True
+
         content_map[content_type] = part.get_payload()
 
     content = content_map.get(content_source, "")
-    if not content:
-        elements = []
+
+    elements: List[Element] = []
+
+    if is_encrypted:
+        logger.warning(
+            "Encrypted email detected. Partition function will return an empty list.",
+        )
+
+    elif not content:
+        pass
 
     elif content_source == "text/html":
         # NOTE(robinson) - In the .eml files, the HTML content gets stored in a format that

unstructured/partition/msg.py

@@ -6,6 +6,7 @@ import msg_parser
 
 from unstructured.documents.elements import Element, ElementMetadata, process_metadata
 from unstructured.file_utils.filetype import FileType, add_metadata_with_filetype
+from unstructured.logger import logger
 from unstructured.partition.common import exactly_one
 from unstructured.partition.email import convert_to_iso_8601
 from unstructured.partition.html import partition_html
@@ -60,8 +61,21 @@ def partition_msg(
         tmp.close()
         msg_obj = msg_parser.MsOxMessage(tmp.name)
 
+    # NOTE(robinson) - Per RFC 2015, the content type for emails with PGP encrypted
+    # content is multipart/encrypted
+    # ref: https://www.ietf.org/rfc/rfc2015.txt
+    content_type = msg_obj.header_dict.get("Content-Type", "")
+    is_encrypted = "encrypted" in content_type
+
     text = msg_obj.body
-    if "<html>" in text or "</div>" in text:
+    elements: List[Element] = []
+    if is_encrypted:
+        logger.warning(
+            "Encrypted email detected. Partition function will return an empty list.",
+        )
+    elif text is None:
+        pass
+    elif "<html>" in text or "</div>" in text:
         elements = partition_html(text=text)
     else:
         elements = partition_text(