Enhanced fair micropayment scheme based on hash chain to avoid merchant collusion

Yang, Lang and Tan recently introduced a new fair micropayment scheme that the customer can withdraw a hash chain to make the transactions with different merchants. The secrecy of this scheme will be compromised by the merchant collusion; a merchant reveals his anchor of payword chain to other merchants so that other merchants can redeem the hash chains from the bank even the customer does not purchase services. Besides, we propose an enhanced scheme to solve the merchant collusion problem.