Potential Chemical Attacks on Coatings and Tamper Evident Seal

Adhesives

Carol Cantlon, B.E. (Chemical Engineering)

EWA-Canada IT Security Evaluation & Test Facility

27 September 2005 Potential Chemical Attacks 2

OutlineOutline

• Chemical Security Mechanisms for FIPS 140-2 Physical Security

• Tamper Evident Seal Attacks• Comparison of Tamper Evident Seals to

Pick-Resistant Locks• Conformal Coatings and Paints• Epoxies• Conclusion• Recommendations

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Chemical MechanismsChemical Mechanisms

Multiple-Chip Embedded• At Physical Security Level 2

– Bleeding paint or conformal coatings

Multiple-Chip Standalone• Tamper Evidence at Physical Security Level 2 and

Above– Tamper evident seals

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Chemical Mechanisms ContinuedChemical Mechanisms Continued

Multiple-Chip Embedded or Multiple-Chip Standalone• Security Level 3

– Hard opaque coating or potting material

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Tamper Evident SealsTamper Evident Seals

Tamper Evident Seals are comprised of the following:

– the paper- with label and/or serial number

– the adhesive

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Adhesive BondAdhesive Bond

Paper

DiscontinuityEnclosureCover

or Door

Mechanical bond: adhesive of the tamper evident seal flows into microscopic holes of the surface and hardens

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Successful AttackSuccessful Attack

• Cause adhesive to flow to break bond without damaging paper

• Tamper evidence is provided by the paper and not the adhesive since adhesive residue can be cleaned from the enclosure and/or cover.

• Just need to remove seal from one part

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Paper DamagePaper Damage

• Breaks in the paper such as tears, scores or wording;

• Damage to the holograph;• Deformation, e.g. stretching of the paper;• Discoloration of the paper; and• Dye running – may also stain a hard plastic

enclosure

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Effective Methods - SolventsEffective Methods - Solvents

• Water– Usually not effective since most adhesives do not

dissolve in water

• Methyl Hydrate– Dissolves some glues

• Acetone– Effective for acrylic-based adhesives

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Effective Methods - HeatEffective Methods - Heat

• Hair dryer preferred over heat gun

• Heat gun’s high temperature-low humidity heat may crack the paper.

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Heat vs. SolventsHeat vs. Solvents

Heat does not need to be directly applied to the adhesive.

For solvents, difficulty in targeting adhesive since the adhesive is entirely covered by the paper.

Plastic, e.g. low density polyethylene, paper or metalicized paper may allow soaking of the seal in the solvent for an attack because not damaged by wetting.

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Successful Heat AttackSuccessful Heat Attack

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Why Did It Work?Why Did It Work?

• Metallic surface of seal and metal plate both reflected heat:

– Surface of seal preventing damage– Surface of metal plate directing heat to adhesive

• Metal plate expanded slightly to allow adhesive to flow

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Counteracting the Effect of Metal SurfacesCounteracting the Effect of Metal Surfaces

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Tamper Evident Seal FeatureTamper Evident Seal Feature

• Words formed in paper

• Path of least resistance on pulling of tamper evident seal from surface leaves behind words

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Seal Damaged from SolventSeal Damaged from Solvent

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Acid and Base AttacksAcid and Base Attacks

• Not as successful as other mentioned attacks

• Weak acids (H+) and bases (-OH) are similar to neutral water as a solvents.

• Strong acids and bases will damage paper and/or surfaces.

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Pick-Resistant LocksPick-Resistant Locks

• Superior to tamper evident seals for preventing access

• Require the use of drills, saws or picks to remove

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Locks vs. Tamper Evident SealsLocks vs. Tamper Evident Seals

• Tamper evident seals are easy to add to off-the-shelf enclosures.

• Theft of the key for the lock is equivalent to theft of replacement tamper evident seals.

• Discovery of combination for logical lock – loss of tamper evidence

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Adhesives Directly on CoversAdhesives Directly on Covers

• Used in the manufacturer of smaller devices, i.e. PCMCIA cards

• Thin line of adhesive exposed on the side

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AttacksAttacks

• Use syringe to inject solvent.

• Freezing attacks may be successful if adhesive becomes brittle and the covers can be separated.

• Covers may be reattached without showing tamper evidence by applying glue.

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CoatingsCoatings

• Conformal coatings include acrylics, epoxies, urethanes, parxylenes or silicones.

• Paints are polymer emulsions.

• Coatings are similar to adhesives in that they need to adhere to the circuit board.

• Epoxies can contain a tamper detection mesh.

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PolymersPolymers

• Polymers are long chain hydrocarbons which may or may not have other elements such as chlorine, nitrogen, or fluorine as part of each repeating unit or monomer.

• Polymers, by their nature, are resistant to decomposition.

• Strong acids or bases may breakdown the polymer, but also may damage circuitry.

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Common Cause of Polymer DecompositionCommon Cause of Polymer Decomposition

• A common cause of polymer decomposition is ultraviolet (UV) light.

• Free radicals generated by UV light cause monomer bonds to break.

• UV stabilizers are added to prevent decomposition.

• Use concentrated UV source to attack conformal coatings?

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Epoxy ResinsEpoxy Resins

• Made from the chemical reaction of two compounds:

Bisphenol A-Bis A (or bisphenol F-Bis F- and/or ‘Novolac’)

and

Epichlorohydrin

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Bisphenol A-Bis ABisphenol A-Bis A

Chemical product of one acetone unit

O

CH2 - C - CH2

with two phenol groups:

OH

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Solvent for EpoxiesSolvent for Epoxies

Acetone could make a good solvent for epoxies since it is a building block of them.

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ConclusionConclusion

• Chemical mechanisms used in physical security have similar properties.

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RecommendationsRecommendations

• Standardization of chemical testing approaches amongst all Cryptographic Module Testing Laboratories while still encouraging laboratory innovation

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Recommendations ContinuedRecommendations Continued

• Encourage the use of multiple layers of physical security mechanisms:– Tamper evident seals (provides better tamper

evidence) with locks (provides better access prevention)

– Tamper evidence for enclosure plus epoxy on internal circuitry