Data Destruction for Optical Discs

Tom D. MilsterUniversity of Arizona Optical Sciences Center

1630 East University Blvd., Tucson AZ 85721-0094Phone: +1-520-621-8280 FAX: +1-520-621-4358

E-mail: milster@arizona.edu

Presented at the THIC Meeting at the National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder CO

80305-5602 July 18, 2006

2

Outline

I. Introduction to Optical Data Storage

II. Data DestructionMotivation and levels of destruction

Experimental results with different types of dyes

Contrast reversal in Phthalocyanine dye

III. Pulsed Data DestructionJustification for pulsed operation

Experimental results when

Destruction characterization of data in CD-R discs in response to a high power laser beam

Recent results with a pulsed high power laser system

IV. Pulsed Laser Destroyer DeviceSystem configuration and CGH focus servo

V. Conclusion

3

Writing On a Spinning Disc(Single Layer)

• Input data stream is encoded into a drive signal for the laser

• Laser pulses energy through the illumination optics

• Light beam is focused to an intense laser spot

• Spot alters medium as disc rotates

110010010111010101010 Encoder/modulator

inputdata

stream

currentdrivesignal

lasersource

illuminationoptics

storagemedium

intense lightbeam

(half angle = θ)

newlywrittendata

scanspot

θ

Numerical aperture =NA = sin θ

Introduction

4

Reading Data From a Spinning Disc(Single Layer)

• Low-power laser beam scans data pattern on spinning disc.

• Signal energy is directed with a beam splitter to detectors.

• Detectors produce a current signal, which is then decoded into user data.

laser source(low and constant

power level)

illuminationoptics

storagemedium

beamsplitter

reflectedlight

servo/data optics

110010010111010101010

detectorsamplifier/decoder

outputdata

stream

currentsignal

data tobe read

low-powerlight beam

scanspot

θ

Introduction

5

Commercial Sector Technology Trends

clear side

center hole

data layer

CDsubstrate* (clear)

1.2 mm

clear side

clear side

data layer 2 (A,B)1.2 mm

1.2 mm

0.6 mm

0.6 mm

0.1 mm

data layer 1 (A,B)bonding agent

DVD, HD-DVD substrate* 1 (clear)

substrate* 2 (clear)

clear side

data layer (A,B)

substrate

protective layer (clear)Blu-Ray, also called BD (without cartridge)

* Substrate also serves as protective layer

Introduction

6

Planar Optical Data Storage Laboratory

Description and Objective

Description: Investigate important aspects of recording, reading and destroying data on planar substrates, like CD, DVD and BD.

Objective: Center of excellence for secure data destruction and data recovery on optical media.

Optical disc destruction device

ApproachClassify levels of erasure according to difficulty of recovery.

Identify and evaluate data destructiontechniques and devices.

Test media and evaluate samples as requested by industry and sponsors.

Provide consulting services to sponsors.

Update sponsors on new technology activity in the field.

Contact

Tom D. Milster, PI

milster@arizona.edu (520) 621-8280

Introduction

7

Motivation: Secure Destruction Minimizes Risk

(Sensitive data are commonly written to CD-type media.)

Method of Destruction Data Recovery

Toss in trash can Use commercial drive

Erase in commercial drive Use commercial drive + software

Break in fragments Use custom spin stand (G3000)

Chop or Knurl (pieces smaller than 5 mm)

Very difficult, must use microscope + custom software, very low probability of success.

High-power destroy Impossible

Incinerate Impossible

Data Destruction

8

Dye / Reflector Feature• Dye is bleached (decomposed) and gas bubbles are formed.

Substrate Feature• Melting of polycarbonate:

– Melted polycarbonate resin expands into the dye layer.– Deformation of groove side walls.

