Tamper resistance
Encyclopedia
Tamper resistance is resistance to tampering by either the normal users of a product, package, or system or others with physical access to it. There are many reasons for employing tamper resistance.
Tamper resistance ranges from simple features like screws with special heads, more complex devices that render themselves inoperable or encrypt all data transmissions between individual chips, or use of materials needing special tools and knowledge. Tamper-resistant devices or features are common on packages to deter package or product tampering.
In some applications, devices are only tamper-evident
rather than tamper-resistant.
, sale, and use. No single solution can be considered as "tamper proof". Often multiple levels of security
need to be addressed to reduce the risk of tampering.
Some considerations might include:
seals may be enough to deal with this. However, they cannot easily be checked remotely, and many countries have statutory warranty terms that mean manufacturers may still have to service the equipment. Tamper proof screws will stop most casual users from tampering in the first place. In the US, the Magnuson-Moss Warranty Act
prevents manufacturers from voiding warranties solely due to tampering. A warranty may be dishonored only if the tampering actually affected the part which has failed, and could have caused the failure.
s are used to store and process private or sensitive information, such as private keys or electronic money
credit. To prevent an attacker from retrieving or modifying the information, the chips are designed so that the information is not accessible through external means and can be accessed only by the embedded software, which should contain the appropriate security measures.
Examples of tamper-resistant chips include all secure cryptoprocessor
s, such as the IBM 4758
and chips used in smartcards, as well as the Clipper chip
.
It has been argued that it is very difficult to make simple electronic devices secure against tampering, because numerous attacks are possible, including:
Tamper-resistant chips may be designed to zeroise
their sensitive data (especially cryptographic keys) if they detect penetration of their security encapsulation or out-of-specification environmental parameters. A chip may even be rated for "cold zeroisation", the ability to zeroise itself even after its power supply has been crippled. Additionally, the custom-made encapsulation methods used for chips used in some cryptographic products may be designed in such a manner that they are internally pre-stressed, so the chip will fracture if interfered with.
Nevertheless, the fact that an attacker may have the device in his possession for as long as he likes, and perhaps obtain numerous other samples for testing and practice, means that it is practically impossible to totally eliminate tampering by a sufficiently motivated opponent. Because of this, one of the most important elements in protecting a system is overall system design. In particular, tamper-resistant systems should "fail gracefully" by ensuring that compromise of one device does not compromise the entire system. In this manner, the attacker can be practically restricted to attacks that cost less than the expected return from compromising a single device (plus, perhaps, a little more for kudos
). Since the most sophisticated attacks have been estimated to cost several hundred thousand dollars to carry out, carefully designed systems may be invulnerable in practice.
s, set-top box
es and other devices that use digital rights management
. In this case the issue is not about stopping the user from breaking the equipment or hurting themselves, but about either stopping them from extracting codes or acquiring and saving the decoded bitstream. This is usually done by having lots of features on each chip and making sure the busses between chips are encrypted.
DRM mechanisms also use certificates and asymmetric Key cryptography in many cases. In all such cases, tamper resistance means not allowing access to the valid device certificates/ public-private keys of the device to the device user. The process of making software robust against tampering attacks is referred to as software anti-tamper.
will feature a combination of anti-tamper techniques that will make it difficult to get at the nuclear material, ensure that where the reactors are transported to is closely tracked, and have alarms in place that sound if attempts at entry are detected (which can then be responded to by the military).
The tamper resistance of packaging can be evaluated by consultants and experts in the subject. Also, comparisons of various packages can be made by careful field testing of the lay public.
harder, or to prevent a user from modifying it against the manufacturer's wishes (removing a restriction on how it can be used, for example). One commonly used method is code obfuscation
.
However, effective tamper resistance in software is much harder than in hardware, as the software environment can be manipulated to near-arbitrary extent by the use of emulation.
If implemented, trusted computing
would make software tampering of protected programs at least as difficult as hardware tampering, as the user would have to hack the trust chip to give false certifications in order to bypass remote attestation and sealed storage. However, the current specification makes it clear that the chip is not expected to be tamper-proof against any reasonably sophisticated physical attack; that is, it is not intended to be as secure as a tamper-resistant device.
