Abstract
The security of any proof-of-work blockchain protocol is based upon the assumption that the probability of a miner finding the next valid block is proportional to that miner’s hashing power and constant throughout the process of mining that block (i.e., that the mining process is a “memoryless” process). While the literature assumes that the mining process is indeed memoryless, in this paper we use deductive reasoning to show how, given the finiteness of hashing functions’ domains, this is not the case. This implies that the Bitcoin protocol induces a centralization of miners’ hashing power, which in turn threatens the long-term viability of Bitcoin and of other cryptocurrencies based on similar protocols. The novelty of this paper stems from our documenting of a previously unrecognized flaw in the incentive system sustaining Bitcoin’s security.
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Notes
From this point on we will use the terms “selection rule” and “winning probability” in an interchangeable manner.
In fact, miners pass the block header through the SHA-256 function and hash the resulting 256-bit string again using the same SHA-256 function. It is the second hashing that needs to result in a number below the target. Since the SHA-256 function is deterministic, this does not alter our calculations.
Note that this 5% is an approximate figure indicating the area of the sample size around which this difference starts to matter (rather than a dichotomous threshold that should serve as a hard line).
The global hash rate of Bitcoin can be consulted at any time at sites such as https://www.blockchain.com/explorer/charts/hash-rate.
Note that the average annual growth rate of the hashpower of Bitcoin between September 2019 and September 2023 lies at 266%. See https://ycharts.com/indicators/bitcoin_network_hash_rate for the reference.
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Parra-Moyano, J., Reich, G. & Schmedders, K. A Note on the Non-proportionality of Winning Probabilities in Bitcoin. Comput Econ (2023). https://doi.org/10.1007/s10614-023-10503-2
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DOI: https://doi.org/10.1007/s10614-023-10503-2