Double-Spending Fast Payments in Bitcoin due to Client versions 0.8.1

Abstract

In this article, we discuss a possible exploit in Bitcoin that arises from the simultaneous adoption of client versions 0.8.1 and 0.8.2 (or 0.8.3) in the network. In version 0.8.2, Bitcoin clients no longer accept transactions with non-strict signature encoding. As we show, this incompatibility with prior client versions can potentially lead to a double-spending attack in a fast payment setting in Bitcoin. The attack can only work when merchants operate on any client version prior to 0.8.2. Our aim is therefore to raise the awareness of merchants to adopt version 0.8.2 (or 0.8.3) if they are willing to accept fast payments [1].