A side effect of this is that software maintenance gets more complex, because software updates need to be validated and errors in the upgrade process may lead to a false-positive triggering of the protection mechanism.
Tamper resistance ranges from simple features like screws with special heads, more complex devices that render themselves inoperable or encrypt all data transmissions between individual chips, or use of materials needing special tools and knowledge. Tamper-resistant devices or features are common on packages to deter package or product tampering.
In some applications, devices are only tamper-evident
Tamper-evident
Tamper-evident describes a device or process that makes unauthorized access to the protected object easily detected. Seals, markings or other techniques may be tamper indicating.-Tampering:...
rather than tamper-resistant.
Tampering
Tampering involves the deliberate altering or adulteration of a product, package, or system. Solutions may involve all phases of product production, packaging, distribution, logisticsLogistics
Logistics is the management of the flow of goods between the point of origin and the point of destination in order to meet the requirements of customers or corporations. Logistics involves the integration of information, transportation, inventory, warehousing, material handling, and packaging, and...
, sale, and use. No single solution can be considered as "tamper proof". Often multiple levels of security
Security
Security is the degree of protection against danger, damage, loss, and crime. Security as a form of protection are structures and processes that provide or improve security as a condition. The Institute for Security and Open Methodologies in the OSSTMM 3 defines security as "a form of protection...
need to be addressed to reduce the risk of tampering.
Some considerations might include:
- Identify who a potential tamperer might be: average user, child, psychopath, misguided joker, saboteur, organized criminals, terrorists. What level of knowledge, materials, tools, etc. might they have?
- Identify all feasible methods of unauthorized access into a product, package, or system. In addition to the primary means of entry, also consider secondary or "back door" methods.
- Control or limit access to products or systems of interest.
- Improve the tamper resistance to make tampering more difficult, time-consuming, etc.
- Add tamper-evidentTamper-evidentTamper-evident describes a device or process that makes unauthorized access to the protected object easily detected. Seals, markings or other techniques may be tamper indicating.-Tampering:...
features to help indicate the existence of tampering. - Educate people to watch for evidence of tampering.
Safety
Nearly all mains appliances and accessories can only be opened with the use of a screwdriver (or a substitute item such as a nail file or kitchen knife). This prevents children and others who are careless or unaware of the dangers of opening the equipment from doing so and hurting themselves (from electrical shocks, burns or cuts, for example) or damaging the equipment. Sometimes (especially in order to avoid litigation), manufacturers go further and use tamper-resistant screws, which cannot be unfastened with standard equipment. Tamper-resistant screws are also used on electrical fittings in many public buildings primarily to reduce tampering or vandalism that may cause a danger to others.Warranties and support
A user who breaks equipment by modifying it in a way not intended by the manufacturer might deny they did it, in order to claim the warranty or (mainly in the case of PCs) call the helpdesk for help in fixing it. Tamper-evidentTamper-evident
Tamper-evident describes a device or process that makes unauthorized access to the protected object easily detected. Seals, markings or other techniques may be tamper indicating.-Tampering:...
seals may be enough to deal with this. However, they cannot easily be checked remotely, and many countries have statutory warranty terms that mean manufacturers may still have to service the equipment. Tamper proof screws will stop most casual users from tampering in the first place. In the US, the Magnuson-Moss Warranty Act
Magnuson-Moss Warranty Act
The Magnuson–Moss Warranty Act is a United States federal law, . Enacted in 1975, it is the federal statute that governs warranties on consumer products. The Act was sponsored by Senator Warren G. Magnuson of Washington and U.S. Rep John E...
prevents manufacturers from voiding warranties solely due to tampering. A warranty may be dishonored only if the tampering actually affected the part which has failed, and could have caused the failure.
Security
Tamper-resistant microprocessorMicroprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s are used to store and process private or sensitive information, such as private keys or electronic money
Electronic money
Electronic money is money or scrip that is only exchanged electronically. Typically, this involves the use of computer networks, the internet and digital stored value systems...
credit. To prevent an attacker from retrieving or modifying the information, the chips are designed so that the information is not accessible through external means and can be accessed only by the embedded software, which should contain the appropriate security measures.
