fairCASH - the first true digital cash solution

A fairCASH deal has the following definition:

  • Two prospective signatory entities mutually known sign a certain contract:
  • Seller 'explains exchange' between 'goods or services' and 'payment' to buyer by invoice,
  • Buyer 'explains exchange' by the payment transfer,
  • Seller 'explains' the successful payment transfer to buyer by receipt,
  • fCCP makes the transfer non-repudiational for both parties.
Transaction sequence of fCCP in a message oriented form.
Transaction sequence of fCCP in a message oriented form.

Pairing phase
This is the pairing partnership association phase. Both entities enter into a P2P-based transaction relationship by mutually identify themselves:

  • The initiator uses the application software to enter information about his action and creates the request.
  • The initiator determines the method (there are different technical methods to do that, e.g. by using an NFC/RFID, a DNS/IP entry or a MSN) for contacting the other peer using a proximity or remote connection.
  • The initiating eWallet contacts the target eWallet.
  • Both eWallets exchange their certificates.

VPN/VPC setup phase
This is the setup phase for the VPN/VPC-session-initiation. A virtual private network or channel is being established:

  • Both eWallets exchange key information.
  • Both eWallets negotiate a VPN/VPC.

Negotiation phase
Both eWallets negotiate the intended deal. Part of this policy based checking process is the verification of enough value availability and other rules:

  • Both eWallets exchange their user certificates.
  • Both eWallets specify and acknowledge the deal.
  • Both eWallets compare the other’s eWallet identity with the intended one.
  • Both eWallets authorize or decline the deal.

Value data transfer
The payment is exchanged against an electronic receipt:

  • The eCoins of the main payment are transferred.
  • The eCoins of the change payment are transferred.

Confirmation phase
Both parties receive their irrefutable evidences to make the deal complete, repudiation-free and final (with the weak deal exception):

  • The acknowledge tickets are sent.
  • Both eWallets inform their respective users about the money transfer status.
  • Both eWallets terminate the connection.

State-Transitions of an eWallet Node

The following figure shows the state-flow transition-logic of a single eWallet-node. It is vitally important to keep in mind that fCCP works by atomizing the asynchronous exchange-process. That means: Operations are protected either to be completely done or not at all. It makes our protocol durable and guarantees the reliable consistency processing. Our considered instruments to achieve security are the logical embracement of operations, which are to be atomized with the implementation of internal, and invisible ‘Enter’ and ‘Leave’ transaction-tokens, followed by a ‘Commit’ or undoing it with a ‘Rollback’:

Mealy state-machine (FSM) transition-flow of an eWallet.
Mealy state-machine (FSM) transition-flow of an eWallet.

Execution transaction times for selected networks

A source of arrested attention for every payment system is the average transaction duration. Exemplary transaction time calculations for several network usage cases are listed in following table:

Transaction protocol runtime calculations for different networks.
Network Name Uplink Speed Round Trip Time Processing Time Run Time
RFID/NFC 106 kbit/s 64 kbit/s 20 ms 100 ms 5.7 s
RFID/NFC 212 kbit/s 127 kbit/s 20 ms 100 ms 3.4 s
RFID/NFC 424 kbit/s 256 kbit/s 20 ms 100 ms 2.3 s
RFID/NFC 848 kbit/s 352 kbit/s 20 ms 100 ms 1.9 s
RFID/NFC 6,78 Mbit/s 2.7 Mbit/s 20 ms 100 ms 1.2 s
RFID/NFC 13,56 Mbit/s 5.4 Mbit/s 20 ms 100 ms 1.2 s
GSM Standard CSD (Circuit Switched Data) 9.6 kbit/s 900 ms 100 ms 38.2 s
GPRS 25.6 kbit/s 1000 ms 100 ms 17.5 s
ISDN 62 kbit/s 200 ms 100 ms 6.7 s
UMTS Standard 51.2 kbit/s 400 ms 100 ms 8.7 s
EDGE (Enhanced Data Rates for GSM Evolution) 88 kbit/s 1865 ms 100 ms 13.7 s
T-DSL 2048/192 163 kbit/s 55 ms 100 ms 3.1 s
HSPA (High Speed Packet Access) 1.2 Mbit/s 260 ms 100 ms 2.5 s
HSUPA (High Speed Uplink Packet Access) Cat.2 1.2 Mbit/s 50 ms 100 ms 1.5 s
Bluetooth 2.0+EDR 2.0 Mbit/s 10 ms 100 ms 1.2 s
HSDPA (High Speed Downlink Packet Access) 5.8 Mbit/s 150 ms 100 ms 1.8 s
HSPA+ 8.8 Mbit/s 100 ms 100 ms 1.5 s
WLAN IEEE 802.11g 20 Mbit/s 10 ms 100 ms 1.1 s
LTE (Long Term Evolution) or HSOPA (High Speed OFDM Packet Access) Basic 40 Mbit/s 25 ms 100 ms 1.1 s
Fast Ethernet 80 Mbit/s 1 ms 100 ms 1.0 s
WLAN IEEE 802.11n 100 Mbit/s 10 ms 100 ms 1.1 s
Giga Ethernet 800 Mbit/s 1 ms 100 ms 1.0 s