Yiannis Tsiounis's research while affiliated with Northeastern University and other places

... Brand introduced a restrictive blind signature scheme where a client provides zero-knowledge proof along with his identity in the resulting blind signature [6,7]. The scheme is inadequate to prevent double spending of e-coin if a malicious user can construct a forged identity and can spend the e-coin multiple times [8]. Fujisaki and Okamoto introduced a partially blind signature to overcome the downsides of carrying public and private keys where bank needs to maintain a huge database of every client [9,10]. ...

... It is related to certain well-known problems [16] such as postagestamp problem, knapsack problem, and change-making problem. The closest one is the k-payment problem [17], which was motivated by electronic cash model, where exact representation of each payment by the corresponding set of coins is required. Our problem, in contrast, is motivated by optical switching, where the hardware cost depends on the size of switching matrix, while the switched wavebands (coins) may or may not be completely occupied by wavelengths (units) unlike the k-payment problem. ...

... Nevertheless, some alternative e-cash systems were proposed that managed to avoid the growth of the e-cash data (D'Amiano and Di Crescenzo, 1994;Okamoto, 1995). However, as mentioned in Chan et al. (1998), Tsiounis (1997), those e-schemes had other issues such as the limit of the total size of payments or lack of efficiency of e-cash protocols. In Fuchsbauer (2009) an attempt was made to construct a transferable e-cash scheme without the aforementioned data growth problem. ...

... We note that revocable anonymity is a concept which has been considered at great length in other fields, such as digital cash [27,28,31,10,17]. In digital cash, it is particularly important that it should be possible to link an electronic coin to the person who spent it once the transaction has occurred (for example, that coin may have been spent twice, or spent illegally). ...

... En la década de los noventa, toma impulso el movimiento Cypherpunk, inspirado en los principios de la anarquía digital y un conocimiento de matemáticas avanzadas, alentando el uso de sistemas criptográficos que permitieran salvaguardar la información personal y la privacidad en los pagos (Cavaller Riva y Ortega Yubro, 2021). Por estos años, nacieron proyectos como B-Money (Brands, 1994) y Bit Gold (Frankel et al., 1996) con la intención de eliminar a los intermediarios en los procesos de negociación. Cabe destacar la iniciativa de David Chaum que en 1990 lanza DigiCash y, posteriormente, eCash, que permitía realizar pagos con dinero electrónico a través de computadoras empleando solamente un software. ...

... The idea of determining whether a committed integer falls within a given range was first proposed in [19] and further expanded in [13,15]. The CFT Proof [16] achieves the goal of demonstrating that a secret value is within a given range. However, the CFT proof has a very high expansion rate. ...

... After double spending, the bank would be able to clear the structure in a polynomial time. Although Brands' scheme suffers from some weaknesses in misrepresenting the identity of the customer [17], some solutions have been proposed to prevent these weaknesses [10] [17]. Afterward, some schemes have been presented, which use a similar method to Bands' restrictive blind signature, to detect the identity of a double spender [18] [19] [20]. ...

... This technology prevented centralized institutions that provide signatures from linking users to their transactions. A series of other digital currency payment technologies like J. Wu et al. universal electronic cash (Okamoto and Ohta, 1991), untraceable offline cash (Brands, 1993), fair blind signatures (Stadler et al., 1995), fair off-line e-cash (Frankel et al., 1996) later emerged in the 1990s. However, a common problem existed in these technologies is that-trusted third parties are needed to detect double spending attacks. ...

... Nevertheless, in 1998, Frankel, Tsiounis and Yung in [26] pointed out that to date, there have been no efficient systems that could offer provable security. They proposed a fair off-line e-cash system, where the trusted third party could revoke the anonymity under a warrant or in the case of specified suspicious activity. ...

... Our scheme adopts credit-based charging, i.e. the system charges each mobile user after it has finished a sequence of services for the user, just as the practical situation in the real world. It is different from the others which provided approaches of debit-based charging, i.e. each mobile user has to purchase payment token(s) before she/he starts accessing the services provided by the system [6,12]. What are the differences between charging mobile users in advance and charging them after the services? ...