PayTree: "Amortized Signature" for Flexible Micro-Payments
The authors present the idea of PayTree, a method to amortize the work of a single signature production and verification among numerous micropayments in the model where payments are made from a payer to a set of merchants (under various trust assumptions regarding these merchants). The PayTree scheme is simple yet flexible. Its main feature is that it can support arbitrary (dynamically determined) number of payees while using a single signature (unlike PayWord). It is therefore suitable for supporting users who "Shop around". The scheme is easily extendible dynamically (without the use of further signatures) and has a reasonable computational penalty. It can be viewed as a "Divisible coin" mechanism as well.