Examples of tamper-resistant chips include all secure cryptoprocessor
Secure cryptoprocessor
A secure cryptoprocessor is a dedicated computer on a chip or microprocessor for carrying out cryptographic operations, embedded in a packaging with multiple physical security measures, which give it a degree of tamper resistance....
s, such as the IBM 4758
IBM 4758
The IBM 4758 PCI Cryptographic Coprocessor is a secure cryptoprocessor implemented on a high-security, tamper resistant, programmable PCI board...
and chips used in smartcards, as well as the Clipper chip
Clipper chip
The Clipper chip was a chipset that was developed and promoted by the U.S. National Security Agency as an encryption device to be adopted by telecommunications companies for voice transmission...
.
It has been argued that it is very difficult to make simple electronic devices secure against tampering, because numerous attacks are possible, including:
- physical attack of various forms (microprobing, drills, files, solvents, etc.)
- freezing the device
- applying out-of-spec voltages or power surges
- applying unusual clock signals
- inducing software errors using radiation (e.g. microwaveMicrowaveMicrowaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
s or ionising radiation) - measuring the precise time and power requirements of certain operations (see power analysisPower analysisIn cryptography, power analysis is a form of side channel attack in which the attacker studies the power consumption of a cryptographic hardware device...
)
Tamper-resistant chips may be designed to zeroise
Zeroisation
In cryptography, zeroisation is the practice of erasing sensitive parameters from a cryptographic module to prevent their disclosure if the equipment is captured. This is generally accomplished by altering or deleting the contents to prevent recovery of the data...
their sensitive data (especially cryptographic keys) if they detect penetration of their security encapsulation or out-of-specification environmental parameters. A chip may even be rated for "cold zeroisation", the ability to zeroise itself even after its power supply has been crippled. Additionally, the custom-made encapsulation methods used for chips used in some cryptographic products may be designed in such a manner that they are internally pre-stressed, so the chip will fracture if interfered with.
Nevertheless, the fact that an attacker may have the device in his possession for as long as he likes, and perhaps obtain numerous other samples for testing and practice, means that it is practically impossible to totally eliminate tampering by a sufficiently motivated opponent. Because of this, one of the most important elements in protecting a system is overall system design. In particular, tamper-resistant systems should "fail gracefully" by ensuring that compromise of one device does not compromise the entire system. In this manner, the attacker can be practically restricted to attacks that cost less than the expected return from compromising a single device (plus, perhaps, a little more for kudos
Kudos
Kudos is an English word meaning acclaim or praise for exceptional achievement.Kudos may also refer to:* KUDOS, a vocational-counseling computer program* Kudos , a chocolate-covered cereal bar...
). Since the most sophisticated attacks have been estimated to cost several hundred thousand dollars to carry out, carefully designed systems may be invulnerable in practice.
DRM
Tamper resistance finds application in smart cardSmart card
A smart card, chip card, or integrated circuit card , is any pocket-sized card with embedded integrated circuits. A smart card or microprocessor cards contain volatile memory and microprocessor components. The card is made of plastic, generally polyvinyl chloride, but sometimes acrylonitrile...
s, set-top box
Set-top box
A set-top box or set-top unit is an information appliance device that generally contains a tuner and connects to a television set and an external source of signal, turning the signal into content which is then displayed on the television screen or other display device.-History:Before the...
es and other devices that use digital rights management
Digital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...
. In this case the issue is not about stopping the user from breaking the equipment or hurting themselves, but about either stopping them from extracting codes or acquiring and saving the decoded bitstream. This is usually done by having lots of features on each chip and making sure the busses between chips are encrypted.
DRM mechanisms also use certificates and asymmetric Key cryptography in many cases. In all such cases, tamper resistance means not allowing access to the valid device certificates/ public-private keys of the device to the device user. The process of making software robust against tampering attacks is referred to as software anti-tamper.
