Algorithms

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Substitution

Substitution masks data by replacing a given value with another value suitable for the given entity, be it a field or part of the text or any other type of an entity. Substitution could be random or pseudo-random, could preserve referential integrity and statistical distribution or disturb it, and could deal with the whole, at-once, value replacements or complex replacement patterns of the parts of the entity.

In mathematical terms, the substitution method of data masking allows mapping of members of one set to the members of another set, such that the members of replacing set are of the same intensional definition.

Random

Random substitution masks data by replacing a given value with a random value from a pre-compiled data set. Values in the data set are suitable and conform to the same rules or definitions that of the given value. With each iteration of the masking algorithm, another random value gets chosen and replaces the value on the input. An example would be a value of John being masked with values of Alex, Robert, and Mike in subsequent iterations of the substitution operation.

As data masking of the given value with Random Substitution does not guarantee to be repeatable among cycles, it is not suitable for masking data sets with unique constraints and requires extra work of preserving referential integrity if used on the values of fields preserving referential integrity constraint. In denormalized data sets it might cause difficulties in implementing row-internal synchronization, table internal synchronization and table-to-table synchronization operations.

Preserving Referential Integrity

These are algorithms that mask data by replacing a given value with a pseudo-random value from a pre-compiled data set. The "pseudo" comes from the fact that there is an underlying algorithm that matches a given value to the very same value at each iteration of the substitution operation.

An example would be a value of a name Jane always masked with the value of the name Virginia. Such substitution allows for better preservation of referential integrity as well as for synchronization of values among cells in the same and different tables and in the text.

Replacing sets in the substitution data masking algorithm could have the same numbers of values as original sets ( the same cardinality) or different number of values.

Disturbing Statistics

For certain types of de-identified data, its statistics becomes security's "enemy". Such examples were identified by Dr. Latanya Sweeney , then graduate student, today's Harvard's professor with specialization in computer science and privacy. She identified such data and HIPAA's famous 18 elements list some of them: zip codes, dates of births, as well as the rules that allow to change this statistics. When a subtype of substitution data masking technique matches data sets with the same cardinality (the same number of elements), one to one, the statistical distribution of the resulting set values is completely preserved. If there exists a public data set and/or its statics is in the public domain, someone knowing the statistics could re-identify the de-identified data. An example of such risk is explained in the webinar. You could also see how easy/hard it is to find out the risk of identifying you statistically : How Unique Are You? Thus, it is important to make sure that "statistics" is disturbed, by changing set cardinalities or providing the algorithms that change statistical distributions ( patent pending).

Unique

Some of the data is designed to be unique. Its statistical value is insignificant in the paradigm of the re-identification risks.

The representative elements of such data are those that have one value per person or household: social security, passport, credit card, and phone numbers are prime examples.

They are unique within the context. As such, it is important often in code to replace them with other unique values of the same format, but not belonging to that particular person.

E.g. American phone number shell retain one of the formats defined by North American Numbering Plan (NANP), such as xxx- xxx-xxxx or +1 (xxx) xxx xx xx

For de-identifying the unique elements, several methods are used, including unique substitution, shuffling, and format preserving encryption.

Character Permutation and Character Substitution

Two algorithms that manipulate character of a given string.

The character permutation data masking algorithm uses characters of a given string as an input set and maps this set on itself by creating various permutations of the characters of the string either randomly or in pre-defined repeatable pattern.

The character substitution data masking algorithmalgorithm, besides a given string value, uses another set of the characters with the specific mapping rules, creating an output based on either random or predefined mappings.

The strongest masking algorithm of this variety is random character substitution, followed by random character permutation and pre-defined character substitution, followed by pre-defined character permutation.

Format Preserving Encryption

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Shuffle

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Date Variance

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Number Variance

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Nulling

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