When The "Crypto" in Cryptocurrencies Breaks: Bitcoin Security Under Broken Primitives

Abstract

Digital currencies such as Bitcoin rely on cryptographic primitives to operate. However, past experience shows that cryptographic primitives do not last forever: increased computational power and advanced cryptanalysis cause primitives to break, and motivate the development of new ones. It is therefore crucial for maintaining trust in a cryptocurrency to anticipate such breakage. We present the first systematic analysis of the effect of broken primitives on Bitcoin. We analyse the ways in which Bitcoin’s core cryptographic building blocks can break, and the subsequent effect on the main Bitcoin security guarantees. Our analysis reveals a wide range of possible effects depending on the primitive and type of breakage, ranging from minor privacy violations to a complete breakdown of the currency. Our results lead to several suggestions for the Bitcoin migration plans, and insights for other cryptocurrencies in case of broken or weakened cryptographic primitives.