MIFARE Fare Card Batch Integrity Investigation

Identified a systematic mapping mismatch affecting approximately 125,000 MIFARE fare cards, isolated the affected inventory, supported its warranty replacement, and introduced a validation process that prevented recurrence.

Key Outcomes

125,000
Affected fare cards identified
Warranty Recovery
Affected inventory replaced
Validation Control
Incoming-batch verification introduced
No Recurrence
Same issue did not recur after implementation

Context and Responsibility

My responsibilities within Metro Santo Domingo's Automated Fare Collection system included system maintenance, system security, technical auditing, maintenance projects, inventory and stock control, fare-card supplies, and investigation of operational incidents.

Operational Problem

  • A manufacturer supplied batches of MIFARE fare cards together with an identifier relationship file for loading card records into the fare-collection backend.
  • After an apparent sequence error in one batch, a significant portion of the relationship data became offset by one position from the physical cards.
  • Information associated with one physical card could appear under another card in the system.
  • Administrative actions, including blocking a card, could affect a different card because physical assets and backend records no longer matched correctly.

Investigation

System Data Review

Analyzed card, transaction, and system information to determine where physical cards and backend records diverged.

Physical Card Testing

Read sample cards with card readers and recorded their physical card identifiers for direct comparison.

Three-Way Validation

Compared physically read identifiers with the manufacturer-provided relationship file and the records loaded into the fare-collection backend.

Root-Cause Identification

The verified finding was a repeatable sequential mapping offset rather than random card failures. The pattern appeared after an apparent sequence error in the supplied batch and relationship data, explaining why information and administrative actions could be associated with the wrong physical card.

Scope of Affected Inventory

Using the identified pattern, I reviewed the fare-card inventory held in storage and the affected lots. Approximately 125,000 fare cards were identified as affected by the identifier mapping mismatch.

Corrective Action and Warranty Recovery

Inventory Isolation

The affected cards were identified and separated so they would not be released for operational use.

Technical Claim Support

The physical tests, data comparisons, and sequential mismatch pattern formed the technical basis of the warranty claim.

Replacement Inventory

The manufacturer accepted the affected inventory under warranty and supplied replacement cards rapidly enough to reduce operational disruption.

Incoming Batch Validation Control

The incident was converted into a repeatable acceptance control for future deliveries. Each received lot was independently checked before its relationship data was released for backend loading, using samples selected from different boxes and areas of the lot.

  1. Physically read each sampled card using a card reader.
  2. Record the card identifier or reference.
  3. Create a manual comparison sample.
  4. Compare the physically read identifiers with the manufacturer-supplied relationship file.
  5. Verify the batch before releasing it for operational use.

Accessible process diagram

Investigation to Control

The investigation connected physical samples to system records, then converted the verified finding into inventory action and a permanent receiving control.

Physical-to-Digital Reconciliation

  1. 01Physical Card
  2. 02Card Identifier Read
  3. 03Manufacturer Relationship File
  4. 04Backend Record

Incident-to-Control Sequence

  1. 01Operational anomaly
  2. 02Physical card sampling
  3. 03Identifier reading
  4. 04Manufacturer file comparison
  5. 05Sequential offset identified
  6. 06125K affected cards isolated
  7. 07Warranty replacement
  8. 08Incoming-batch validation control

Results and Operational Value

  • Approximately 125,000 affected cards were identified.
  • The systematic identifier mapping mismatch and its sequence pattern were established.
  • The affected inventory was successfully claimed and replaced under manufacturer warranty.
  • A repeatable incoming-batch sampling and identifier-validation process was implemented.
  • The same issue did not recur after the new validation process was introduced.

Operational Change

Future card deliveries were no longer released based only on the supplied relationship file. Each lot was sampled, the physical card identifiers were compared with the file, and the batch was verified before operational use. The same mapping issue did not recur after this control was introduced.