- Sufficiently high market cap
- Sufficiently large block waiting time until a merchant transfers a physical good

Protections against double-spending attacks in Proof-of-Stake

- An attacker purchases a physical good with a number of native coins
- A merchant transfers possession of the physical good after waiting for a certain number of blocks to be linked to the transaction
- Once the attacker receives the physical good, they create a new branch without the transaction
- For the attack to succeed, the new branch must become as long as the initial branch

Implementation of a double-spending attack in Proof-of-Stake

A double-spending attack is when an attacker uses native coins to purchase a physical good, but then attempts to reverse the transaction to regain possession of their coins. 

University of Minnesota - Twin Cities

- Nothing-at-Stake problem
- Validator fraud
- Wealth concentration
- Double spending
- Staking pools

Concerns regarding Proof-of-Stake

Saleh, Fahad. (2021). Blockchain Without Waste: Proof-of-Stake. Wake Forest University. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3183935


Blockchain Without Waste: Proof-of-Stake

Like Proof-of-Work (PoW), Proof-of-Stake offers validators a monetary reward for updating the blockchain. However, it does not impose a monetary cost, such as that incurred from solving PoW problems. Hence, the Nothing-at-Stake problem, detractors assert, implies that validators will always update the ledger, even if it unnecessarily perpetuates disagreement. 

Nothing-at-Stake problem

Validator fraud happens when a validator is able to steal coins from other users.

Validator fraud

Wealth concentration is the concern that Proof-of-Stake will lead to the rich getting richer, causing a concentration of wealth.

Wealth concentration

Double spending

Staking pools are organizations of individual stakeholders join together to share rewards from validation.

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