lacquerreflector

dye

substratebubble bleached dye

lacquerreflector

dye

substrate

lacquerreflector

dye

substrate

Recording Mechanism in CD-R Writable Media

2.0µm

AFM scan image of data marks

expanded substrate

groove-wall deformation

Data Destruction

9

• Laser beam exposure = 4.3 nJ/um2Cyanine Dye

unexposed area

exposed area

Optical Image

exposed

dye

substrate

60nm70nm

10nm

13nm

70nm160nm

dye

substrate

25nm

25nm

AFM measurement Before

exposure

After exposure

<data mark> <no data mark>

<data mark> <no data mark>Data Destruction

10

• Laser beam exposure = 2.8 nJ/um2Azo Dye

unexposed area

exposed area

Optical Image

exposed

84nm49nm

13nm

20nm

100nm61nm

20nm

20nm

AFM measurement Before

exposure

After exposure

<data mark> <no data mark>

<data mark> <no data mark>

dye

substrate

dye

substrate

bubbles

Data Destruction

11

Phthalocyanine Dye • Laser beam exposure = 2.2, 9.4 nJ/um2

EX = 2.2 nJ/um2 EX = 9.4 nJ/um2

99nm109nm

15nm

17nm

exposed

Optical Image

AFM measurement Before

exposure

After exposure

139nm200nm

36nm

58nm

<data mark> <no data mark>

<data mark> <no data mark>

dye

substrate

dye

substrate

EX = 9.4 nJ/um2

Data Destruction

12

Contrast Reversal in Phthalocyanine Dye

Hypothesis for contrast reversal on dye/substrate samples– phthalocyanine dye at the recorded data marks is not fully inert and responds to additional optical

energy, resulting in higher visual-wavelength reflectance of the dye.– verified by observing dark recorded data marks turning bright upon laser-exposure through a

microscope objective.Contrast enhancement on substrate-only samples

– due to mixing of the dye and the substrate material. – confirmed when exposure to a high-power laser beam caused sparking in substrate-only samples.

Brightness in data marks Before exposure After exposure Optical images of boundary betw. unexposed and exposed areas

Dark Bright

BrightBright

Dye/substrate sample

Substrate-only sample

dye

substrate

substrate

unexposed area

exposed area

unexposed area

Data Destruction

exposed area

13

Data Signals and Histograms (Phthalocyanine)

• The analog signal is retrieved from a phthalocyanine-dye disc with a CD player.• Data streams of 2 M bytes are captured using a 8-bit high-speed digitizer (NI PCI-5112)

• Histograms of pits are generated from the digitized signals.

Before destruction After exposure to intense light

TES: tracking error signal

FES: focus error signal

Data Destruction

TES

FES

DATA

expanded DATA

0 50 100 1500

500

1000

1500

2000

2500

3000

3500pits--C:\Erasure\DATA_for_DOE\040616_DOE5_000001.bin-->

This bar is for all bins longer than 140

0 50 100 1500

500

1000

1500

2000

2500

3000

3500pits--C:\Erasure\DATA_for_DOE\040616_unerased_000000.bin-->

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Images with 780nm LED (Phthalocyanine)

White light

•Data marks are dark

•Lands are brighter than grooves.

•Once exposed, data marks turn brighter than the lands.

780nm LED

•Data marks are still dark

•Lands are darker than grooves.

•Once exposed, data marks are not observable.

Exposed area

Unexposed area

* No visible, IR filters used

Exposed area

Unexposed area

< Dye/substrate > < Substrate > < Dye/substrate > < Substrate >

Data Destruction

15

Color-Filtered Images (Phthalocyanine)

No filter

Green filter

Red filter

Blue filter

< Dye/substrate sample > Kodak filters

Red

GreenBlue

Exposed area

Unexposed area

Exposed area

Both unexposed and exposed data marks are not observable in the red-filtered image due to high red light absorption in dye.

Data are still visible with the green and blue light.

Data may be retrievable from the exposedphthalocyanine discs using a modified CD readout system with a green or blue laser may retrieve.

* Exposure dose= 5.6 nJ/ µm2

** Image contrast adjusted. Data Destruction

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Observations from Destruction Experiment and a New Approach

• When a Phthalocyanine disc is exposed to a high power laser beam– Decreased data and pregroove modulation.– Data marks are visible with a microscope.– Contrast reversal on the dye/substrate samples: due to partially inert

phthalocyanine dye.– Contrast enhancement on the substrate samples: due to mixing of dye and

polycarbonate.– Once exposed to intense laser light, retrievable not with a conventional CD reader,

but with a modified CD readout system with a green or blue laser.• We expect that data destruction operation with laser pulsing at a proper

frequency will make the data on the disc irretrievable.– Need to determine the minimum track length (smallest coherent patch) required to

recover any bit of information.– Pulse the laser so that the exposed and unexposed track lengths are smaller than

the smallest coherent patch.– Then, it becomes impossible to recover any information from the disc although

data marks are visible with a microscope.

