Provided is a computer-implemented method for conducting a payment transaction to ensure data integrity of the payment transaction that includes generating a transaction authorization request message, where the transaction authorization request message comprises a payload associated with an electronic funds transfer at a point-of-sale (POS) device, and where generating the transaction authorization request message includes generating a digital signature for the payload using a private key of a payment gateway system and inserting the digital signature for the payload into the transaction authorization request message, transmitting the transaction authorization request message including the digital signature, and receiving a transaction authorization response message from a transaction service provider system. A system and computer program product are also provided.