EVALUATION OF HIPAA SECURITY REQUIREMENTS ON ENCRYPTION FOR RADIOLOGY THROUGHPUT RATES
Spencer B. Gay, M.D., Andrew M. Snyder, M.S., Alfred C. Weaver, Ph.D., Matthew J. Bassignani, M.D., Samuel J. Dwyer, III, Ph.D.
University of Virginia Health System, Charlottesville, VA
BACKGROUND Table 2 Table 5 Table 7
Almost a decade after the passage of the Health Insurance Portability and Accountability Act of 1996 [1], RESOURCE ALLOCATION TABLE ESTIMATED TIMES FOR COMPLETION OF THE STEPS PER JOB THROUGHPUT OF ENCRYPTION AND DECRYPTION ON 3 GHz PENTIUM 4
HIPAA will require compliance with its Security Standards (Section 164, 68 Fed. Reg. 8333) by April 20, 2005, STEP R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 Time T1 = 15 min (900 sec) – Patient registration by hospital registration system Encryption MB/s Percent of Decryption MB/s Percent of
for all entities covered by these rules (except small health plans which have an additional year). The Fastest Fastest
Security Standards guard electronic Protected Health Information (PHI), which includes any health care or A 1 0 0 0 0 0 0 0 0 0 0 0 T1 T2 = 5 sec – Notify HIS of patient and data using HL7 Algorithm Algorithm
health payment information that identifies or could be used to identify the individual to whom it pertains and B 1 1 0 0 1 0 0 0 0 0 0 0 T2 T3 = 30 sec – Schedule exam and notify RIS
that is stored or transmitted using electronic media. DES 56-bit 8.51 100.00% DES 56-bit 7.68 100.100%
C 0 0 1 1 1 0 0 0 0 0 0 0 T3 T4 = 10 sec – Patient data to RIS and to PACS archive
3-DES 112-bit 7.23 84.90% AES 128-bit 6.96 90.61%
The structure of the security rule is based upon three standards: D 0 1 1 0 1 0 0 0 0 1 0 0 T4 T5 = 10 sec – DICOM worklist to image modality
1. Administrative safeguards (section 164.308) AES 128-bit 7.19 84.50% 3-DES 112-bit 6.56 85.42%
E 0 0 1 0 0 1 1 0 0 0 0 0 T5 T6 = 20 min (1200 sec) – Conduct patient exam
2. Physical safeguards (section 164.310)
3. Technical safeguards (section 164.312) F 0 0 0 0 0 0 1 0 0 0 0 0 T6 T7 = 3 min (180 sec) – Patient image data to gateway via DICOM 3-DES 168-bit 7.16 84.12% 3-DES 168-bit 6.45 83.88%
and two administrative standards: G 0 0 0 0 0 1 1 1 0 0 0 0 T7 T8 = 3 min (180 sec) – Relational database image data to gateway (prior exam) AES 192-bit 6.63 77.93% AES 192-bit 6.41 83.42%
1. Organizational requirements (section 164.314)
2. Policies and procedures and documentation requirements (section 164.316). H 0 0 0 0 0 1 0 1 1 0 0 0 T8 T9 = 3 min (180 sec) – Image data from gateway to PACS archiving AES 256-bit 6.24 63.36% AES 256-bit 5.95 77.40%
I 0 0 0 0 0 1 0 1 0 1 0 0 T9 T10 = 2 min (120 sec) – Image data to workstation
The HIPAA security matrix (Appendix A, 45 CFR Part 164, Subpart C, Security Standards for the Protection of RSA 512-bit 0.90 10.53% RSA 512-bit 0.11 1.38%
Electronic Protected Health Information, published Feb. 20, 2003, 68 Fed. Reg. 8334) identifies the standards, J 0 0 0 0 0 1 0 0 0 1 1 0 T10 T11 = 2 min (120 sec) – Patient report generated in reporting system
the sections, and the implementation specifications which are either required (R) or addressable (A). Under RSA 1024-bit 0.62 7.34% RSA 1024-bit 0.04 0.47%
K 0 0 0 0 0 0 0 0 0 0 0 1 T11 T12 = 30 sec – Patient report to RIS from reporting system
the technical safeguard section, encryption and decryption (section 164.312 (a)(1)) and transmission security
L 0 0 1 0 1 0 0 0 0 0 0 1 T12 T13 = 30 sec – Patient report sent from RIS to HIS
(section 164.312 (e)(1)) are both marked as ―addressable.‖
As expected, DES was fastest because it has the shortest key and is therefore the least secure. Predictably,
M 0 1 1 0 1 0 0 0 0 0 0 0 T13
the RSA public key algorithm was slowest because it was never meant to be used with large files such as
A number of security protection schemes which proclaim HIPAA compliance are currently in use. Passwords B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12 images. The significance of Table 7 is that it reveals for the first time (in a .NET environment) what
and biometric devices provide limited authentication; firewalls are often employed for intra-hospital The bottleneck(s) can also be obtained from the resource Table 6 computational price is being paid for the superior protection of the new AES-256 encryption algorithm. AES is
