Over the air update of payment transaction data stored in secure memory

A mobile device for use in conducting a payment transaction, comprising:

• a processor;
• a computer readable memory;
• and
• a set of instructions stored in the computer readable memory, which when executed by the processor implement a method comprising:
• conducting the payment transaction by communicating with a point of sale terminal over a first communication channel using a contactless element in the mobile device, and adjusting an accumulator stored in the mobile device by an initial transaction amount of the payment transaction;
• receiving an encryption key to be used for encrypting and decrypting transaction data over a second communication channel from a mobile gateway associated with an encryption key server in response to conducting the payment transaction, the encryption key being generated by the encryption key server based on a request associated with the payment transaction, the second communication channel being different than the first communication channel, and the second communication channel utilizing a cellular communications network;
• receiving encrypted data related to the payment transaction in response to conducting the payment transaction, the encrypted data comprising an actual transaction amount at the mobile device through the second communication channel after communicating with the point of sale terminal, wherein the actual transaction amount of the payment transaction is determined by the point of sale terminal modifying the initial transaction amount of the payment transaction;
• decrypting the encrypted data related to the payment transaction using the encryption key;
• and
• updating the accumulator stored in the mobile device using the decrypted data related to the payment transaction, the decrypted data comprising the actual transaction amount of the payment transaction such that the accumulator is adjusted by the difference between the actual transaction amount of the payment transaction and the initial transaction amount of the payment transaction.