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FAQ #1308 Diff

How can an entity ensure that hashed and truncated versions cannot be correlated, as required in PCI DSS Requirement 3.4?

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In order to meet PCI DSS Requirement 3.4, entities3.5.1 states that if hashed and truncated versions of the same PAN, or different truncation formats, are present in the environment, additional controls must be implemented to prevent correlation.

The simplest solution is not to store both hashed and truncated PANs. If both must be retained, the following controls can help:

Use of strong, unique, secret salts for hashing
Separate storage systems for hashed and truncated values, isolated with both hashed and truncated versions of a PAN in their environment are also required to implement additionalsegmentation, and distinct access controls to ensure that the hashed and truncated versions cannot be correlated to reconstruct the original PAN.
The simplest approach for meeting this requirement is to not store hashed and truncated PAN. If, however, an entity wishes to store both hashed and truncated PAN, additional controls are needed to provide assurance that there is no single point where the two types of PAN formats could be captured for correlation. Examples of methods that may be able to meet the intent of this requirement include:
- Use of a unique, strong and secret input variable (e.g. salt) for each hash such that two hashes of the same PAN would have differentPreventing cross-references or database links between values
- Use of separate storage systems, oneReal-time monitoring to detect correlation attempts

These are examples only. Controls should be suitable for hashed and one for truncated PANs,the environment and ensure that are isolated from each another using segmentation, separate access controls, etc.
- Configuring file/database systemsfull PAN reconstruction is not possible.

As per the guidance listed in PCI DSS implementing keyed cryptographic hashes with associated key management processes and procedures in accordance with Requirement 3.5.1.1 is a valid additional control to prevent the existence of any cross-references or links between a hash and a truncated PAN
- Use of real-time monitoring and dynamic response to detect and prevent requests to access correlating PAN values.

These examples are provided as suggestions; entities are not limited to only the above methods. Whichever methods are used, they should prevent unauthorized persons being able to correlate a hashed PAN to a truncated PAN, and be appropriate for the entity?s environment.correlation.

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