Sensitive Data and Types of Disclosures

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Sensitivity of data is a measure of the importance assigned to the data by its owner, for the purpose of denoting its need for protection. Some databases contain only sensitive data while other databases may contain no sensitive data at all. Handling databases that fall at these two extremes is relatively easy, because these can be covered by access control, which is explained in the next section. The situation becomes tricky when some of the data is sensitive while other data is not.

Several factors can cause data to be classified as sensitive:

1. Inherently sensitive. The value of the data itself may be so revealing or confidential that it becomes sensitive—for example, a person’s salary or that a patient has HIV/AIDS.

2. From a sensitive source. The source of the data may indicate a need for secrecy—for example, an informer whose identity must be kept secret.

3. Declared sensitive. The owner of the data may have explicitly declared it as sensitive.

4. A sensitive attribute or sensitive record. The particular attribute or record may have been declared sensitive—for example, the salary attribute of an employee or the salary history record in a personnel database.

5. Sensitive in relation to previously disclosed data. Some data may not be sensitive by itself but will become sensitive in the presence of some other data—for example, the exact latitude and longitude information for a location where some previously recorded event happened that was later deemed sensitive.

It is the responsibility of the database administrator and security administrator to collectively enforce the security policies of an organization. This dictates whether access should be permitted to a certain database attribute (also known as a table column or a data element) or not for individual users or for categories of users. Several factors need to be considered before deciding whether it is safe to reveal the data. The three most important factors are data availability, access acceptability, and authenticity assurance.

1. Data availability. If a user is updating a field, then this field becomes inaccessible and other users should not be able to view this data. This blocking is only temporary and only to ensure that no user sees any inaccurate data. This is typically handled by the concurrency control mechanism (see Chapter 22).

2. Access acceptability. Data should only be revealed to authorized users. A database administrator may also deny access to a user request even if the request does not directly access a sensitive data item, on the grounds that the requested data may reveal information about the sensitive data that the user is not authorized to have.

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3. Authenticity assurance. Before granting access, certain external characteristics about the user may also be considered. For example, a user may only be permitted access during working hours. The system may track previous queries to ensure that a combination of queries does not reveal sensitive data. The latter is particularly relevant to statistical database queries (see Section 24.5). The term precision, when used in the security area, refers to allowing as much as possible of the data to be available, subject to protecting exactly the subset of data that is sensitive. The definitions of security versus precision are as follows:

? Security: Means of ensuring that data is kept safe from corruption and that access to it is suitably controlled. To provide security means to disclose only nonsensitive data, and reject any query that references a sensitive field.

? Precision: To protect all sensitive data while disclosing as much nonsensitive data as possible.

The ideal combination is to maintain perfect security with maximum precision. If we want to maintain security, some sacrifice has to be made with precision. Hence there is typically a tradeoff between security and precision.  

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