security; digital signatures are used to prove message integrity. Modern data encryption and decryption allocation table, and that calculation is shown in Table 6. The RESOURCE BOTTLENECKS many orders of magnitude more secure than the other techniques, and we have shown that its use entails
algorithms are powerful techniques for data security, but their impact on throughput is not yet known. This smallest value of Bi identifies the bottleneck because resource i
Table 3 shows the resources utilized in a typical patient encounter. acceptable computational costs.
study provides an estimate of the performance impact of data encryption/decryption when applied to PACS is operating at full capacity and therefore step i is the rate- B1 = 1/(T1 + T2)
throughput. Table 3 limiting procedure. B2 = 1/(T2 + T4 + T13) Applying the data flow model as shown in Figure 1, we were able to predict the radiology department’s
RESOURCES TO BE MODELED B3 = 1/(T3 + T4 + T5 + T12 + T13) expected throughput when images were and were not encrypted and decrypted upon storage and transmission
EVALUATION METHODS R1 = Hospital registration system B4 = 1/(T3) (Table 8).
THE COMPUTING ENVIRONMENT B5 = 1/(T2 + T3 + T4 + T12 + T13)
The metric selected for this study is ―throughput.‖ To determine the ―addressable‖ implementation R2 = HIS (hospital information system) Table 8
specifications of encryption on access control and transmission security, we conducted testbed experiments R3 = RIS (radiology information system) Our experiments were performed using the Microsoft .NET B6 = 1/(T5 + T7 + T8 + T9 + T10) AVERAGE TIMES FOR EACH STEP IN THE SYSTEM
to evaluate the effect of several popular methods on radiology workflow. The methods we evaluated are framework and our test scenarios were developed in C# using B7 = 1/(T5 + T6 + T7) Time Average time without Average time with Short Description
shown in Table 1. R4 = Examination schedule system
Visual Studio .NET. By using a web services approach, we B8 = 1/(T7 + T8 + T9) Encryption Encryption
R5 = HL7 communications for text data ensured that we are moving along a language-neutral, platform- B9 = 1/(T8)
Table 1 T1 900 seconds 900 seconds Patient registration
independent path. The testbed consisted of a network of 3 GHz
ENCRYPTION METHODS SELECTED FOR EVALUATION R6 = DICOM communications for image B10 = 1/(T4 + T9 + T10)
Pentium 4 computers with 1 GB RAM each, connected via 100 T2 5 seconds 5 seconds Notify HIS of patient
Method Comments data Mbps Ethernet. B11 = 1/(T10)
B12 = 1/(T11 + T12) T3 30 seconds 30 seconds Schedule exam
R7 = Image modality unit
Data Encryption Standard (DES) Twenty years of use T4 10 seconds 11 seconds Patient data to RIS and PACS
R8 = DICOM gateway
Triple DES (3-DES) Successor to DES T5 10 seconds 10 seconds Worklist to image modality
R9 = Relational database TESTING THE PERFORMANCE OF THE ENCRYPTION ALGORITHMS
Advanced Encryption Standard (AES) Newest technique approved by the National T6 1200 seconds 1200 seconds Conduct patient exam
Institute of Standards and Technology (NIST) R10 = PACS archive
Each encryption technique shown in Table 1 was tested using four file sizes. The first file size was one byte—
T7 180 seconds 240 seconds Patient image data to gateway
Rivest, Shamir, and Adleman (RSA) The most popular public key cryptosystem R11 = Workstation the smallest possible file, and thus the one that will provide a lower bound on the overhead associated with
invoking each algorithm. The second file was 1 MB, which represents a single, compressed, 2000x1500x16 T8 180 seconds 240 seconds Relational DB images to gateway
R12 = Reporting system
screen image. The third file size was 3 MB, which represents an uncompressed 4000x3000x16 image. The T9 180 seconds 240 seconds Image data from gateway to PACS
RADIOLOGY DEPARTMENT WORKFLOW MODEL
fourth file was a 500 image MRI set, each image being 256x256x16, yielding a total file size of 68 MB. Each
file size was processed using DES with its 56-bit key, 3-DES using 128- and 192-bit keys, AES using 128-, 192-, T10 120 seconds 180 seconds Image data to workstation
The use of a radiology workflow model details how the department operates and how data flows throughout Thirteen steps in a typical information flow are shown in Table 4.
