ASD's Blueprint for Secure Cloud

Classification Labels

This section describes the design decisions associated with Microsoft 365 security features for system(s) built using ASD's Blueprint for Secure Cloud.

Estimated reading time: 4 minutes

Classification labels, located within Microsoft Purview, offers the ability to both control the data flow of sensitive information and control the retention of data. Classifications labels consists of the following:

  • Sensitivity Labels – Enable label specific protection policy settings to be enforced
  • Retention Labels – Enable label specific retention policy settings to be enforced

Sensitivity labels can be applied in the supported Microsoft applications either in Office 365 ProPlus, Microsoft Online or using the Azure Information Protection (AIP) unified labelling client.

Classification labels are published to users using Label Policies. Label Policies define the users who can utilise the label and the locations within Microsoft 365 where it can be used. Classification labels can be applied in the following ways:

  • Manually - The label is applied manually by the end-user
  • Automatically applied based on the location of the document - Labels can be configured to automatically apply based on the location of the document. For example, SharePoint
  • Automatically applied based on detected Sensitive Information Type - Labels can be configured to automatically apply based on the type of sensitive information found. For example, documents containing Australia driver’s license numbers

At the time of writing, sensitivity labels cannot be configured to satisfy all of the requirements listed in the Protective Security Policy Framework (PSPF). Some of these limitations are:

  • Sensitivity labels, Exchange Transport rules or data loss prevention (DLP), cannot set the X-Protective-Marking header *Origin- parameter prescribed in the PSPF.
  • When using DLP or Auto Labeling policies to set a X-Protective-Marking header:
    • certain characters prescribed in the PSPF are not supported (such as : and ,)
    • a character limit of 64 characters is the maximum
    • Exchange Transport rules do not have these character limitations
  • When downgrading a sensitivity label, the downgrade cannot be prevented, only forcing the user to justify the downgrade

The following Microsoft Purview Information Protection (formerly Microsoft Information Protection; MPIP) methods can be used to assist with PSPF compliance:

  • For calendar invites, advise users to add the classification to the body, and use transport rules or DLP to add the required subject and header values.
  • Update the X-Protective-Marking header associated with the MPIP label at the email gateway with the ORIGIN=user@organisation.com.au property. Note, internal emails inside the organisation wouldn’t be tagged using this method.

Example email gateway rules that work with MPIP are available in the Network Configuration ABAC document. These rules are based on regular expressions and are easily adaptable to vendor specific email gateways.

Sensitivity labels create a protective marking within the message header and when combined with Exchange mail flow rules the subject can be modified to prepend text in the subject according to the sensitivity.

Email gateway rules are available in the Network Configuration section. These rules are based on regular expressions and are easily adaptable to vendor specific email gateways.

Security & Governance

  • None identified

Design

  • None identified

References

Do you have a suggestion on how the above page could be improved? Get in touch! ASD's Blueprint for Secure Cloud is an open source project, and we would love to get your input. Submit an issue on our GitHub, or send us an email at blueprint@asd.gov.au

Acknowledgement of Country icon

Acknowledgement of Country
We acknowledge the Traditional Owners and Custodians of Country throughout Australia and their continuing connections to land, sea and communities. We pay our respects to them, their cultures and their Elders; past, present and emerging. We also recognise Australia's First Peoples' enduring contribution to Australia's national security.

Authorised by the Australian Government, Canberra