Data Destruction

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Justification for Pulsing Data Destruction

• A statistical experiment is performed to determine the minimum track length required to recover partial or complete ATIP* information using a modified commercial CD drive.

• For near-zero probability of ATIP recovery and less than 5 contiguous user bytes after descrambling, the smallest coherent patch < 5mm.

* ATIP: Absolute Time In Pregroove

The results obtained in this experiment are consistent with themicroscope data experiment.

Pulsed Data Destruction

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Pulsed Destruction Experiment

• Pulsed operation (square wave, f=10, 30, 40 kHz)• Size of the focused beam : 75um• Phthalocyanine dye

f = 10kHz f = 30kHz f = 40 kHz

18um

12um

* Image contrast adjusted

60um20um

* Image contrast adjusted

exposed area unexposed area

tracks

line beam

scan

* Image contrast adjustedPulsed Data Destruction

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Laser Destroyer using CGH Focus Sensor

s p

High power laser diode 4W, 808nm

Collimator lens

Polarizing Beam splitter

Actuator

Objective lens

Disc

Focus Servo

CGHQuad-Cell Detector

Power monitoring detector

Lens

Quarter-wave plate

kr

( ) ( )( ) ( )

FESA C B DA C B D+ − +

=+ + +

Focus Error Signal

position error

CGH Focus lensBeam

from disc

FES

-

+

A BCD

too farA B

CD

A BCD

in focus

too close

3rd order diffraction beams on Quad-cell detector

Concept of CGH Focus Servo

Diffracted beams on detector

A DCB

0th

1st

2nd3rd

-1st

-2nd

-3rd

20

Pulsed Laser Destroyer (PLD)

< Mechanical drawing of the PLD system > < Picture of the assembled PLD system >

21

Beams at Detector Plane ( ) ( )( ) ( )

FESA C B DA C B D+ − +

=+ + +

Quad-cell detector

2nd

3rdA B

CD

A B

CD

A B

CD

Out of focus In focus Out of focus

0th

1st

CGH Focus Servo

22

Video Clips of Focused Beams

3rd

2nd

1st

0th

CGH Focus Servo

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Conclusions

Three major types of recording media used in CD-Rs are characterized in response to a high power laser beam. − Data on phthalocyanine-dye discs remain optically visible after exposure to intense

laser light.− The readout signal from the exposed disc is at a noise level.− Possibly retrievable with a modified CD readout system with a green or blue laser.

By pulsed destruction operation, a disc will have alternating exposed and unexposed areas. − No modified readout system would recover any data.− No software algorithms with a microscope can be developed to recover data.

We are building a compact pulsed laser destroyer system that works for CD, DVD and BDs.

Future work− Test the feasibility of secure data destruction: DVD±R and Bluray discs.

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Publication

Conference Papers:• T. Choi and T. Milster, “Change in data marks and groove structure of CD-

recordable discs in response to a high power laser beam,” ISOM/ODS 05, Optical Society of America Topical meeting on Optical Data Storage, Proceedings of SPIE Vol. 4090, pp.329-334, Honolulu, Hawaii, July 2005.

• S. K. Kasanavesi, T. Milster, D. Felix and T. Choi, “Data Recovery from a Compact Disc Fragment,” in Optical Data Storage 2004, Proceedings of SPIE, Vol. 5380, pp. 116-127, Monterey, September 2004.

Journal papers:• T. Choi and T. Milster, “Change in Data Marks and Groove Structures of

Compact Recordable discs in Response to a High Power Laser Beam,” Optical Engineering, Vol. 45, No. 6, June 2006.

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Acknowledgements

• Warren Bletscher (technician)

• Taeyoung Choi (Ph. D student)

• David Flex (technician)

• Del Hansen (technician)

• Paul Hauser (undergraduate student)

• Sashi Kasanavesi (MS student - graduated)

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Static Measurement Method

• Static measurement instruments used to investigate the mechanisms of data mark formation and erasure.

– Optical microscope (objective lens:150X, NA=0.9)– Atomic force microscope (AFM)

• Sample preparation– Dye + Substrate sample: The lacquer and reflector layers are removed using an

air-pressure.– Substrate-only sample: The dye is washed off using alcohol after the lacquer and

reflector layers are blown off.

CD-R structure

dye

substrate

< Substrate-only sample >

substrate

< Dye + Substrate sample >

Data Destruction

27

Pulsed Laser Destroyer (PLD)