# Presentation: 264498

## Potential Chemical Attacks on Coatings and Tamper Evident Seal Adhesives

- Carol Cantlon, B.E. (Chemical Engineering)
- EWA-Canada IT Security Evaluation & Test Facility

## Outline

- 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

- Potential Chemical Attacks

## Chemical 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

- Potential Chemical Attacks

## Chemical Mechanisms Continued

- Multiple-Chip Embedded or Multiple-Chip Standalone
- Security Level 3
- Hard opaque coating or potting material

- Potential Chemical Attacks

## Tamper Evident Seals

- Tamper Evident Seals are comprised of the following:
- the paper- with label and/or serial number
- the adhesive

- Potential Chemical Attacks

## Adhesive Bond

- Paper

- Discontinuity

- Enclosure

- Cover or Door

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

- Potential Chemical Attacks

## Successful 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

- Potential Chemical Attacks

## Paper 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

- Potential Chemical Attacks

## Effective 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

- Potential Chemical Attacks

## Effective Methods - Heat

- Hair dryer preferred over heat gun
- Heat gun’s high temperature-low humidity heat may crack the paper.

- Potential Chemical Attacks

## Heat 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.

- Potential Chemical Attacks

## Successful Heat Attack

- Potential Chemical Attacks

## 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

- Potential Chemical Attacks

## Counteracting the Effect of Metal Surfaces

- Potential Chemical Attacks

## Tamper Evident Seal Feature

- Words formed in paper
- Path of least resistance on pulling of tamper evident seal from surface leaves behind words

- Potential Chemical Attacks

## Seal Damaged from Solvent

- Potential Chemical Attacks

## Acid 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.

- Potential Chemical Attacks

## Pick-Resistant Locks

- Superior to tamper evident seals for preventing access
- Require the use of drills, saws or picks to remove

- Potential Chemical Attacks

## Locks 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

- Potential Chemical Attacks

## Adhesives Directly on Covers

- Used in the manufacturer of smaller devices, i.e. PCMCIA cards
- Thin line of adhesive exposed on the side

- Potential Chemical Attacks

## Attacks

- 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.

- Potential Chemical Attacks

## Coatings

- 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.

- Potential Chemical Attacks

## Polymers

- 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.

- Potential Chemical Attacks

## Common 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?

- Potential Chemical Attacks

## Epoxy Resins

- Made from the chemical reaction of two compounds:Bisphenol A-Bis A (or bisphenol F-Bis F- and/or ‘Novolac’)andEpichlorohydrin

- Potential Chemical Attacks

## Bisphenol A-Bis A

- 		Chemical product of one acetone unit
-                            O
-                         CH2 - C - CH2
- 		with two phenol groups:

- OH

- Potential Chemical Attacks

## Solvent for Epoxies

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

- Potential Chemical Attacks

## Conclusion

- Chemical mechanisms used in physical security have similar properties.

- Potential Chemical Attacks

## Recommendations

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

- Potential Chemical Attacks

## Recommendations 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

- Potential Chemical Attacks