Achieving Optimal Anonymity in Transferable E-Cash with a Judge

Abstract

Abstract. Electronic cash (e-cash) refers to money exchanged electronically. The main features of traditional cash are usually considered desirable also in the context of e-cash. One such property is off-line transferability, meaning the recipient of a coin in a transaction can transfer it in a later payment transaction to a third person without contacting a central authority. Among security properties, the anonymity of the payer in such transactions has been widely studied. This paper proposes the first efficient and secure transferable e-cash scheme with the strongest achievable anonymity properties, introduced by Canard and Gouget. In particular, it should not be possible for adversaries who receive a coin to decide whether they have owned that coin before. Our proposal is based on two recent cryptographic primitives: the proof system by Groth and Sahai, whose randomizability enables strong anonymity, and the commuting signatures by Fuchsbauer, which allow one to sign values that are only given as encryptions.

Security of Offline Anonymous Electronic Cash Systems against Insider Attacks by Untrusted Authorities Revisited

“…Blazy et al [13] investigated offline transferability. The property called offline transferability means that the recipient of an e-cash can transfer it to another person without contacting any authority.…”

“…The property called offline transferability means that the recipient of an e-cash can transfer it to another person without contacting any authority. In [13], a trusted authority called judge is introduced and the judge can extract the identity of a doublespender after the bank detects the double spending. In [13], a customer generates its own pair of public and private keys and obtains a certificate from the judge.…”

“…Following the classification of Miyazaki and Sakurai, we investigate some of the recently proposed electronic cash systems such as [7], [8], [10]- [13].…”

Analysis of Security Issues in Electronic Payment Systems

“…In this electronic payment system, tokens are the payment instruments that represent monetary values. A customer must install a "cyber wallet" onto his computer, which will store the money requested from the bank, [4].…”

Divisible E-Cash in the Standard Model

“…Independently, Fuchsbauer, Pointcheval and Vergnaud also used Groth-Sahai proofs [30] to build a transferable fair (i.e., involving a semitrusted third party) e-cash system in the standard model. More recently, Blazy et al [7] gave a similar construction with stronger anonymity properties.…”