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