System for structured encryption of payment card track data with additional security data

A system may include a point-of-sale system that gathers payment card track data from a payment card and a payment gateway that processes the track data to authorize purchase transactions. Discretionary data in a discretionary field of the track data may be compressed to create space that may be used to accommodate additional security data. The sensitive information may be moved to the discretionary field. The compressed discretionary data and the sensitive information may be encrypted using a structure preserving encryption algorithm and a managed encryption key. The managed encryption key or other additional security data may be added the discretionary field. Track data that has been modified in this way may be conveyed to the payment gateway for processing. The payment gateway may extract the key management data, decrypt the encrypted data, and reconstruct the original track data by decompressing the discretionary data and replacing the sensitive track data.