Security and DICOM Lawrence Tarbox, Ph.D. Chair, DICOM Working Group 14 Siemens Corporate Research

What’s Available Now  Use of Secure Communications Channels –Data integrity during transit –Entity authentication –Confidentiality during transit via encryption –Secure Transport Connection Profiles TSL 1.0 (derived from SSL) ISCL  Secure Use Profiles –Online Electronic Storage –Base and Bit-preserving Digital Signature (storage)

What’s Available Now  Secure Media via CMS Envelopes –Data integrity checks –Confidentiality via encryption –Only targeted recipients can access –Media Storage Security Profiles  Embedded Digital Signatures –Data integrity for the life of the SOP Instance –Identifies signatories, with optional timestamps –Digital Signature Profiles Base, Creator, and Authorization RSA Profiles

Profiles in DICOM?  Main standard body provides the ‘hooks’  Profiles provide the particulars, e.g. –Standard selection –Algorithm selection –Parameter selection  Primarily refer to existing IT standards  Easy migration to new ideas  Simplifies conformance claims

What’s coming  Attribute Level Encryption (a.k.a. de-identification) –Teaching Files –Clinical Trials –???  Audit Log Collection –Spans multiple organizations, pushed by IHE  Structured Report Digital Signature Profile

De-Identification, How? –Simply remove Data Elements that contain patient identifying information? e.g., per HIPAA’s safe harbor rules BUT –Many such Data Elements are required SO –Instead of remove, replace with a bogus value

Attribute Level Encryption  Since some use cases require controlled access to the original Attribute values: –Original values can be stored in a CMS (Cryptographic Message Syntax) envelope Embedded in the Data Set Only selected recipients can open the envelope Different subsets can be held for different recipients –Full restoration of data not a goal  Attribute Confidentiality Profiles

Attributes to be encrypted Item 1 (of only 1) Modified Attributes Sequence Cryptographic Message Syntaxt envelope CMS attributes Encrypted Content Transfer Syntax Encrypted Content encryptedContent Item 1 (of n) Encrypted Content Transfer Syntax Encrypted Content Item 2 (of n) CMS envelope Encrypted Content Transfer Syntax Encrypted Content Item n (of n) CMS envelope Encrypted Attributes Sequence Attributes (unencrypted) SOP Instance Attribute Encryption Diagram

IHE year 4: collection of trusted nodes Local authentication of user (Userid, Password) Authentication of the remote node (digital certificates) Local access control Audit trail Time synchronization System A Secure network Secure domain System B Secure domain

Selection of Standards  Use TLS for Transport Layer Security –Basic TLS Secure Transport Connection Profile  Use X.509 Certificates for node identity and keys –Basic TLS Secure Transport Connection Profile  Use NTP for Time Synchronization  Use ??? For Audit Trail Collection

Audit Log Collection  Joint NEMA / JIRA / COCIR Security and Privacy Committee proposal –Governmental regulation –Push management responsibility to one location  ASTM PS 115: Provisional Standard Specification for Audit and Disclosure Logs for Use in Health Information Systems  HL7 Common Audit Message (informative)  Part of IHE Year 4 plans

Application Specific Trigger/Content Security AdminAudit Trail Mgt User Generated Events HL7 Security SIG Driven – DICOM references DICOM WG14 Security Driven – HL7 References Audit Trail Records Transfer Session and Transport : Reliable SYSLOG or ebXML ? Common DICOM/HL7 infrastructure Audit Trail Standards in Healthcare A Proposed Model

Division of Tasks  IHE generating initial proposals –Reliable Delivery for Syslog (RFC 3195) –XML schema for defined content –IHE in Technical Framework : Out for Public Comment Now  HL7 and DICOM WG 14 work on messaging standard  ASTM and SPC work on policy issues

Signatures in SR  Identified as an important use case  Reference Mechanism –To other signed SOP Instances –To unsigned SOP Instances  Resolve issues identified during demonstrations  SR-specific Profile