Towards Provably Secure Eecient Electronic Cash (extended Abstract)

An \electronic coin scheme" as deened by Chaum, Fiat, and Naor 5] is a collection of protocols to achieve untraceable, unforgeable coins with ooine purchasing; this is the minimum set of properties to make electronic money useful. We give a new electronic coin scheme that is simple and practical. Withdrawal requires only two rounds of interaction, while purchase and deposit are non-interactive; all previous eecient cash schemes require interaction (cut-and-choose) for purchases. Moreover, messages during purchase and deposit contain only a few encrypted values, independent of the tolerable probability of cheating. We present a security model for electronic coins, and prove the security of our scheme relative to certain speciic cryptographic assumptions (hardness of Discrete Log and possibility of secure blind signature).