Andrew McIntyre Medical-Objects Digital Signatures in HL7 V2

Australian Context Require Government PKI Digital signature for paperless referral:

Digital Signature Requirements Smart Card Digital Signature Certificate embedded in signature Requests must be in plain text in EDI format Must be archivable Should remain standards compliant Should survive patient Name change Should be forwardable Should not break system unaware of signature Should be evaluable at any future time

Solution – in use for 4 years Embed Detached Signature in ED OBX segment Only sign OBX data and not delimiters Conceptually like XML digital signature Add OBX Header block with relevant OBR/PID data Patient name, Report Title, Sender but extendable Header block is also signed Advantages Allows message to be on sent in new message Allows patient demographics to change in PID Allows data to be embedded in ORF/REF messages etc Allows Classic-XML encoding transformation

Example of Signed ORU

Signature Evaluated during display

Need agreed algorithm for Hash Each OBX field in order with. as delimiter and between OBX segments The algorithm needs unique identifier Allows for HL7 version changes Can use old algorithm on new message and vice versa AUSETAV1^PKI Signature^L used in example For ORM messages can sign each order item Allows for items to be filled and removed from outstanding order list Only sign the placer fields

Advantages Digital signature is embedded and cannot be lost Message remains compliant Usual message transformations remain possible Can add copy doctors and new MSH ID Signature can be stripped off if desired Message can be archived Any PKI could be used Digital signature can be re-evaluated at any time Can transform to XML if desired