Digital cash protocols are starting to look like they could become very popular and useful. But under current proposals, there's one thing you don't get when you spend digital cash: a digital receipt. (Later, if the vendor reneges on the transaction, you'd have the digital receipt to prove that you paid & the vendor is cheating you.) This seems like it would be a really useful feature. Does anyone know if there are any *practical* protocols to do this? ObCypherpunks relevance: digital receipts seem (IMHO) important to the emergence of fair and robust reputation markets. Discuss. ObCrypto relevance: I've looked through _Applied Cryptography_, but the protocols listed there aren't practical -- they require something like 100 rounds of interaction! Can this be improved?