cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adver ...

, zeroisation (also spelled zeroization) is the practice of erasing sensitive parameters (electronically stored data,

cryptographic key A key in cryptography is a piece of information, usually a string of numbers or letters that are stored in a file, which, when processed through a cryptographic algorithm, can encode or decode cryptographic data. Based on the used method, the key c ...

s, and critical security 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.

Mechanical

When

encryption In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decip ...

was performed by mechanical devices, this would often mean changing all the machine's settings to some fixed, meaningless value, such as

zero 0 (zero) is a number representing an empty quantity. In place-value notation Positional notation (or place-value notation, or positional numeral system) usually denotes the extension to any base of the Hindu–Arabic numeral system (or ...

. On machines with letter settings rather than

numerals A numeral is a figure, symbol, or group of figures or symbols denoting a number. It may refer to: * Numeral system used in mathematics * Numeral (linguistics), a part of speech denoting numbers (e.g. ''one'' and ''first'' in English) * Numerical d ...

, the letter 'O' was often used instead. Some machines had a button or lever for performing this process in a single step. Zeroisation would typically be performed at the end of an encryption session to prevent accidental disclosure of the keys, or immediately when there was a risk of capture by an adversary.

Software

In modern

software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consists ...

based cryptographic modules, zeroisation is made considerably more complex by issues such as

virtual memory In computing, virtual memory, or virtual storage is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a very l ...

compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...

optimisation Mathematical optimization (alternatively spelled ''optimisation'') or mathematical programming is the selection of a best element, with regard to some criterion, from some set of available alternatives. It is generally divided into two subfi ...

s and use of

flash memory Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Both us ...

. Also, zeroisation may need to be applied not only to the key, but also to a

plaintext In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted. Overview With the advent of comp ...

and some intermediate values. A cryptographic software developer must have an intimate understanding of

memory management Memory management is a form of resource management applied to computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and free it for reuse when ...

in a machine, and be prepared to zeroise data whenever a sensitive device might move outside the security boundary. Typically this will involve overwriting the data with zeroes, but in the case of some types of

non-volatile storage Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data. Non-volatile memory typic ...

the process is much more complex; see ''

data remanence Data remanence is the residual representation of digital data that remains even after attempts have been made to remove or erase the data. This residue may result from data being left intact by a nominal file deletion operation, by reformatting o ...

''. As well as zeroising data due to memory management, software designers consider performing zeroisation: * When an application changes mode (e.g. to a test mode) or user; * When a

computer process In computing, a process is the instance of a computer program that is being executed by one or many threads. There are many different process models, some of which are light weight, but almost all processes (even entire virtual machines) are ro ...

changes privileges; * On termination (including abnormal termination); * On any error condition which may indicate instability or tampering; * Upon user request; * Immediately, the last time the parameter is required; and * Possibly if a parameter has not been required for some time. Informally, software developers may also use zeroise to mean any overwriting of sensitive data, not necessarily of a cryptographic nature.

Tamper resistant hardware

tamper resistant Tamperproofing, conceptually, is a methodology used to hinder, deter or detect unauthorised access to a device or circumvention of a security system. Since any device or system can be foiled by a person with sufficient knowledge, equipment, and ti ...

hardware, automatic zeroisation may be initiated when tampering is detected. Such hardware may be rated for cold zeroisation, the ability to zeroise itself without its normal

power supply A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a r ...

enabled.

Standards

Standards for zeroisation are specified in

ANSI The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...

X9.17 and

FIPS 140-2 The Federal Information Processing Standard Publication 140-2, (FIPS PUB 140-2), is a U.S. government computer security standard used to approve cryptographic modules. The title is ''Security Requirements for Cryptographic Modules''. Initial publ ...

References

{{reflist Key management