The minimum encryption key length in Outlook must be at least 168.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-99787	O365-OU-000011	SV-108891r2_rule		Medium

Description
This policy setting allows you to set the minimum key length for an encrypted e-mail message. If you enable this policy setting, you may set the minimum key length for an encrypted e-mail message. Outlook will display a warning dialog if the user tries to send a message using an encryption key that is below the minimum encryption key value set. The user can still choose to ignore the warning and send using the encryption key originally chosen. If you disable or do not configure this policy setting, a dialog warning will be shown to the user if the user attempts to send a message using encryption. The user can still choose to ignore the warning and send using the encryption key originally chosen.

Description

This policy setting allows you to set the minimum key length for an encrypted e-mail message. If you enable this policy setting, you may set the minimum key length for an encrypted e-mail message. Outlook will display a warning dialog if the user tries to send a message using an encryption key that is below the minimum encryption key value set. The user can still choose to ignore the warning and send using the encryption key originally chosen. If you disable or do not configure this policy setting, a dialog warning will be shown to the user if the user attempts to send a message using encryption. The user can still choose to ignore the warning and send using the encryption key originally chosen.

STIG	Date
Microsoft Office 365 ProPlus Security Technical Implementation Guide	2020-06-17

Details

Check Text ( C-98637r4_chk )
Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Cryptography >> Minimum encryption settings is set to "Enabled" and a Minimum key size (in bits) of "168" or above. Use the Windows Registry to navigate to the following key: HKCU\software\policies\microsoft\office\16.0\outlook\security If the value for minenckey is set to 168 or above, this is not a finding.

Check Text ( C-98637r4_chk )

Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Cryptography >> Minimum encryption settings is set to "Enabled" and a Minimum key size (in bits) of "168" or above.

Use the Windows Registry to navigate to the following key:

HKCU\software\policies\microsoft\office\16.0\outlook\security

If the value for minenckey is set to 168 or above, this is not a finding.

Fix Text (F-105471r3_fix)
Set the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Cryptography >> Minimum encryption settings to "Enabled"and a Minimum key size (in bits) of "168" or above.