Nuclear industry
Nuclear reactors that are intended to be sold to countries that otherwise do not possess nuclear weapons need to be made tamper-resistant to prevent nuclear proliferation. For example the proposed SSTARSSTAR
SSTAR is an acronym for the "small, sealed, transportable, autonomous reactor" - being primarily researched and developed in the USA by Lawrence Livermore National Laboratory. It is designed as a fast breeder nuclear reactor that is passively safe...
will feature a combination of anti-tamper techniques that will make it difficult to get at the nuclear material, ensure that where the reactors are transported to is closely tracked, and have alarms in place that sound if attempts at entry are detected (which can then be responded to by the military).
Packaging
Resistance to tampering can be built in or added to packaging. Examples include:- Extra layers of packaging (no single layer or component is "tamper-proof")
- Packaging which requires tools to enter
- Extra strong and secure packaging
- Packages which cannot be resealed
- Tamper-evidentTamper-evidentTamper-evident describes a device or process that makes unauthorized access to the protected object easily detected. Seals, markings or other techniques may be tamper indicating.-Tampering:...
seals and features
The tamper resistance of packaging can be evaluated by consultants and experts in the subject. Also, comparisons of various packages can be made by careful field testing of the lay public.
Software
Software is also said to be tamper-resistant when it contains measures to make reverse engineeringReverse engineering
Reverse engineering is the process of discovering the technological principles of a device, object, or system through analysis of its structure, function, and operation...
harder, or to prevent a user from modifying it against the manufacturer's wishes (removing a restriction on how it can be used, for example). One commonly used method is code obfuscation
Obfuscated code
Obfuscated code is source or machine code that has been made difficult to understand for humans. Programmers may deliberately obfuscate code to conceal its purpose or its logic to prevent tampering, deter reverse engineering, or as a puzzle or recreational challenge for someone reading the source...
.
However, effective tamper resistance in software is much harder than in hardware, as the software environment can be manipulated to near-arbitrary extent by the use of emulation.
If implemented, trusted computing
Trusted Computing
Trusted Computing is a technology developed and promoted by the Trusted Computing Group. The term is taken from the field of trusted systems and has a specialized meaning. With Trusted Computing, the computer will consistently behave in expected ways, and those behaviors will be enforced by...
would make software tampering of protected programs at least as difficult as hardware tampering, as the user would have to hack the trust chip to give false certifications in order to bypass remote attestation and sealed storage. However, the current specification makes it clear that the chip is not expected to be tamper-proof against any reasonably sophisticated physical attack; that is, it is not intended to be as secure as a tamper-resistant device.
A side effect of this is that software maintenance gets more complex, because software updates need to be validated and errors in the upgrade process may lead to a false-positive triggering of the protection mechanism.
See also
- Tamper-evidentTamper-evidentTamper-evident describes a device or process that makes unauthorized access to the protected object easily detected. Seals, markings or other techniques may be tamper indicating.-Tampering:...
devices - 1982 Chicago Tylenol murders1982 Chicago Tylenol murdersThe Chicago Tylenol murders occurred when seven people died after taking pain-relief medicine capsules that had been poisoned. The poisonings, code-named TYMURS by the Federal Bureau of Investigation, took place in late 1982 in the Chicago area of the United States.These poisonings involved...
- Packaging and labellingPackaging and labellingPackaging is the science, art, and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of design, evaluation, and production of packages. Packaging can be described as a coordinated system of preparing goods for transport,...
- Package pilferagePackage pilferagePilferage is the theft of part of the contents of a package. It may also include theft of the contents but leaving the package, perhaps resealed with bogus contents. Small packages can be pilfered from a larger package such as a shipping container...
- FIPS 140-2FIPS 140-2The Federal Information Processing Standard Publication 140-2, , is a U.S. government computer security standard used to accredit cryptographic modules. The title is Security Requirements for Cryptographic Modules...
- Child-resistant packagingChild-resistant packagingChild-resistant packaging or C-R packaging is special packaging used to reduce the risk of children ingesting dangerous items. This is often accomplished by the use of a special safety cap. It is required by regulation for prescription drugs, over-the-counter medications, pesticides, and household...
- Wrap rageWrap rageWrap rage, also called package rage, is the common name for heightened levels of anger and frustration resulting from the inability to open hard-to-remove packaging, particularly some heat sealed plastic blister packs and clamshells...