Bit Gold

Bit Gold is a proposal by computer scientist and legal scholar Nick Szabo for a decentralized digital currency built on chained proof-of-work. Szabo conceived the idea around 1998 and described it publicly in 2005. It is frequently cited as one of the closest conceptual precursors to Bitcoin, to the point that Szabo has been a recurring (and consistently denied) candidate in speculation about Satoshi Nakamoto's identity.

How it would have worked

In Bit Gold, a participant solves a computational puzzle of known difficulty. The solution is timestamped and cryptographically linked to the previous solution, forming a chain of proof-of-work attributed to the solver's public key. Because each unit is scarce, costly to produce, and securely transferable, it could function like a digital analogue to gold, valuable precisely because it is provably hard to create. This chaining of proof-of-work strings closely foreshadows Bitcoin's blockchain.

The missing piece

Bit Gold was never implemented. Its unresolved gap was consensus: it lacked a robust mechanism for the network to agree, without a trusted party, on which puzzles were valid and how to prevent double-spending of the resulting units. It also had no built-in way to keep the cost of producing new units stable as computing power grew. Bitcoin's longest-chain rule and difficulty adjustment supplied exactly these missing components.

For the parallel proposal from the same era, see b-money, and for the design that finally solved consensus, the Bitcoin whitepaper.