Tokenization: Use Cases, Part 3

By Adrian Lane

Not every use case for tokenization involves PCI-DSS. There are equally compelling implementation options, several for personally identifiable information, that illustrate different ways to deploy token services. Here we will describe how tokens are used to replace Social Security numbbers in human resources applications. These services must protect the SSN during normal use by employees and third party service providers, while still offering authorized access for Human Resources personnel, as well as payroll and benefits services.

In our example an employee uses an HR application to review benefits information and make adjustments to their own account. Employees using the system for the first time will establish system credentials and enter their personal information, potentially including Social Security number. To understand how tokens work in this scenario, let’s map out the process:

  1. The employee account creation process is started by entering the user’s credentials, and then adding personal information including the Social Security number. This is typically performed by HR staff, with review by the employee in question.
  2. Over a secure connection, the presentation server passes employee data to the HR application. The HR application server examines the request, finds the Social Security number is presnt, and forwards the SSN to the tokenization server.
  3. The tokenization server validates the HR application connection and request. It creates the token, storing the token/Social Security number pair in the token database. Then it returns the new token to the HR application server.
  4. The HR application server stores the employee data along with the token, and returns the token to the presentation server. The temporary copy of the original SSN is overwritten so it does not persist in memory.
  5. The presentation server displays the successful account creation page, including the tokenized value, back to the user. The original SSN is overwritten so it does not persist in token server memory.
  6. The token is used for all other internal applications that may have previously relied on real SSNs.
  7. Occasionally HR employees need to look up an employee by SSN, or access the SSN itself (typically for payroll and benefits). These personnel are authorized to see the real SSN within the application, under the right context (this needs to be coded into the application using the tokenization server’s API). Although the SSN shows up in their application screens when needed, it isn’t stored on the application or presentation server. Typically it isn’t difficult to keep the sensitive data out of logs, although it’s possible SSNs will be cached in memory. Sure, that’s a risk, but it’s a far smaller risk than before.
  8. The real SSN is used, as needed, for connections to payroll and benefits services/systems. Ideally you want to minimize usage, but realistically many (most?) major software tools and services still require the SSN – especially for payroll and taxes.

Applications that already contain Social Security numbers undergo a similar automated transformation process to replace the SSN with a token, and this occurs without user interaction. Many older applications used SSN as the primary key to reference employee records, so referential key dependencies make replacement more difficult and may involve downtime and structural changes.

Note than as surrogates for SSNs, tokens can be formatted to preserve the last 4 digits. Display of the original trailing four digits allows HR and customer service representatives to identify the employee, while preserving privacy by masking the first 5 digits. There is never any reason to show an employee their own SSN – they should already know it – and non-HR personnel should never see SSNs either. The HR application server and presentation layers will only display the tokenized values to the internal web applications for general employee use, never the original data.

But what’s really different about this use case is that HR applications need regular access to the original social security number. Unlike a PCI tokenization deployment – where requests for original PAN data are somewhat rare – accounting, benefits, and other HR services regularly require the original non-token data. Within our process, authorized HR personnel can use the same HR application server, through a HR specific presentation layer, and access the original Social Security number. This is performed automatically by the HR application on behalf of validated and authorized HR staff, and limited to specific HR interfaces. After the HR application server has queried the employee information from the database, the application instructs the token server to get the Social Security number, and then sends it back to the presentation server.

Similarly, automated batch jobs such as payroll deposits and 401k contributions are performed by HR applications, which in turn instruct the token server to send the SSN to the appropriate payroll/benefits subsystem. Social Security numbers are accessed by the token server, and then passed to the supporting application over a secured and authenticated connection. In this case, the token appears seen at the presentation layer, while third party providers receive the SSN via proxy on the back end.

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