Nowadays, Near Field Communication (NFC) technology is being experimented for payment systems to perform purchase transactions without physical contact, without entering a PIN code or a signature. An NFC purchase transaction is mainly executed between a client's payment device (NFC bank card or NFC smartphone) and a merchant's payment device. The latter may be either an NFC point of sale machine for big traders (in a department store for example), or a simple NFC payment terminal attached to the outside of a smartphone for small traders. In this paper, we propose a new secure cloud-based NFC payment architecture for small traders: which allows them to benefit from their smartphones integrating NFC technology for use directly as NFC merchant payment devices, without needing to buy an external NFC payment terminal. In addition, the proposal introduces a new protocol aiming to secure NFC payment transactions.