DICOM PS3.17 2016a - Explanatory Information

W Digital Signatures in Structured Reports Use Cases (Informative)
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# W Digital Signatures in Structured Reports Use Cases (Informative)

The scenarios in which Digital Signatures would be used in DICOM Structured Reports include, but are not limited to the following.

Case 1: Human Signed Report and Automatically Signed Evidence.

1. The archive, after receiving an MPPS complete and determining that it has the complete set of objects created during an acquisition procedure step, creates a signed Key Object Selection Document Instance with secure references to all of the DICOM composite objects that constitute the exam. The Document would include a Digital Signature according to the Basic SR Digital Signatures Secure Use Profile with the Digital Signature Purpose Code Sequence (0400,0401) of (14,ASTM-sigpurpose, "Source Signature"). It would set the Key Object Selection Document Title of that Instance to (113035, DCM, "Signed Complete Acquisition Content"). Note that the objects that are referenced in the MPPS may or may not have Digital Signatures. By creating the Key Object Selection Document Instance, the archive can in effect add the equivalent of Digital Signatures to the set of objects.

2. A post-processing system generates additional evidence objects, such as measurements or CAD reports, referring to objects in the exam. This post-processing system may or may not include Digital Signatures in the evidence objects, and may or may not be included as secure references in a signed Key Object Selection Document.

3. Working at a reporting station, a report author gathers evidences from a variety of sources, including those referenced by the Key Object Selection Document Instance and the additional evidence objects generated by the post-processing system, and incorporates his or her own observations and conclusions into one or more reports.

4. It is desired that all evidence references from a DICOM SR be secure. The application creating the SR may either:

   1. create secure references by copying a verified Digital Signature from the referenced object or by generating a MAC code directly from the referenced object,.

   2. make a secure reference to a signed Key Object Selection Document that in turn securely references the SOP Instances, or.

   3. copy the secure reference information from a trusted Key Object Selection Document to avoid the overhead of recalculating the MAC codes or revalidating the reference Digital Signatures.

5. When the author completes a DICOM SR, the system, using the author's X.509 Digital Signature Certificate generates a Digital Signature with the Digital Signature Purpose Code Sequence (0400,0401) of (1, ASTM-sigpurpose, "Author Signature") for the report.

6. The author's supervisor reviews the DICOM SR. If the supervisor approves of the report, the system sets the Verification Flag to "VERIFIED" and adds a Digital Signature with the Digital Signature Purpose Code Sequence (0400,0401) of (5, ASTM-sigpurpose, "Verification Signature") or (6, ASTM-sigpurpose, "Validation Signature") using the supervisor's X.509 certificate.

7. At some later time, someone who is reading the DICOM SR SOP Instance wishes to verify its authenticity. The system would verify that the Author Signature, as well as any Verification or Validation Signature present are intact (i.e., that the signed data has not been altered based on the recorded Digital Signatures, and that the X.509 Certificates were valid at the time that the report was created).

8. If the report reader wishes to inspect DICOM source materials referenced in a DICOM SR, the system can insure that the materials have not been altered since the report was written by verifying the Referenced Digital Signatures or the Referenced SOP Instance MAC that the report creator generated from the referenced materials.

Case 2: Cross Enterprise Document Exchange

1. An application sends by any means a set of DICOM composite objects to an entity outside of the institutional environment (e.g., for review by a third party).

2. The application creates a signed Key Object Selection Document Instance with a Key Object Selection Document Title of (113031, DCM, "Signed Manifest") referencing the set of DICOM Data Objects that it sent outside the institutional environment, and sends that SR to the external entity as a shipping manifest.

3. The external entity may utilize the Key Object Selection SR SOP Instance to confirm that it received all of the referenced objects intact (i.e., without alterations). Because the signed Key Object Selection Instance must use secure references, it can verify that the objects have not been modified.

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DICOM PS3.17 2016a - Explanatory Information