Secure and fast aggregation of financial data in cloud-based expense tracking applications

Tracking expenses is a task performed in homes and businesses worldwide; for personal finances, the practice of organizing receipts for refunds or summarizing its contents for purposes such as budget planning and tax submission, has been recently aided by different services; these allow automatic collection of receipts either at store terminals or using a photo of the receipt submitted by the user, which can be later accessed using an online interface. Given the importance of financial information and the inherent danger introduced by these services, we present in this article an architecture based on additive homomorphic cryptosystems and secret sharing schemes to store information securely while still allowing fast aggregation queries at an outsourced untrusted cloud server. The proposal was evaluated in terms of security, server load, amount of user interaction, computational load at the acquiring terminal and computational load at the untrusted server.