using e-coins to ensure fair sharing of donor funds amongst hiv healthcare facilities

Donor funds are available for treatment of many diseases such as HIV. However, privacy constraints make it hard for donor organisations to verify that they have not sponsored the same patient twice --- or sponsored a patient whose treatment was also sponsored by another donor. This paper presents a protocol based on digital cash that enables donor organisations to obtain a proof (in the form of an e-coin) from healthcare providers for patients such a provider claims to have treated. These coins are distributed to patients at the beginning of a funding cycle. The major challenge is to issue a unique coin to a patient --- even if the coin is reissued. This is achieved without giving anyone access to a national database of identities; all databases contain effectively concealed information. Reissued coins will be identical to previous coins with a probability that can be decided beforehand.