Detection for Encrypted Email attachments not working as expected

Products

• Data Loss Prevention Network Prevent for Email

Issue/Introduction

Monitoring for encrypted email attachments DLP does not detect that an attachment is encrypted, thus no incident is generated. 

We have different encryption formats selected, but in doing some testing for Office 2016 (Word, Excel, PowerPoint) they aren't detected with these legacy formats.

Environment

DLP 14.6/15.x

Cause

File type is detected as Encrypted Office Open XML and not one of the three Microsoft file types:

• Encrypted Legacy Microsoft Word
• Encrypted Legacy Microsoft PowerPoint
• Encrypted Legacy Microsoft Excel

Resolution

This behavior is by design. DLP is not able to open and inspect password protected\encrypted files or attachments. When seeking to detect on encrypted or password protected Microsoft Office documents (Word, PowerPoint, Excel) use the Encrypted Office Open XML Encryption Format. Using this format provides desired results for the Message Attachment or File Type Match Detection Rule.