fairCASH - the first true digital cash solution

Pairing is a temporary coupling association between two peers to establish a connection for a monetary value data exchange transfer. The selection of how to make a payment transaction depends on two facts:

  • the type of available physical communication interface(s) and
  • the distance between both parties entering into a transaction.

Users of the fairCASH system have the choice to transfer money within a face-to-face (proximity) or long distance (remote) scenario. The transaction partner can be either a service or another eWallet. Logical pairing methods are used in the starting phase of any fCCP communication. The execution of connectionless logical pairing provides a solution to the question how being able to build the right couple of two parties, even if they never met before. To achieve that, we need a way of separating our couple from the crowd. In cases the initiator knows the unique name, address (for In-Band (IB) methods) or is able to use an Out-of-Band (OoB) association model for the device discovering process, a request can be send to the responder to initiate and establish the pairing. During the pairing phase both devices – the eWallet’s of the principals – are using the device-identifying reference. This can be a MAC-ID, MSN or a peer address in the communication network, where the pairing takes place. At the end of the pairing phase both paired peers mutually know their logical addresses which they need inevitably for the next communication phases of the protocol (in case of a successful pairing phase).

Payments for goods or services initiated from an eWallet based mobile phone, PDA or any other (mobile) device are termed mPayment. In consistency with the public definition of the banking industry there are two kinds of mobile payments:

  • proximity mobile payments (e.g. at the physical PoS) and
  • remote mobile payments (e.g. in the Internet).

Most mobile eWallets are expected to be used in combination with a Smartphone. As they may be equipped with various types of communication interfaces, a flexible adaptation is needed to make them usable as communication channel for fCCP. Our figure depicts the possibilities being available to set up such connection using different pairing constellations:

How the pairing can be done within fairCASH.
How the pairing can be done within fairCASH.

Out-of-Band (OoB) Method

The OoB association model is designed for scenarios where such a mechanism supports a connection operation including a two-way mutual authentication. Such a two-way communication needs to be available to both parties – not only for discovering other partner devices, but as well for mutual exchanging their identification device names. The name comes from the fact, that OoB uses a second – separate – other channel than for the later payload for this purposes. RFID-based solutions are the usual way for this issue. For example, a Near Field Communication (NFC) equipped device needs only to touch the other NFC device and the pairing is done. This is a single touch experience where information is exchanged between both devices, including discovery information such as certificates, MAC- and IP-IDs of both devices as well as some cryptographic functionality for a protocol-run to be unique making this pairing method safe against Man-In-The-Middle-Attacks (MITMA). Once the devices know each other, the establishment of the VPN/VPC tunnel follows then in-band.

In-Band (IB) Method

In all cases where the initiator already knows a way to reach the other device using a native device address of the responder it can easily use the same communication channel (so called IB) as used later for the payload to specify the Internet address (IP) or a telephone number (MSN) to inquire the targeted device and create a pairing association.


Short-range wireless or proximity mobile payments are defined as wireless payment operations ranging in a broadcast-domain ad hoc topology. Most proximity mobile payments are expected to be made at both attended Point-of-Sale (PoS) locations (such as stores) and unattended locations (such as vending machines) using an existing merchant’s payment infrastructure, including local direct peer-to-peer connections between two gadgets with their attached eWallets. To pay, the user simply brings his mobile eWallet with the other user’s eWallet or the contactless payment enabled Point-of-Sale (PoS) system within a few inches together and the transaction occurs. The technical range of a proximity system is below 10 meters, the NFC range not more than 10 cm. This is the case if someone is shopping in a mall wanting to checkout with selected goods at a Point-of-Sale (PoS).


Long-range wireless or remote mobile payments are defined as wireless payment operations ranging in a single-cast environment by phone number and/or MAC/IP identification. Practical use cases for remote mobile payments may include purchases from a web merchant or payments for digital goods. Remote mobile payments are ideal for use in markets that require person-to-person payments and for under banked consumers and merchants. To transfer money a user simply initiates an Internet connection using his mobile gadget and the other authorizes the transfer. In contrast to the previous local model, the scope of a remote payment is global. This payment situation arises if both peers have to connect over long distance. In such situations the Internet, mobile radio services, or leased line based networks are mostly used.

In contrast to others it does not matter how far the two entities are apart from each other: No transfer charges to the fairCASH service apply. fairCASH systems adapts to systems like eMail and others. All these are operating on a global scope, most of them with flat rates.