Frequently Asked Question

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

In order to meet PCI DSS Requirement 3.4, entities with both hashed and truncated versions of a PAN in their environment are also required to implement additional 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 different values
  • Use of separate storage systems, one for hashed and one for truncated PANs, that are isolated from each another using segmentation, separate access controls, etc.
  • Configuring file/database systems 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.
Originally published: November 2014
Article Number: 1308

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