The non-repudiation property is essential for our fairCASH system, because of the dispute resolving mechanism we need to recreate fairness. It provides our originator and recipient with valid irrefutable evidence after completion of the protocol, without giving a party an advantage over the other at any stage of the protocol-run, assuming that the communication channel between the both peers is not permanently broken and can be totally insecure.
In general non-repudiation is not an essential requirement for fair exchange protocols, offering payer and payee dispute-free message transmission. It is also part of the out-of-protocol dispute resolving mechanism after a failed transaction that handles occurrence or non-occurrence of a claimed event or action in order to enable the settlement of disputes. Additionally, it satisfies properties such as privacy and anonymity.
Both, the protocol originator, which receives its Non-Repudiation of Receipt (NRR) evidence, and the recipient, which receives his message, and the Non-Repudiation of Origin (NRO) evidence (this process is also called evidence collection during the protocol-run) have that at the end after a correct and complete exchange or none of them receive any valid evidence.
Non-repudiation is composed of four distinct phases:
- the evidence generation,
- the transfer and storage of its messages,
- their verification and
- the disputes resolution.
For example consider the following example scenario of a transaction between two users, referred to as Alice and Bob. Bob, the merchant, wishes to be able to prove that Alice authorized the payment transaction in order to ensure Alice will not attempt to deny it later. He also wants an assurance that Alice has the funds to pay, and that the money will be transferred to him. In some circumstances both, Alice and Bob may also wish to avoid revealing the fact of the transaction against third parties. Meanwhile, Alice wishes to ensure unauthorized payments were impossible, so Bob cannot deny having received her payment, and that the fact of transaction is private. To achieve this every transaction needs to be permanent (finality aspect). That means no one being able to reverse the transaction and take the money back. Nobody will honor any request to undo the transaction performed by an authorized user. The only way of getting the money back is if the recipient spends it back to the originating eWallet. If the payer is uncertain if the payee eWallet’s identification he entered or selected is correct, a direct payee contact for confirmation of the correct eWallet identification is the only way. If there is any reason to doubt whether the payee will deliver the goods or services being promised, a trusted third party (but not our eMint) needs to be engaged to serve as an escrow agent.
Protocols being repudiation free play an important role in mCommerce where participants require mutual guarantees like non-repudiation.