International Association
for Cryptologic Research

Compact e-cash schemes allow users to withdraw a wallet containing $K$ coins and to spend each coin unlinkably. We present the first compact e-cash scheme with arbitrary wallet size $k \\leq K$ while the spending protocol is of constant time and space complexity.

Known compact e-cash schemes are constructed from either verifiable random functions or bounded accumulators. We use both building blocks to construct the new scheme which is secure under the $q$-SDH, the $y$-DDHI and the SXDH assumptions in the random oracle

model.