and 256-bit keys, and RSA with key sizes of 512 and 1024 bits. Each experiment performed 100 encryptions T11 120 seconds 120 seconds Patient report generation
the department (Figure 1). Models are valuable performance prediction tools, because modification of an
and decryptions on a given file size using a particular technique and key size, and then averaged the results.
operational PACS would disrupt the daily work of the department. The selected workflow model is a resource Table 4 The throughput of each algorithm was calculated from the resulting data logs. Figure 2 shows the results for T12 30 seconds 30 seconds Patient report to RIS
allocation table for estimating throughput and identifying bottlenecks. The resource allocation table (Table STEPS IN WORKFLOW MODEL the three symmetric key algorithms while Table 7 shows the results for all experiments, sorted by throughput. T13 30 seconds 30 seconds Patient report from RIS to HIS
2) is constructed with columns labeled for each of the particular resources (HIS, RIS, Networks, PACS Archive, Steps
etc.). The successive rows of the table represent the successive steps of a job or process. The right-most
column of a row identifies the average time needed for the step. The matrix entries are Boolean, with a one A. Patient registration by hospital registration system CONCLUSION
signifying that the resource is used in the step and a zero signifying that it is not. The ―bottleneck‖ of a job B. Notify HIS of patient and data using HL7 ENCRYPION AND DECRYPTION AVERAGES
is identified by inspecting each column in the table and determining the average limitation of the resource USING POLYNOMIAL FITTED LINES (n=2) Our study shows that when using the Department of Radiology dataflow model (Figure 1), a resource
throughput for each resource (the reciprocal of the sum of the execution times of the resources involved). C. Schedule exam and notify RIS allocation table (Table 2) analysis, and using symmetric key encryption on all patient data and images,
3 GHz Pentium 4 throughput would be reduced 5-7%. Knowing that the impact of encryption is small, a department could
D. Patient data to RIS and to PACS archive
Exam
14 embrace it without fearing disastrous consequences. Alternatively, if encryption were applied only to the
Hospital HL7
Patients Registration
HL7
Schedule
Image
Modality
E. DICOM worklist to image modality patient data and not to the images, then the impact of encryption would be negligible. Either way, we have
System System
F. Conduct patient exam 12 demonstrated that symmetric key encryption, especially the new AES algorithm with 256-bit keys, is a highly
DICOM DICOM DES - 56 bit secure technique that achieves HIPAA’s goals with minimal disturbance to the radiology department’s
G. Patient image data to gateway using DICOM 10 throughput.
HL7 HL7 3DES - 112 bit
DICOM
H. Relational data to gateway (required prior images)
3DES - 168 bit REFERENCES:
Time (s)
Data Worklist Gateway
8
HIS HL7 RIS I. DICOM image data from gateway to PACS archive AES - 128 bit 1. Public Law 104-191, ―Health Insurance Portability and Accountability Act of 1996.‖
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HL7 Database AES - 256 bit http://aspe.hhs.gov/admnsimp/final/txfin00.htm
K. Patient report generated in reporting system 4
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