Data Destruction for Optical Discs
Tom D. Milster
University of Arizona Optical Sciences Center 1630 East University Blvd., Tucson AZ 85721-0094
Phone: +1-520-621-8280 FAX: +1-520-621-4358 E-mail: [email protected]
Presented at the THIC Meeting at the National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder CO
80305-5602 July 18, 2006
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Outline
I. Introduction to Optical Data Storage II. Data Destruction
¾ Motivation and levels of destruction
¾ Experimental results with different types of dyes
¾ Contrast reversal in Phthalocyanine dye
III. Pulsed Data Destruction
¾ Justification for pulsed operation
¾ Experimental results when
¾ Destruction characterization of data in CD-R discs in response to a high power laser beam
¾ Recent results with a pulsed high power laser system
IV. Pulsed Laser Destroyer Device
¾ System configuration and CGH focus servo
V. Conclusion
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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 input
streamdata
current drive signal
laser source
illumination optics storage
medium intense light
(half angle = θ)beam newly
written data
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)
illumination optics storage
medium
beam splitter
reflected light servo/data
optics
110010010111010101010
detectors amplifier/
decoder output
data stream
current signal
data to be read
low-power light beam
scanspot θ
Introduction
5
Commercial Sector Technology Trends
clear side center hole
data layer CD
substrate* (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
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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
Approach
Classify levels of erasure according to difficulty of recovery.
Identify and evaluate data destruction techniques 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
[email protected] (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
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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.
lacquer
reflector
dye
substrate
bubble bleached dye
lacquer
reflector
dye
substrate
lacquer
reflector
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/um2
Cyanine Dye
unexposed area
exposed area
Optical Image
exposed
dye
substrate
70nm 60nm
10nm
13nm
70nm 160nm
dye
substrate
25nm 25nm
AFM
measurement Before exposure
After exposure
<data mark> <no data mark>
<data mark> <no data mark>
Data Destruction
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• Laser beam exposure
= 2.8 nJ/um2
Azo Dye
unexposed area
exposed area
Optical Image
exposed
84nm 49nm
13nm
20nm
100nm 61nm
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
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Phthalocyanine Dye
• Laser beam exposure= 2.2, 9.4 nJ/um2
EX = 2.2 nJ/um2 EX = 9.4 nJ/um2
109nm 99nm
15nm
17nm exposed
Optical Image
AFM
measurement Before exposure
After exposure
139nm 200nm
36nm
58nm
<data mark> <no data mark>
<data mark> <no data mark>
dye
substrate dye
substrate
EX = 9.4 nJ/um2
Data Destruction
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Contrast Reversal in Phthalocyanine Dye
9 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.
9 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
Bright Bright
Dye/substrate sample
Substrate-only sample dye
substrate
substrate
unexposed area
exposed area unexposed
area
Data Destruction
exposed area
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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 50 100 150
0 500 1000 1500 2000 2500 3000 3500
pits--C:\Erasure\DATA_for_DOE\040616_DOE5_000001.bin-->
This bar is for all bins longer than 140
0 50 100 150
0 500 1000 1500 2000 2500 3000
3500 pits--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
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Color-Filtered Images (Phthalocyanine)
No filter
Green filter Red filter
Blue filter
< Dye/substrate sample > Kodak filters
Red
Green Blue
Exposed area Unexposed area Exposed area
9 Both unexposed and exposed data marks are not observable in the red-filtered image due to high red light absorption in dye.
9Data are still visible with the green and blue light.
9 Data may be retrievable from the exposed
phthalocyanine 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
¾ The results obtained in this experiment are consistent with the microscope 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
60um
20um
* Image contrast adjusted exposed area unexposed area
tracks
line beam scan
* Image contrast adjusted Pulsed 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 Quad-Cell CGH
Detector
Power monitoring detector
Lens
Quarter-wave plate kr
( ) ( )
( ) ( )
FES A C B D
A C B D
+ − +
= + + +
Focus Error Signal
position error
CGH Focus
Beam lens from disc
FES
- +
A B
D C
too far
A B
C D
A B
D C
in focus too close
3rd order diffraction beams on Quad-cell detector
Concept of CGH Focus Servo Diffracted beams
on detector
A D
C B
0th 1st 2nd 3rd
-1st -2nd -3rd
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Pulsed Laser Destroyer (PLD)
< Mechanical drawing of the PLD system > < Picture of the assembled PLD system >
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Beams at Detector Plane
FES ((A CA C) () (BB DD))+ − +
= + + +
Quad-cell detector
2nd 3rd
A B
C D
A B
C D
A B
C D
Out of focus In focus Out of focus
0th 1st
CGH Focus Servo
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Video Clips of Focused Beams
3rd
2nd
1st
0th
CGH Focus Servo
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Conclusions
9 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.
9 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.
9 We are building a compact pulsed laser destroyer system that works for CD, DVD and BDs.
9 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
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