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Special Topics in Security andPrivacy of Medical Information

Sujata Garera

This lecture Portable patient record systems Emergency access Break the glass systems

Motivation Physicians and EMTs often encounter

unconscious patients with little medicalinformation Can be a serious issue if person has a medical

condition such as epilepsy or diabetes

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On the other hand Revealing patient information can lead to

negative consequences Employers fear that they incur the cost or risk

by hiring people with chronic conditions E.g. Stephen Orr case E.g. Cirque de Soleil case

Benefits outweigh the costs Availability of such information is vital

Hypoglycemia for example is a dangerouscondition which affects diabetic patients

Knowledge that the patient has diabetes mayexpedite diagnosis of hypoglycemia

Could prevent adverse drug reactions

Varied systems Proprietary mobile phone products USB flash drives Monitoring system Our system

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Proprietary Products AllOne Mobile Health

Consumer can access health solutions throughtheir mobile phones

Emergency access history available Security relies only on a user entered PIN

Proprietary products icePHR

In Case of Emergency Portable Health Recordsystem

User can manage and edit their personalinformation

Authentication required only when the user hasto download this information from the server

No security on locally stored records

USB flash drives for PHR Personal HealthKey

Manufactured by CapMed Stored health information Offers password based security and encryption User can carry his health records on a key

chain secured from others

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USB flash drives for PHR Personal Health Key

Analysed by Wright and Sittig [2007] Enabled the encryption Manually analyzed the file and database

structure of the device

USB flash drives for PHR Microsoft Access database with Microsoft

Jet Engine Password used to lock the database not same as

user password Password used to view database stored directly

in database file at a fixed offset scrambledagainst a fixed string with a logical operator !!

USB flash drives for PHR Device stores the users password as a string

in the database and encrypts the data with acommon password fixed by manufacturer !! Instead of

encryptedData = Epasswd(PHR data)

The manufacturer used encryptedData = Econstantpwd(PHR data)

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USB flash drives for PHR Security drawbacks

Constant encryption key Known to manufacturers Encryption flawed

Functionality drawbacks Lack of full view of records in emergency No real time processing of user data

Securing medical record onsmart phones

PHR stored on acommodity smartphone

Owner can accessrecord at any time

Emergency access tofull record alsoallowed

PHRs on Smart Phones Technique

Based on secret sharing Allows for revocation of compromised or

retired credentials Demands little of users and requires few

resources of Depends on the use of biometrics

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Building blocks Secret Sharing

Biometric key generation

Building blocks - Secret Sharing Cryptographic technique for distributing

trust among a number of parties

Secret Sharing (2,4) Will any compromise be tolerated ?

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A B

C D

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8

10

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Threshold Secret Sharing Shamir, Blakely [1979] Motivation increase confidentiality and availability (k,n) threshold scheme

Threshold k Group Size n

Confidentiality >= k shares are needed to reconstruct the secret (Atleast k) < k shares provide no information about the secret

Availability The scheme can tolerate n-k compromises

n=2k-1, so majority are correct, k-1 can be compromised

Shamir’s Secret Sharing (k,n) Threshold scheme

Secret s Prime p

p should be larger than s and n Degree k-1 polynomial f(x)

s is the constant term Dealer selects random coefficients in {0 … p-

1} and creates this polynomial f(x) f(x) = s + r1x + r2x2 + … + rk-1xk-1

Shamir’s secret sharing Assume the participants have id’s x1, x2 …

xn f(x) = s + r1x + r2x2 + … + rk-1xk-1

Share is (xi, yi = f(xi))

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ReconstructLagrange InterpolationSay R is the set depicting The correct set of atleast k shareholders

!

f (x) = y j l j (x)j"R

#

!

l j (x) =x " xix j " xii#R , j#R ,i$ j

%

Example Suppose we wanted to share the secret 1

among 3 people A,B,C such that 2 out of 3can construct Degree of polynomial ?

Example A: x1 = 1, B: x2= 2, C:x3 = 3

Say the prime is 5

Dealer chooses random values in {0, … 4} Say the polynomial is f(x) = 1+x

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Example f(x) = 1+x Share of A: (x1,y1=f(x1)) = (1,2) Share of B: (2,3) Share of C: (3,4)

Example Suppose A,B pool shares

Reconstruct polynomial f(x)

Evaluate polynomial at 0

Example Reconstruction

Lagrange Interpolation f(x) = y1l1(x) + y2l2(x) = 2l1(x) + 3l2(x) l1(x) = (x-x2)/(x1-x2) = - (x-2) l2(x) = (x -x1)/ (x2-x1) = (x-1) f(x) = -2(x-2)+ 3(x-1) = x+1

!

f (x) = y j l j (x)j"R

#

!

l j (x) =x " xix j " xii#R , j#R ,i$ j

%

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Building blocks - Biometric keygeneration Biometric signals such as finger scan are

often used for identification andauthentication Universal - everyone can be identified by the

common characteristic Unique - no two persons have the same

characteristic Permanent Collectable- measurable

Biometrics Types of biometrics

Static Finger Face

Behavioral Handwriting Voice

Biometric authentication Enrollment phase

Feature extractionand creation of abiometric templatewhich will be storedin a database

Verification Extract features and

compare againststored template

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Biometric key generation Generate key stream from biometric traits

Measurements from the iris are known to have highentropy and create cryptographic keys with securityequivalent to 128 bits

A new method for generating an invariant iris private keybased on the fuzzy vault system by Lee et al. [2008]

Recent work shows how feature extraction and Reed-Solomon error correcting codes can produce biometricbased bit sequences which can yield 128 bit keys foruse with AES

Biometric based cryptographic key generation from faces byChen et al. [2007]

Error rates are high though

Biometrics in our approach Only relying on password based security

for the medical records may create issuesduring and emergency

Use of non-behavioural features such asface and finger for securing records willallow an EMT to access them in anemergency

Division of capabilities

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Scenario 1

Text

Scenario 2

Scenario 3

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This lecture Encryption characteristics of two USB

based personal health record devices Wright and Sittig

Securing medical records on smart phones Gardner et al.

We will continue with this next time