“Hard Problems in Cryptocurrency: 5 Years Later”, Vitalik Buterin2019-11-22 (, ; similar)⁠:

[Vitalik Buterin of Ethereum reviews cryptocurrency technological developments since 2014, in cryptography, consensus theory, & economics:]

  1. Cryptographic:

    • Blockchain scalability: Great theoretical progress, pending more real-world evaluation.
    • Distributed secure timestamping: Some progress.
    • Arbitrary Proof of Computation: Great theoretical and practical progress. [SNARKs/STARK/SHARK etc]
    • Code Obfuscation [DRM]: Slow progress.
    • Hash-Based Cryptography [which is quantum-secure]: Some progress.

  2. Consensus theory:

    • ASIC-Resistant Proof of Work: Solved as far as we can.
    • Useful Proof of Work: Probably not feasible, with one exception.
    • Proof of Stake: Great theoretical progress, pending more real-world evaluation.
    • Proof of Storage: A lot of theoretical progress, though still a lot to go, as well as more real-world evaluation.

  3. Economics:

    • Stable-value cryptoassets: Some progress.

    • Decentralized Public Goods Incentivization: Some progress.

    • Reputation systems: Slow progress

    • Proof of excellence: No progress, problem is largely forgotten.

    • Anti-Sybil systems: Some progress.

      • Decentralized contribution metrics: Some progress, some change in focus.

    • Decentralized success metrics: Some progress.

…In general, base-layer problems are slowly but surely decreasing, but application-layer problems are only just getting started.