# Hard-drive space as a tangible, scarce Sybil resistance resource: the PoST protocol

Proof of Space-Time (PoST) is a new cryptographic primitive, designed to replace Proof of Work (PoW) as a proof-of-resource-consumption scheme, and so as a Sybil-resistance mechanism for permissionless cryptocurrencies. It was introduced in 2016 by Tal Moran and Ilan Orlov in a paper titled “Simple Proofs of Space-Time and Rational Proofs of Storage.”

A PoST allows a prover to convince a verifier that they expended a certain amount of a “space-time” resource: a specific amount of space allocated over a specific time period, during which the space cannot be used for anything else. …

# Proof-of-Work: Female Seduction, Good Name for Kings, Combatting Junk Mail and Crypto-Anarchism

Let’s say, hypothetically, that you would like to torture someone.

One possible way, and perhaps one of the cruelest, would be to simply make him work, but to give his labor a character of complete uselessness. Just make him do something that has no utility, no purpose, and no meaning. And to make it even worse, make it be something really stupid that he cannot even strive to do skillfully.

Assuming you do not have the resources nor the will to continuously watch him, his work must produce something that will serve as a measurement of the amount of effort…

# An Appendix: Partial Hash Collisions

This is an appendix to the article — Proof-of-Work: Female Seduction, Good Name for Kings, Combatting Junk Mail, and Crypto-Anarchism

## Cryptography 101

A hash function is a function that takes any input and produces a fixed-size output, with an efficient computing procedure.

A cryptographic hash function is a hash function that has the following properties, which make it suitable for use in cryptography:

• Collision Free: Nobody can find two inputs which produce the same output.
• Hiding: Given the output, nobody can find the input.
• Puzzle Friendly: If someone wants to find an input that produces a specific output, there isn’t any better…

# Forks in the Blockchain: Discrepancies Between Competing Chains

“Satoshi Nakomoto’s main invention is the decentralized mechanism for emergent consensus. Emergent, because consensus is not achieved explicitly — there is no election or fixed moment when consensus occurs. Instead, consensus is an emergent artifact of the asynchronous interaction of thousands of independent nodes, all following simple rules.”

~ Andreas Antonopoulos, Mastering Bitcoin

When you cannot, or simply choose not to trust any form of central authority, you are positioned in a new paradigm of trust where one cannot simply ask an oracle — a centralized service — about the current state of the system. …

## Moshe Shababo

“There is no fate that cannot be surmounted by scorn”

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