Nick Szabo, Bit Gold https://nakamotoinstitute.org/bit-gold/
Satoshi Nakamoto, Whitepaper https://bitcoin.org/en/bitcoin-paper
Vitalik Buterin, Hard Problems in Cryptocurrency (2014) https://github.com/ethereum/wiki/wiki/Problems/89fd07ffff8b042134e4ca67a0ce143d574016bd
Vitalik Buterin, Hard Problems in Cryptocurrency (2019) https://vitalik.ca/general/2019/11/22/progress.html